Electronics: June 2020

Capacitors store energy as electric

Inductors as magnetic

1 june 2020

Low pass filters

Input/Output impedance

2 jun

High pass filters - only high frequencies

Band pass filters - only allow a band of frequencies to pass

Notch filters - allow all frequencies except a band in the middle

3 jun

Attenuators

1. using simple resistors based voltage divider to reduce voltage - independent of frequency

2. capacitors added to deal with stray capacitance. r1c1=r2c2 so divider remains frequency independent

4 jun

Transient circuits

1. In DC, the time when switch is opened/closed, voltage/current changes

2. In RC, capacitor starts charging, full (V/R) current initially, decreases to 0 when cap fully charged

3. In RL, inductor initially blocks current, 0 current initially, increases to V/R when inductor turns to wire

4. Time dependent formulae for current, voltages across R/L/C

5. In case resistance is increased by switch (no impact on source voltage), inductor doesn't let current to drop so supplies increased voltage (VL), total current = supplied by inductor (VL decreasing by time)

+ supplied by source

6 jun

Transient circuits contd..

1. There are three ways to calculate inductor's response (induced voltage) to change in current/resistance/voltage

a. using the concept that inductor will increase it's voltage to ensure current remains as before (#5 above)

b. induced voltage will be proportional to change in current

c. using formula, induced voltage = Ae^(-rt/l), total current = forced + induced, calculate A using values at t=0

7 jun

1. Series RLC circuit (another example of transient - damped harmonic oscillator)

2. if linear first/second order homogeneous differential equation, it will reduce to i=i0*e^at

3. Overdamped: R is large (eg. 200 ohm), current reaches higher peak (transfer from capacitor to inductor), reduces to 0 quickly (as a function of time)

4. Critically damped: R is medium (R^2=4L/C, eg. 100 ohm), current reaches lower peak (~half of case 1) and dampens slowly (~2 times case 1)

5. Underdamped: R is small (ex. 10 ohm), current is sinusoidal, reaches even higher peak (~double) than case 1, dampens slowly (~4 times case 1)

9 jun

Nonsinusoidal periodic sources

1. Fourier series, can be expressed as a summation of multiple sinusoidal waves

2. All functions: V(t+/-T) = V(t), V(t+/-T/2) = -V(t)

3. Even function: V(t) = V(-t), only cosines remain

4. Odd function: V(t) = -V(-t), only sines remain, no DC component

5. Square wave is an odd function (if looked from t=0), even function if looked from t=T/4 (for e.g)

6. There are formulae for common waveforms: square, triangle, sawtooth etc.

6. Very good video on fourier transformation - combining/de-combining waves

11 jun

SPICE

1. https://www.circuitlab.com/

2. Can quickly change component values to see voltage/current/waveform/other behaviours in circuit

3. Internal calculations are based on conductance, using matrix multiplications/inverse etc.

4. Limitations: does not include noise etc. and hence actual breadboarding is unavoidable

12 jun

Wires, cables, connectors

1. Higher gauge, thinner wire, more resistance per foot

13 jun

High frequency effects on wires/cables

1. Skin effect

2. Can be seen as made up of lots of inductors and capacitors

3. Impedance Z = sqrt (L / C), vary with di-electric, area etc.

4. Impedance matching:

a) if unequal, loss of power (wavelength change, amplitude change), reflection

b) how to match impedance (using R/L/C voltage dividers)

15 jun

Primary and secondary (re-chargeable) batteries
Memory effect
Red/Green led to indicate battery level using resistor voltage divider and transistor as a switch

16 jun

Switches

Poles - how many circuits the switch can control
Throws - how many outputs each pole can be connected to

17 jun

Relays - mechanical, reed, solid state

AC and DC coils (coils powered by DC/AC source)

Using transistor and relay combination (like we did in raspberry pi dashcam) for low/high current setting

18 jun

Resistors - fixed, var, photo, pots, fusible

power rating, voltage rating; choose whose power rating >=2*expected power

current divider, i1 = [r2/(r1+r2)]*i

voltage divider, v1 = [r2/(r1+r2)]*v

tolerance (+/-5% ok for most), reliability (dR=per 1000 hrs), temperature coefficient (dR=ppm/C/ohm)

power rating v temperature

resistance v temperature (coefficient)

frequency v resistance

Resistor types

Potentiometers - a current divider when 2 pins are used, is a voltage divider in itself when 3 pins are used

The key features of current limiting and voltage setting are implemented in various ways in electronics. Resistors are used to set operating current and signal levels in circuits, provide voltage reduction, set precise gain values in precision circuits, act as shunts in ammeters and voltage meters, behave like damping agents in oscillators and timer circuits, act as bus and line terminators in digital circuits, provide feedback networks for amplifiers, and act as pullup and pulldown elements in digital circuits. They are also used in attenuators and bridge circuits. Special kinds of resistors are even used as fuses.

21 jun

Capacitors

AC coupling, decoupling, passive/active filters

Non-ideal capacitor parameters:

leakage (parallel resistance), equivalent series resistance (ESR), equivalent series inductance (ESL), and dielectric absorption (memory) = (self recharge voltage/voltage before discharge)

DCWV, Dissipation factor (1/Q), Q = XC/Resr,

Insulation Resistance(?looks similar to RL, resistance to DC)

Temperature coefficient, IR decreases with temperature

Larger capacitance, smaller resonant frequency

Type of capacitors electrolytic, tantalum, ceramic, plastic film, variable

Capacitor functions - pg 325 photo

Capacitor types (pg 337): Trimmer, air core, vacuum, aluminium/tantalum electrolyte, polyester/polypropylene film, silver mica, ceramic - single/multi layer

Capacitor applications

1. AC Coupling and DC blocking

2. Bypassing

Power supply bypassing

1. noise

2. high current draw from attached device

Shorter leads better

Selecting decoupling caps - rules

1. every IC 0.1 uF per VCC-GND

2. power line start and end: 0.001 uF, 0.01 uF, 1uF (tantalum) in parallel at start and end

3. Placement as close as possible - tick tracks, leads < 1.5mm

4. Lower capacitance for higher frequencies blocking

Consider interface frequency, CPU frequency?

Low-Med-High frequency spectrum

AF = 20 Hz - 20 KHz (audio)

LF = 30 KHz - 300 KHz (RF)

MF = 300 KHz - 3 MHz

HF = 3 MHz - 30 MHz

VHF = 30 MHz - 300 MHz

UHF = 300 MHz - 3000 MHz (3 GHz)

Timing capacitor

Relaxation oscillator: square wave generator

1. Inverter IC - what is it's high/low

2. RC (wave low duration = discharge time, high duration = charge time)

Sample and hold

26 jun

Capacitor applications contd...

1. RC ripple filter - full/half wave rectifier, formulae for ripple factor etc.

2. Speaker crossover network - LR for low freq (woofer), RC for high freq (tweeter)

3. Arc suppression: V<300v, dV/dT<1V/uS, I < minimum arcing current for switch

> Snubber R and C calculation to maintain above levels

4. Active filters: low/high pass filters combined with Op-amps

27 jun

Super capacitor applications

1. Solar energy storage without battery

2. Photosensor based

3. Power backup with current limiting circuit (working not clear) pg 353

Not in this section but other not clear item is - thevenin / norton

For many audio applications, polypropylene and polyester film and even an electrolytic capacitor may be good choices, but for a high-frequency, high-stability decoupling application, up into the megahertz range, an NPO multilayer ceramic capacitor may be required.

28 jun

Inductors

1. Band pass (LC series resonant) and notch filters (LC parallel resonant)

> audio carrier signals, tuned circuits for radio reception

2. Boost and buck converters (

3. Solenoid - open/close doors, valves, switch contacts (relays)

4. Transformers

Non ideal real life resistor, capacitor and inductor

RC / RL charging discharging formulae (page 226)

30 jun

Inductor applications

1. Application v key criteria (not clear) page 363, table 3.8

2. Inductor types, labels

2 july

Inductor applications

1. Filters: low/high/band pass. Differential mode high pass filter (not clear) pg 369

2. Switching regulators (buck/boost/buck-boost)

3. Oscillators - Op amp, colpits, hartley (not clear)

4. Radio circuits - short wave receiver, RF oscillator / transmitter (not clear)

3 july

EMI/EMC design tips

- most things in this section are not clear (page 373)

- from engg. note at this link. Better read the whole note instead of subset in book.

6 july

Transformers

Vs/Vp=Ns/Np, Is/Ip=Np/Ns, Zs/Zp=sqr(Ns/Np), Ps/Pp=n (65-99%)
Phase difference

Vp v Vs = 0 (winding/current in same direction) / 180 (opposite)
Ip v Is = 0 / 180
Vp v Ip = 90 (without load) / 0 (resistive load) / X (reactive load)
Vs v Is = same as Vp v Ip
Phase difference does not matter in many circuits ex. AC step-down
Phase difference matters in ex. joule thief (video)

Impedance matching: Creating required primary impedance by selecting Np/Ns to match the load in secondary

7 july

Transformers Contd...

Gear analogy: Voltage = torque, current = speed
Bigger gear (more windings) —> more torque (voltage), less speed (current)
Variac
Single winding transformer: use isolation where needed

10 july

Transformers contd…

1. Boosting and bucking - 3rd alternative using wires in series but autotransformers (single wire) are better

2. Isolation transformer - output from secondary (source and return) are not connected to ground hence no shock if you touch

11 july

Transformers contd…

Types: power, audio, air core rf, ferrite/powdered iron toroidal, pulse/small signal

Transformer application categories:

to transform voltages and currents from one level to another
to physically isolate the primary circuit from the secondary
to transform circuit impedances from one level to another.

Transformer Applications:

Current measure
Centre-Tap pole (high power to low for homes)
Landscape lighting (multiple voltages) - overall power drawn < capacity
Step-down DC
Transformers-rectifier combinations

Dual complimentary - not clear
Full/half wave
Full wave center tap

Audio impedance matching: Load input impedance should be >= source output impedance

12 july

Fuses and circuit breakers

fast action and time lag
each device should have it's own individually rated fuse (not rely on main circuit breaker rated at higher current)
fuse current rating should be ~50% larger than expected nominal current rating

13 july

Semiconductors

1. Silicon, doping (phosphorus n-type, boron p-type)

2. water analogy (holes don't travel but it appears so - can be related to positive charge of protons)

3. Applications: Diodes, transistors, LEDs, solar cells etc.

15 july

Diodes

P-N junction, Rectifier are diodes that can handle high current

Used in (applications): voltage-multiplier, voltage-shifting, voltage-limiting and voltage-regulator circuits

Types

Silicon - 0.6V, better heat dissipating, high current (rectifiers)
Germanium - 0.2V, not above 85*C, can detect lowest voltage, high frequency signals, replaceable by schottky
Schottky - 0.4V, very low junction capacitance and faster switching (~10 ns), low heat, metal-semiconductor junction i/f, lower junction threshold voltage (0.15v), detects low voltage high frequency signals

16 july

Characteristics

Peak inverse voltage, PIV;
forward current-handling capacity, IO(max) ;
response speed tR (time for diode to switch on and off);
reverse-leakage current, IR(max) ;
maximum forward-voltage drop, VF(max);
peak surge current (Ifsm)

Types: signal, fast switch, rectifier, schottky

Diode/rectifier applications

Voltage dropper - better than resistor as more stable output voltage even with varying current
Voltage regulator
Reverse polarity protection - series, parallel (better)

Transient suppression with fly-back diodes applications

Transient protection. Inductor's magnetic field collapses inducing negative voltage & then it gets fed back the same into the other end (via diode) hence the oscillating wave.
Transistor relay driver with protection diodes - 2nd diode across transistor (to protect it) not clear (pg 413).
Motor inductive kickback protection

17 july

Diode clamps applications - clip signal levels, or they can shift an ac waveform up or down

Adjustable waveform clipper
Adjustable attenuator
Diode voltage clamp (DC resotration) - not clear
Diode switch
Half-wave rectifier
Full-wave center-tap rectifier
Full-wave bridge rectifier

18-19 july

Voltage multiplier circuits (applications)

Half-wave voltage doubler
Full-wave voltage doubler
Voltage tripler - not clear (why polarised capacitor?)
Voltage quadrupler

Low current load & RC >> time-period of input AC.

After capacitor is charged, it retains it even if connected to ground (attraction force between two opposite charged plates)

Read charged capacitor as battery to understand total voltage at a node

21 july

Diode logic gates (applications)

AND, OR gates - pull-down (or pull-up) resistors are needed so inputs (A/B/C that can be microcontroller's pins) do not be dangling / floating at any point
Battery backup - ICs are better since diode, being in series, eats up voltage
AM detector - diode just eats lower half of wave, LC tuning circuit, RC low pass filter
Schottky diode termination - diode with ground at anode makes sure no negative voltage passes through (clamping)
ROM

Zener diodes

Reverse bias is the default mode
Keeps voltage across itself constant - by reducing it's resistance, more current passes; acts like a variable resistor
Voltage regulator

variable supply voltage
variable load resistance

Temperature dependent so not for critical applications, used to supply reference voltage

22 july

Zener diode applications

Split supply from single transformer winding - 0V in between
Waveform modifier and limiter - clip both ends using 2 opposite zeners
Voltage shifter - will pass (V-Vz) after threshold, graph slightly incorrect
Voltage regulator booster - move ground to Vref, Output = Vout+Vref
Overvoltage protection - zener will be reverse biased when voltage increases (beyond desired level), will conduct till fuse is blown
Increasing wattage rating of zener - can handle higher current/wattage using a transistor. Zener controls base supply and overall voltage across transistor (Vce). Why Vbc=Vce? Why not Vbe+Vcb=Vce? not clear
Simple LED voltmeter - increasing number of LEDs glow as V increases

Varactor Diodes (Variable Capacitance Diodes)

As voltage increases, width of junction increases, capacitance decreases
Used in high frequency RF circuits, change capacitance --> change oscillator frequency
Reverse bias voltage should be noise free - can use filter capacitors

Varactor diode applications

FM modulator - LC tuning circuit that drives oscillator to generate wave of carrier frequency. Varactor changes C based on input signal (amplitude/voltage) and hence frequency of oscillator (superimposing signal on carrier). Colpitts LC oscillator not clear.
Oscillator with Pot-Controlled Varactor Tuning - Pot changes C (via dual varactors) in the LC tuning circuit and hence the frequency of oscillator. N-channel JFET and the circuit not clear.

23 july

PIN diodes (P-Intrinsic-N)

Acts like a variable resistor whose value is controlled by an applied dc forward-bias current
Applications

transmit/receive switches in transceivers operating from 100 MHz and up
photodetectors in fiber-optic
RF switching (spst and spdt)

Microwave Diodes (IMPATT, Gunn, Tunnel, etc.)

Problems

Diode when reverse biased does conduct (leakage current), not 'open circuit', so there will be voltage drop that can be calculated using kirchoff law close loops. R(load) minimum would be V-2*(diode fwd drop). Double it.
Clamping circuit. Wave is pushed by Vpeak - diode drop (0.6v). With load, voltage reduces, high-pass (RC) filter and it's cut-off frequency comes into picture. Actual voltage/current can be calculated through simulation/actual breadboarding
Varying supply and load current - Rs(max) can be calculated considering min input V, max I drawn by load. In this case, Rs should be low enough to ensure load works in these conditions. In case of max V, min I drawn by load, zener will absorb more current. Power rating for:

Rs: sqr(Vinmax-Vz)/Rs
Diode: Vz * (Vinmax-Vz)/Rs. Don't consider current eaten by load.

LED and Laser diodes

Zener, photo diode and varicap/varactor work in reverse-bias mode

24 july

Transistors Introduction

25 july

Transistors contd...

Cut-off, saturation, active regions (Q point - desired V/I within active)
Rule 1 (npn): Vc > Vb + few 10th of volts. Reverse for pnp
Rule 2 (npn): Vb > Ve + 0.6. Reverse for pnp
There are limits for max V/I across the transistor
Ic=Hfe*Ib given

temperature, Vce remains fixed
rule 1 & 2 satisfied i.e., in active region

Ie = Ic + Ib (emitter always has max current) for both npn and pnp
Ic = Ie approx if Hfe is large (mostly the case)
Trans-resistance = 0.026/Ie
Applications (Configurations): electrically controlled switching circuits, current-regulator circuits, voltage-regulator circuits, amplifier circuits, oscillator circuits, and memory circuits
Switch NPN

Load should not drop Vc so much that rule 1 breaks
R1 should be such that Vcc >= 0.6
R2 should be large so very less I flows to ground (in OFF situation)

11. Switch PNP

R2 should be high so Ib to ground is low in ON situation
R2 & load resistance are related as both are passing current when ON and their currents are related Ic = Hfe * Ib
R1 should be (small and) such that Ve-Vb<=0.6 to switch OFF

12. Current source

Ic = Iload = (Vb-0.6) / Re.
Base voltage & emitter resistor are driving current at load (collector)

26 july Transistor applications (configurations) contd...

13. Current biasing methods:

same voltage source for C and B
split voltage using resistor divider or zener

14. Emitter follower

no voltage gain, high current gain, negative spike is clipped
Vout=Vin, Iout=Hfe*Iin, Rout = Rin / Hfe
Approximations done ignoring 0.6v, (Re||Rload = Re) etc.
Input impedance can be calculated hiding start of circuit - consider everything towards the right including load
Output impedance can be calculated hiding load - consider everything towards the left

15. Emitter follower (common-collector) amplifier

Current gain, no voltage gain
Capacitors at both ends to pass (and filter) AC, high-pass filters, no clipping
Resistor voltage divider adds DC to ensure full signal passes (Vdc-Vpeak>0.6) at all times
Choose component values as per desired output
Use input/output impedance calculation (from #14) considering DC and AC aspects
(Input impedance of load) should be > 10 * (output impedance of source)

27 july Transistor applications (configurations) contd...

16. Common-emitter configuration

Vout from collector, voltage gain, current gain?
Vout = Vc = 1/2 Vcc to allow for max swing without clipping (not clear). This is same as common-collector when Vout was from emitter
Gain = -Rc/Re, negative since Vb increase -> Ic increase -> Vc decrease
'deltas' (change) in V/I in formulae due to AC
Add Re to stabilise gain, add C to increase gain

17. Common-emitter amplifier

Similar to #15 except Vout from C hence a resistor there
Only 1V at Ve (for temperature stability) since you don't take Vout from E

28 july Transistor applications (configurations) contd...

18. Voltage regulator

with zener - output of zener is input (base) of transistor
zener and two transistors - output (emitter) of 1 transistor is input (base) of other
Darlington pair: 2 transistors as above. Hfe = Hfe1 * Hfe2. Large current, high input impedance but voltage drop double (0.6*2) and slower response

Note (for most transistor applications):

For voltage amplification, output from Collector only

For current amplification, output from Emitter (or Collector)

Transistor types

Important points: Maximum current (Ic/Ib/Ie) and breakdown voltage ratings (Vbe/Vcb/Vce) must be respected. Diodes to avoid.

Digitmal multimeter to detect transistor type (npn/pnp), pinout designations (ebc/cbe etc) and hfe

29 july

Transistor applications

1. Relay driver: low->high current, flyback diode

2. Differential amplifier

two inputs, amplifies the difference, common-emitter
used to remove noise/EMI that get on both wires
gain = Vout / (V1-V2)= Rc/Rtr
CMRR (video)

Common mode rejection ratio
should be infinite (more the better)
varies with frequency of input (decreases as noise frequency rises)
Low frequency noise can be filtered out using low pass filter
When V1=V2, Vout should be 0 but it's not (Vocm)
Vocm = Acm * Vicm (common mode)
In differential mode, Vout = Ad * Vid + Vocm
CMRR = Ad / Acm = 20 log (Ad/Acm)
Datasheet has value for open-loop, same is approximately valid for closed loop (i.e., more practical circuits)
Op-amp is very similar to differential amplifier

30 july

3. Complementary-symmetry amplifier

npn and pnp: switch on complimentary at +0.6 and -0.6 respectively
crossover distortion near 0v
used in dc amplifier - not clear

4. Current mirror

2 pnp (or npn)
control current in one (using resistors + feeding one's collector into base of both), and that will reflect into other (with load)

5. Multiple current sources

extend above with 3 load transistors
add 1 extra transistor on 'control' side to avoid a 'saturated' (eg. load removed) transistor 'steal' large I reducing I for others - not clear

6. Bistable multivibrators (flip flops)

Transistor states (operation modes)

Saturation -- The transistor acts like a short circuit. Current freely flows from collector to emitter.

Cut-off -- The transistor acts like an open circuit. No current flows from collector to emitter.

Active -- The current from collector to emitter is proportional to the current flowing into the base.

Reverse-Active -- Like active mode, the current is proportional to the base current, but it flows in reverse. Current flows from emitter to collector (not, exactly, the purpose transistors were designed for).

Above videos are using transistors. Multivibrators can be made using Op-amp and 555 timer IC too.

Notes:

One transistor starts conducting before the other
If a capacitor is charged with +V at plate A and you apply 0V to A then B becomes -V

7. Transistor logic gates - OR, AND

31 july

JFETs (junction field-effect transistors)

normally on (when Vbs = 0), apply -ive at base, starts resisting
high input impedance ~10^10 ohms!
Applications: bi-directional analog switching circuits, input stages for amplifiers, simple two-terminal current sources, amplifiers, oscillators, electronic gain-control logic switches, audio mixing circuits etc.

JFET states

Cut-off (Vgs-off ~ -0.5 to -10v)
Ohmic region (Vds controlled resistor)
Active (Vgs controlled)
Saturation (Idss constant ~ 1mA to 1A)
Breakdown (Bvds ~ 6-50 v)

Transconductance, On resistance, Input impedance: relation not clear

1 Aug

JFET Basic operations (applications)

1. Light dimmer: 3 JFETs each with bulb, different voltages at base

2. Basic current source and amplifier: shorting source and base (self-biasing), Vgs=0, max current (Idds) not stable, add resistor b/w source and ground to improve stability. not as stable as good bi-polar/op-amp current source

3. Source follower (common drain) - not clear

AC applied to JFET
Vgs not stable, Vout not stable (because of gm etc.)
Add bi-polar transistor to improve - not clear how bi-polar fixes voltage at base
Add JFET to improve - not clear
dId = dVgs * gm (gm is equivalent to beta from bipolar)
rd = dVds/dId @ Vgs (output impedance)
Input impedance is considered infinity

2 Aug

JFET notes from youtube - all about electronics videos

Vp is pinch-off voltage, consider 'negative' e.g. -4v
Graph is most important to understand regions
Any circuit, understand which region it is operating in (Or assume saturation & then validate it)
Ohmic: fix resistor if Vds vary (<Vgs-Vp), Vgs fix (between 0 and Vp)
Saturation: variable resistor if Vgs vary (b/w 0 and Vp) & Vds fix (>= Vgs-Vp)

application: linear amplification of AC signal (not clear)
Id = Idss * (1-Vgs/Vp)^2

Cut-off: Vgs <= Vp, Id = 0, application: switch (b/w cut-off and saturation)
Biasing: fixed (using another battery at G), self (shorting S and G/via resistor), voltage divider
Self-bias: If Id increases due to temperature --> drop across Rs increases --> Vgs increases --> Id decreases, stabilises the operating point

4 Aug

JFET amplifiers (configurations)

Source follower: current gain, output from S, not clear
Common source: voltage gain, output from D, not clear, gain significantly smaller than bipolar
Voltage controlled resistor: operate in ohmic region, works as variable resistor controlled via input at G. Used in gain-control, attenuators, variable filters and oscillator amplitude-control circuits

5 Aug

Practical considerations

JFET application categories

Small-signal and switching JFETs are used to couple a high impedance source with amplifier or oscilloscope
Voltage controlled switches
High frequency JFETs used to amplify high frequency signals (RF) or high frequency switch
Dual JFETs used to improve source follower circuit performance

Same JFET type (e.g. 2N5457) can have 2 different Vp (cut-off voltage), different Id at same Vgs/Vds! not clear

JFET Applications

Relay driver
Audio mixer / amplifier
Electrical field meter

7 Aug

MOSFETs

Even greater input impedances (~10^14)
Depletion - similar to JFET
Enhancement - similar to bipolar
Gain = gm * Rd
Fourth lead (body terminal): held at a non-conducting voltage
Damaging is easy, even with static charge
Types: switching, high power, high/low driver ICs

MOSFET Applications

Light dimmer
Current source - highly reliable (<1% error)
Amplifiers: source-follower, common-source
Audio amplifier
Relay driver (digital to analog conversion)
Direction control of a DC motor

10 Aug

Insulated gate bipolar transistors (IGBTs)

Voltage controlled like MOSFET, high current capabilities like bipolar
For very high power applications like electric vehicles

Unijunction transistors (UJTs)

Only switch (not amplifier)
Voltage applied at emitter (E), large current starts from E to B1
Equivalent to a diode at E and resistor divider b/w B1 and B2
Voltage vs current graph not clear
Types:

Basic switching: used in oscillatory, timing and level-detecting circuits
Programmable (PUTs): can be programmed using external voltage divider, used in timer, high-gain phase control, oscillator circuits

UJT applications

Relaxation oscillator (common principle behind most of it's applications)

sawtooth wave converted to small pulses
OFF while capacitor (C) charges, ON when C charged>Vtrigger, stays on till C discharges below Vtrigger
C and resistors control frequency and amplitude of output

Timer / relay driver: switches the relay ON/OFF repeatedly using C
Ramp generator with amplifier: generates sawtooth using C and bipolar
PUT relaxation oscillator: generates sawtooth and spikes, take output from both sides of C

Thyristors

Only switches (not amplifiers): a switch of accuracy higher than bipolar (which has a middle state b/w ON and OFF)
Applications: speed control, power switching, relay replacement, low cost timer, oscillator, level-detector, phase control, inverter, chopper, logic, light-dimming and motor speed control circuits
Types:

SCR: ON when I enters G, OFF when anode-to-cathode current stopped
SCS: extra lead to switch ON/OFF by applying voltage
Triac: two way current (AC), ON only when G is receiving current
Four-layer diode: 2 leads, ON only when V > breakdown point
Diac: similar to 4 layer but conducts in both directions (AC)

Silicon controlled rectifier (SCR)

3 leads, normally off, when a small I enters G, it turns on, does not switch OFF even if current is removed from G, anode-to-cathode current flow must be stopped e.g., by reversing voltage polarity
Applications: switching, phase control, inverter, clipped, relay control circuits
Types: Low/Medium/High voltage/current. Can be several thousands V/A
Equivalent circuit: npn and pnp transistors sandwiched together

SCR applications

Basic latching switch: remains on after a push button spike at G
Rectifier: Clips AC input controlled by a variable resistor. Does not waste any power in resistive heating
DC motor speed control: by switching it on and off using C and variable R

Silicon controlled switches (SCS)

Increased control, triggering sensitivity and firing predictability
Turn-off time 1-10 ms (for SCR it is 5 to 30)
Lower power/I/V ratings (than SCR)
Can be ON/OFF by +/- voltages at both gates individually
Equivalent circuit: back-to-back bipolar transistor network
Applications: any circuit that needs ON/OFF using 2 distinct control pulses, power switching, logic, lamp drivers, voltage sensor and pulse generators

Triacs

If gate voltage is removed, triac switches off when AC voltage crosses 0 V
Applications: ac motor control, light dimming, phase control and ac power switching
Equivalent to two SCRs placed in reverse parallel with each other
Lower current than SCRs

Triacs applications

Simple switch: using a typical switch and resistor, saves power
Dual rectifier: using capacitor and a variable resistor, outputs energy efficient pulses of current
AC light dimmer: using a C, var R and a diac, bulb ON/OFF with high frequency (same principle as pulses)
AC motor controller: same principle as above but with a transient suppressor

Four layer diodes: SCR without a gate lead, switch only DC

Diacs: pnp transistor without a base lead, switch only AC

Used to help SCRs and Triacs to trigger properly (avoid unreliable triggering due to temperature etc.)

Applications

Full wave phase control circuit: using C, var R, diac, triac
Circuit used to measure diac characteristics: using C, var R adjusted till diac fires once every half-cycle

12 aug

Transient voltage suppressors

Types: Bypass capacitor, zener diodes, transient suppressor diodes (TVS), metal oxide varistor (MOVs), multilayer varistor (MLTV), surgectors, avalanche diode, gas discharge and spark gap TVSs, polyswitches

TVSs

Unipolar, bipolar
Invisible unless transient occurs
Vbr >= 1.1 * Vrwm >= normal operating voltage of circuit
Fuse recommended along with
Applications

Inductive loads - protecting driving circuitry
Supply voltage over-protection
Op-amp applications
Transmission line
RF coupling (not clear)

MOVs

Voltage sensitive variable resistor
Bipolar only
Series filter inductor and fuse must along with
Can absorb very large power for a brief time or small power for longer time
Smaller leakage, many p-n junctions inside, work like heatsinks too!
TVS have no wearout, better clamp ratio, faster response time
Applications: Power supplies of computers, mains filters and stabilisers, telecommunication and data systems (power supply, switching), industrial equipment (control, proximity switches, transformers, motors, traffic lighting), consumer electronics (television and video sets, washing machines), automotive products (all auto and electronic systems)

MLTV

SMD form of MOV. Much quicker response time. Less degradation.

Applications: transient voltage protection for ICs and transistors, ESD and I/O protection schemes.

Surgector

Silicon thyristor technology. Similar functioning. Bi-directional.

Polyswitch

Opposite function - lets current flow normally, trips (stops current) after a breakdown voltage. Like fuse but reusable. Applications: low-cost, self-resetting solid-state circuit breaker, used to limit current in speakers, power supplies, battery packs, motors etc.

Avalanche diodes

Similar to a zener diode but very high breakdown voltage ~4000 V. Reverse biased.

Side effect: RF noise generation.

Integrated circuits

Analog/Digital, Analog+Digital
Package types: # of pins, power dissipation

13 Aug

Optoelectronics

When and electron changes energy levels a photon is emitted

A photon collides with an electron in the p-semiconductor side, and an electron will be ejected across the p-n junction into the n side. When a number of photos liberate a number of electrons across the junction, a large enough current is generated (e.g. at the base of a transistor to turn it ON)

LED applications / configurations

Current limiting / brightness control
Driving from AC using rectifier, capacitor and zener diode
LEDs in parallel - require a resistor each
LEDs in series
Voltage level indicator - using zener (when reverse breakdown voltage is reached, zener provides a wire path)
Polarity switching indicator
AC/DC polarity indicator - in AC, a red-green opposite to each other will appear yellow
Tri-color LEDs - green LED requires higher voltage so a diode is placed to bypass a resistor (that plays a part for red LED)
Blinking (flash) LEDs - can ON/OFF normal LED/transistor. Can handle 3-9 V without resistor

16 Aug

Laser diodes (LD)

Video on how laser diode works

Video on how CD/DVD works

Applications: CD/DVD/Blu-ray players, laser printers, laser fax, laser pointers, sighting and alignment scopes, measurement equipment, high-speed fiber optic, free-space communication, pump source for other lasers, bar-code and upc scanners and high performance imagers

Notes

Very delicate in terms of power/temperature/static discharge
Used with stable power source, feedback photo diode and beam focussing mechanism etc.
Photodiode (PD) gets light and generates current. More importantly it limits current by becoming a wire if the laser intensity rises beyond a point. Current (own generated / via an attached power supply) in 'reverse bias' direction.
Common configuration includes a PNP and an NPN transistor and several capacitors

Normal: PD is OFF, both transistors are ON, LD is ON
If spike: PD is ON (reduces current into LD by providing alternate path to power supply current and also by switching OFF/reducing current of PNP transistor). Collector of PNP transistor is put into base of NPN so current in latter also reduces. LD is attached with collector of NPN.

Various precautions needed, DIY power supply very difficult, use modules

17 aug

Photoresistors

Resistance decreases from megaohms (in dark) to kiloohms with light
Visible light/IR based
Applications: light meter, light-sensitive voltage divider, dark/light activated relay

Photodiodes

Become 'current source' (battery) hence current flows from Anode to Cathode (as if operating in reverse-bias configuration) - opposite to a normal diode
Mostly operates with additional battery since own current is small

Solar cells

Photodiodes with very large surface area
0.5V and upto 0.1A, response time 20 ms

Phototransistors

photo-bipolar, photo-fet
extra lead to supply additional V/I at base
Applications: light-activated relay, signal receiver, tachometer

18 aug

Photothyristors: Based on SCR / Triac

Optoisolators / Optocouplers

Closed pair - LED+ photodiode / transistor / thyristor
Slotted coupler - with a blocker in between
Reflective pair: used as object detectors, reflectance monitors, tachometers and movement detectors
Integrated (e.g. LED+phototransistor in an IC)
Applications: Level shifters, with amplifier (adding another power bipolar to increase current), pulse signal passed through with dc level shift, inverted/as-is
Solid-state relay: When control is ON, MOC3041 (IC with triac and zero-crossing detection) switches ON at every 0 crossing of the signal, keeping outside triac ON, passing the AC signal (from HOT to N)

Optical Fiber - Laser diode at source, photo diode at destination

19 Aug

Sensors

Precision, accuracy and resolution
Types: position, proximity, interial, pressure, optical, camera, magnetic, media, I/V, temperature, special (audio etc.)
Observer effect
Used in circuits as variable R/C/I or switch
ADC should be in-built
Calibration: resistor to ground (or base value) or use lookup table (actual behaviour graphs are complex)

Temperature sensors

Thermistor

NTC/PTC - resistance dec/inc (exponentially) with temp
Used as voltage divider, read Vout, calculate R and then T
R = R0 e^ [beta* (1/t-1/t0)]

Thermocouples

Best range
Two metal wires joined at both ends
Seebeck effect: when temperature difference at 1 junction (hot), voltage difference at other junction (cold)
V measured at hot junction along with Tcold gives Thot

Resistive temperature detector

Platinum coil on glass/ceramic
R varies linearly with T varies
upto 100*C

Analog IC (TMP36): Linear relationship, +/-2*C accuracy
Digital IC (DS18320)

Accuracy +/-0.5*C
1 wire serial interface
multiple sensors on same data line
power via data line

Infrared thermometers (MLX90614)

24 aug

Proximity and touch sensors

Resistive touch screen

voltage divider using resistors (video)
sensor at 4 sides, reading voltage, calculating x,y coordinates

Ultrasonic distance

ultrasound reflection
depends on object, sound speed in medium

IR optical sensor - light reflection
Capacitive sensor - hand becomes 2nd plate of capacitor, is grounded
Inductive sensor video

25 aug

Movement, force and pressure sensors

Passive infrared (PIR)

Detects change in IR heat, drives base of a transistor / relay
Open collector / open drain (used in I2C) video

Accelerometer

Microelectromechanical syste (MEMS)
Movement measured as change in capacitance
Mass is in between capacitor plates
F = k * (x-x0) = m*a
Video

Rotation

Video
Two pins, pulses in one direction are different from others hence both direction and number of degrees can be calculated
If clockwise, A (after every change) is opposite of B, if anti, A (after every change) = B

Flow

Wind rotates cups
proximity sensor (magnetic / optical) generates a pulse after each complete rotation

Force

Force sensitive resistor
Not very accurate, load cell more accurate

Tilt: metal ball on contacts, rolls off when tilted
Vibration and mechanical shock

weight at end of flexible piezoelectric material
resistor in parallel

Pressure: ICs

26 aug

Chemical sensors

Smoke

Radisotope sends ions (current) to detector continuously, smoke stops current
IR LED emitting light, smoke scatters it to fall on PD

Gas: heating element, catalytic detector (e.g. for methane), resistive divider
Humidity: capacitative, changes in dielectric constant of a polymer separating the plates

Other sensors

Light: photoresistors, photo diodes etc.
Radiation: Geiger-Muller tube: high voltage across cathode (casing) and anode (wire), current flows when radiation (e.g. for alpha particle)
Magentism

Hall effect. V appears when I passes through a conductor in a magnetic field
Magnet present or not, voltage proportional to magnetic field strength

Sound: Mic-->Amplify-->Rectify-->Low pass filter
GPS

receives time signals from multiple (as many as possible) satellites
use the difference in those times (due to the time for signals to travel) to calculate position

27 aug

Hands-on electronics

Schematic related

Can add waveforms / other such visible indicators of input / output e.g. 0010, 0011 to schematic
Check mention power ratings on schematic (to ensure you check)
Circuit simulator should be used before even schematic
Always mark polarity on silk screen (+/-) for polarised components

Safety

ESD mat and wrist strap
Neutral/ground has no role unless someone hot wire touches it (video from simply put)

28 aug

PCB related

Edge connector and I/O interfacing (gold plated fingers): one way to join multiple boards together
IC/transistor sockets on PCB: so you could replace if needed
Heat sinks
Can add needle nose plier / heatsink clips to save component while soldering
Casing related notes

Standoffs to separate PCB from casing
Strain relief for cables
Grommet around edges of holes
Frequently used switches etc. in front
Seldom used switches etc. in back
If lot of heat is being generated, add blow fan
Medium heat: holes in box can help
Major heat producing components (e.g. power resistors/transistors) in back. Connect them to heat sink through back panel
Heat sinks with fins should be in vertical direction
If >1 board, align vertically for better ventilation

29 aug

Multimeters

Analog

D-arsonval galvanometer
Resistors to control current and calibrate
Bridge rectifier to measure AC

Digital

Signal scaler - attenuator, range selector
Signal conditioner - converts to DC
ADC converter
Logic/decoders/counters
More accurate but more prone to noise
20-33% error due to internal resistances

Oscilloscopes

Only voltage measure
Cathode ray tube with vertical and horizontal deflection plates
Analog applications

Check potentiometer for static noise
Pulse measurements - rise/fall time, pulse width, delay, tilt, overshoot
Measuring impedances - signal reflection due to different impedances

Digital applications

I/O relationships
Clock timing relationships
Frequency division relationships
Check propagation time delay
Check logic gates

30-31 Aug

Oscilloscope, probes, Lab, general purpose function generators, isolation transformers etc.

12-16 Sep

Operational amplifiers (Op Amps)

High performance differential amplifiers
Non-inverting input (V+), inverting input (V-), 2 DC supply leads (+Vs, -Vs), 1 output (Vout), few specialised leads for fine tuning
If V+>V-, output saturates towards +Vs, otherwise -Vs
Negative feedback: Vout = -(Rout/Rin) * Vin
Applications of negative feedback: voltage regulator, I to V converter, V to I converter, oscillator, mathematical functions (+/-/*/integrator/differentiator), waveform generator, active filter, active rectifier, peak detector, sample-and-hold circuits
Positive feedback: opposite effect, less used, special comparator circuits
Water analogy: useful, infinite input impedance, 0 output impedance
Op-amp = high input-impedance differential amplifier+high-gain voltage amplifier + low-impedance output amplifier
Vout = A0 * (V+ minus V-); With negative feedback V- becomes f*Vout
Rule 1: A0 = infinite (ideal), 10^4 to 10^6 (real) [JFET is better than bipolar]
Rule 2: Rin = infinite (ideal), 10^6 to 10^12 (real); Rout = 0 (ideal), 10 to 1000 (real)
Rule 3: I = 0 (ideal), 10^-12 to 10^-9 (real)
Rule 4: Negative feedback is such that V+ = V-
Negative feedback applications

Buffer (unity gain amplifier): Rout=Rin (Rsource), useful for circuit isolation applications
Inverting amplifier: resistor = R1||R2 b/w non-inverting & ground to minimize input bias current offset errors (especially for bipolar )
Non-inverting amplifier
Summing amplifier: Rout=R1=R2=R3, another inverting unity gain amplifier in front
Difference amplifier
Integrator: capacitor instead of Rout, sq wave-->saw-tooth, add Rout for stability
Differentiator: capacitor instead of Rin, saw-tooth->sq wave, add Rin & another C at Rout for stability, noise & phase shift problems

Positive Feedback

Vd (difference b/w V+ and V-) is not 0 in this case
Switches state when Vd approaches 0
+ive and -ive threshold, hysterisis voltage
Quite jazzy signal into square wave
Comparator circuit, more immune to noise

Real kind of Op-amps

General purpose
Precision: high stability, low offset voltages, low bias current; often JFET but introduces phase shift if input too close to negative supply
Pros and cons of JFET and Bi-polar
Programmable Op amp

For low-power (battery) applications
characteristics that can be altered via program: quiescent power dissipation, input offset and bias currents, slew rate, gain-bandwidth product and input noise

Single supply op amps: output cannot go -ive, not for ac coupled audio signals (output is clipped)
Audio amplifiers

designed to operate best in audio frequency spectrum 20-20k Hz
used in sensitive pre-amplifiers, audio systems, AM-FM radio receivers, servo amplifiers, intercom and automotive circuits

Op amp specifications

CMRR (common mode rejection ratio): how well the op amp rejects common mode signal (e.g. noise applied to both inputs)
Differential input voltage range
Differential input impedance
Input offset voltage
Input bias current
Input offset current
Voltage gain: gain drops to 1 at unity-gain frequency (1-10MHz)
Output voltage swing
Slew rate
Supply current

Power op amps

Require dual polarity supply (or split a supply by putting GND in middle)
Or use single supply op amps but they clip the output when supply is negative (e.g. in ac)
Apply dc offset using a voltage divider at input, use capacitors at input and output to filter out dc. Why C2 not clear.

Practical notes

Reverse polarity protection - using diode at -Vs
Oscillation protection - using capacitors at both Vs and -Vs
Destructive latch-up protection

using schottky diodes at both Vs and -Vs
Current limiting resistors may also be added
Avoiding latchup in CMOS chips

Voltage and current compensation

Put POT in the pair of offset null terminals (of the IC e.g. 741C)
Short inputs, apply Vin and adjust the POT till Vout is 0
For input bias current, put Rcom = R1||R2 at non-inverting terminal
Current compensation is more needed in bipolar

Frequency compensation

Typical open-loop gain is 10^4-10^6
Gain drops to 70% (3dB) at breakover frequency (fb) and to 1 at unity-gain frequency (ft) ~ 1MHz
To frequency compensate, add RC network between op-amp's frequency compensation terminals
Or buy one that is internally compensated

Comparators

Which of the signals is bigger OR when the signal exceeds a reference
Simple inverting/non-inverting op amps can be used with V+/V- GND
Pot can be added to calibrate Vref (from +Vs for e.g.)
Special comparator ICs are different from op-amps

uses positive feedback (never use -ive feedback)
not frequency compensated
much larger slew rates (for high-speed switching)
internal transistor whose C is connected to Vout, E is GND; when V+<V-, transistor is ON so Vout = 0; when V+ > V-, transistor is OFF so Vout = +Vs (or a fraction of it)
External pullup resistor needed between +Vc and Vout
Vc is the output threshold and is different from Vs
Used in ADCs

Comparators with hysteresis

To add a cushion region that ignores small deviations
Adding positive feedback (via R3) leads to two threshold voltages
Inverting and non-inverting
Rule: Rpull-up < Rload, R3 > Rpull-up

Single supply comparators

emitter and negative supply connected and grounded
with and without hysteresis

Window comparator

Output is high (or low whatever is desired) whenever input voltage is within a pre-determined range of voltages ('window')
Using 2 comparators with Vin applied at one's V- & other's V+

Voltage-level indicator

Using multiple comparators (V- of each is Vin) and LEDs
V+ to each using resistor divider (fraction of Vs)
As Vin rises, lower comparator's Vout is grounded first (LED turns on)

Instrumentation amplifiers

Able to amplify very small voltages (medical application - heartbeat)
very good CMRR
Circuit / formula not clear

Comparator applications

Op amp output drivers (for loads that are on/off): LED / buzzer / transistor / mosfet / transistor + relay
Comparator output drivers: pullup, TTL/CMOS circuits
Op amp power booster (AC signals): 2 transistors (npn and pnp)
V to I converter: simple load at Vout
Precision I source: Mosfet + transistor in front
I to V converter using photoresistor/photodiode/phototranssitor+relay
Overvoltage protection (crowbar): input at V+, zener at V- (ref), driving SCR
Programmable-gain Op amp: R2 is a collection of resistors in parallel ON/OFF using digital switches
Sample and hold circuits: switch and capacitor, -ive feedback
Peak detectors: capacitor and diode, -ive feedback, smart way to avoid diode 0.6V drop
Non-inverting clipper amplifier: pair of zeners in parallel to R2
Active rectifiers: using diodes to clip as well as instead of R2, can take output from both sides of diode (to avoid 0.6V drop)

17-19 sep

Filters

Low-pass, high-pass, band-pass, notch
Lots of applications e.g. dc power supply, radio send/receive, audio speakers
Passive (100-300 MHz)

+can operate on RF
-large components

Active (0-100KHz)

+easy to make (no inductor)
+desired i/o impedance can be provided independent of frequency

Attenuation graphs
Terms

-3dB frequency

+3dB = double power = 1.4 * V / I
-3dB = 1/2 power = 0.7 * V / I

Center frequency (f0): for bandpass filters = sqrt (f1*f2) for wide band, (f1+f2)/2 for narrow band
Passband: <3dB attenuation (good signal)
Quality factor: bandpass f0/(f2-f1), notch (f2-f1)/f0, called null frequency

Basic filters

6dB per octave (i.e., 4 times attenuation by next frequency that is double the current), is not enough
Steeper falloffs and flatter bands are needed
Combining a number of '6 dB per octave' filters won't work

Filter design techniques

Butterworth: flat band, steep fall, easy to make, most popular
Chebyshev: steeper fall, ripple in band
Bessel: less steep, less flat, No delay distortion (more accurate reproduction of modulated signals)

Practical filter designs

Passive low-pass (PL)

Normalisation: f3dB = 1 rad
Pick response curve: Butterworth
Determine # of poles: per requirements, use graph
Create a normalised filter (pi / T) - values from table
Frequency and impedance scaling

Passive high-pass (PH)

Flip curve to make PL, design as before and flip (C-->L, L-->C)
Choose T (with more inductors) since it will be transformed to pi

Passive bandpass (PB)

Wide band (f2/f1>1.5): PL+PH
Narrowband: treat bandwidth as f, complex procedure

Passive notch (PN)

similar to PB-narrowband but use PH as base

Active low-pass (AL)

Different table for values

Active high-pass (AH)

Create normalised low pass
exchange R with C, C with R

Active band-pass (AB): use given circuit
Active notch (AN): use given circuit

20-24 Sep

Oscillators and Timers

Intro: endless applications, different design principles, pros and cons of each
RC relaxation oscillators

Square wave

using C connected to V-, R1, R2, op amp
If op amp's output is +15V, C begins charging upto +15V, when it reaches +Vt (threshold set via R2 into V+), Vout flips tp -15V, C starts discharging till -Vt and cycle repeats
time constant R1C, period 2.2R1C not clear

Sawtooth wave

C as feedback to V-, PUT in parallel to it
PUT discharges C when it reaches desired level
POTs/voltage divider to adjust V-/Vref (impacts frequency)
POT at PUT's gate voltage (impacts amplitude)
C charges in a linear manner (small portion of an exponential curve)

Square + Triangle waves

2 op amps: 1 with C as -ive feedback, 1 with R as +ive feedback
Output of op amp2 = input (V-) of op amp 1

Using other than op amps

UJT based: simple V divider with C, 3 waveforms (one across C, 2 pulses of B1 and B2 of UJT)
CMOS schmitt trigger inverter: square wave
Digital oscillator using CMOS inverters

555 Timer: Astable (periodic waveform)

C=0V —> comp2 o/p high —> S=1, R=0 —> Qbar low, O/p high (cap charge starts)
C>1/3Vcc—>comp2 o/p low—>S=0, R=0—>Qbar/O/p no change
C>2/3Vcc—>comp1 o/p high—>S=0, R=1—> Qbar high, O/p low (transistor ON, cap discharge starts)
C<2/3Vcc—>comp1 o/p low—>S=0, R=0—>Qbar/O/p no change
C<1/3Vcc—>comp2 o/p high—>S=1, R=0—>Qbar low, O/p high (transistor OFF, cap charge starts)
Tlow = 0.7R2C1, Thigh=0.7(R1+R2)C1
Thigh is always > Low (discharging is faster than charging)
To make Thigh<Tlow, add a diode across R2 and make R1<R2 (charging faster than discharging)
R/C low - frequency high (small components->faster charge/discharge)
R1: 10k - 14M ohm, C1: 100pF - 1000uF (same in monostable)

555 Timer: Monostable (one shot timer)

Cap=0, trigger=Vcc (pullup), comp1 (V+=0, V-=2/3Vcc), comp2 (V+=1/3Vcc, V-=Vcc), R=0, S=0, FF=1*, Out=0, Transistor=ON
Cap>0 (started charging), trigger=0 (GND), comp1 (V+>0, V-=2/3Vcc), comp2 (V+=1/3Vcc, V-=0), R=0, S=1, FF=0, Out=1, Transistor=OFF
Cap>2/3Vcc, trigger=Vcc (pullup), comp1 (V+>2/3Vcc, V-=2/3Vcc), comp2 (V+=1/3Vcc, V-=Vcc), R=1, S=0, FF=1, Out=0, Transistor=ON
Bold states are momentary
*FF=1 initially as it retains previous state (it's only stable state)

RS flip flop truth table

5. 555 timer types: Bipolar and MOSFET (indicated with 'C'); single/dual/quad

6. Tip: 0.01uF between pin 5 and GND, 0.1uF between pin 8 and 1

7. Simple 555 applications

Relay driver (delay timer): drive a relay from 555 output
LED, lamp flasher and metronome: similar config, driving from Vout via a transistor
Voltage controlled oscillators: NE566 - triangle and square wave; special ICs 8038, XR2206 can generate sine, triangle and square wave

8. Wien-bridge oscillator (helpful link)

Using op amp (V+=V- rule 4), RC in series and in parallel
Choose R and C values so that only resonant frequency (at which R and C will oscillate) will pass on with a gain of 3
Variation has V+>V-, includes pair of zener diodes & POT to adjust V- and prevent saturation
Twin-T oscillator

T like arrangement of Rs and Cs
2 networks (one low and one high pass) joined together
Very precise band (narrower than Wien-bridge) of freq passes through

Both wien-bridge and twin-t can generate sine waves

9. LC oscillators

Used for high freq (<=500MHz) sine waves (e.g. in RF applications)
Not good at low (e.g. audio) freq
Basic circuit

Comparator, +ive feedback, LC tank circuit in parallel to feedback
Comparator supplies just right energy to ensure oscillations don't die
Fourier component at resonant frequency provides energy - not clear
Practically, for high frequencies, use transistor amplifier (instead of comparator) but need to add 'phase shifting network' between output and input

Harley

Using JFET: split L coil in parallel with variable C
Using bipolar: base needs voltage, load across secondary coil

Colpitts

Freq range wider (than Harley), more stable
Split capacitors in parallel with variable L
Can add another variable C in parallel

Clapp

Exceptional freq stability
Variable Ct (<<C1&C2) in series with L (series resonant with L)
Ceffective = Ct (since C1, C2 and Ct are all in parallel)
Lt and Ct determine resonant freq

10. Crystal oscillators

Much more stable (0.01-0.001%) than RC (0.1%) and LC (<=0.01%)
Equivalent circuit: C0 in prallel with R1, C1, L1 in series
Impedance vs freq graphs, series resonant (fs), parallel resonant (fp)
Fundamental (f0) and Overtones (odd multiples of f0)
Usage instead of LC tank circuit: can use in series or parallel (fs or fp)
Applications: basic, pierce, colpitts, CMOS inverter

11. Microcontroller oscillators

Stores waveform in memory and play using DAC
8-pin with built-in clock is better than 555 (fewer external components)

25-27 Sep

Voltage regulators and power supplies

2 types: step-down transformer based & switch-mode power supply
Transformer (inductors)-->Rectifier (diodes)-->Filter (caps)-->Voltage regulator (IC+caps)
Voltage regulator removes spikes/dips & mitigate change in I due to chane in load resistance
Fixed voltage regulator ICs: LM78xx (+), LM79xx (-)
Adjustable: LM317 (+), LM337 (-), TL783 (+) - high range
Flyback diode needed to avoid reverse biad e.g. load/output cap discharges slower than input cap
LDO (low drop out) voltage regulators: LM2940. Can run on low Vin (as compared to Vout) and hence is cooler
Applications

Car battery voltage regulation
Current regulator
12V battery charger

Dual polarity

Transformer with center tap in secondary coil gives both + and -
Resistor divider to adjust in LM317/337 (+/-1.2-35V). 24-0-24 config
No adjustent in 7815/7915
Fixed +/- 12V: 7812/7912
Heat sinks necessary

Adapter power engage, battery power disconnect circuit
Ripple rejection in voltage regulators

Vripple (rms/pp) should be <+/-0.25% of Vout (less the better!)
Ripple rejection factor is measured in dB
7805 has 60dB i.e., ripple reduced by a factor of 1000
Add bypass capacitor e.g. in LM317 to achieve 80dB (from 65) i.e., rpple reduced by a factor of 10000

Loose ends

Line filter (LC) & transient suppressor (back2back zener diodes)

before transformer
filter out high freq interference, spikes, RF emission by supply

Overvoltage protection

after regulator (if it fails)
Crowbar: Zener + SCR (needs reset after trigger)
Clamp: Zener + transistor

Bleeder resistor

across output
across inout with cap (transient suppressor)

Switching regulator supplies (switchers)

Oscillator (steady pulse) & error amplifier feed into PWM
Error amp: higher if o/p is lower (than Vref), lower if o/p higher
PWM: ON for lower duration if error amp is low, higher if high
Inductor to store energy & drive load when PWM is off
>85% efficiency (as compared to <50% for liner regulators)
556 dual timer (oscillator + PWM modulator) + UA723 (error amp)
Step-dwn/up/inverting (video on how inductor steps up voltage)
LM2575: adjustable & fixed versions

Switch mode power supplies (SMPS)

60 Hz transformer out but high freq transformer instead of inductor (smaller and cheaper)
another isolation element b/w error amp and pwm
switching ripple voltage: external high current low pass filter can be added

28 Sep

Digital electronics

Number formats: binary, decimal, hex, octal, BCD, 2's complement
Logic gates applications

Enable / disable control
Waveform generation

Exclusive gates: De Morgan's theorems
To simplify circuits

Boolean algebra
Bubble pushing (add->or, or->and, remove bubbles, add where none)
NAND / NOR: universal gates
SOP / POS: SOP is easier, easy to understand/implement can be different
AND-OR-Inverter ICs
Karnaugh maps: online calculator

Combinational ICs: 4000, 7400 series
Multiplexers (data selectors) - using n control lines to select 2^n data (input) lines, 1 output
Bilateral switches: using n lines to select n inputs passed as n outputs
Demultiplexers

input routed to one of 2^n outputs using n selection pins
74HC139 (4+4), 75xx154 (16)
unselected output = 1

Decoders

similar to demux, just makes the output(s) 0 or 1 (741S138)
one format to another: BCD2Dec, Dec2Hex
BCD27 segment (7447): lamp test, ripple blanking inout/output

Encoders

one input to multiple output pins
74LS147: Dec2BCD, negative true logic
Priority: if multiple pressed, only highest is output, extra circuitry for this
74LS147+inverter+7447: Dec>BCD>7segment
74148: Octal to binar priority encoder
74184/5: BCD2Binary encoder, bits arranged/interpreted as per need

Binary adders: half, full; XOR+AND
Subtractor

For one number, do 2's complement using XOR with 1 (button=1) & Cin=1, then ad to other number (kept as-is)
Same circuit can be used as adder (button = 0)

Comparators & magnitude comparator ICs: A=/>/<B
Use ICs instead of gates: FPGAs are faster (raw hardware + some software flexibility), uC can be cheaper but bit slower (because of software)
Logic families: TTL, CMOS, mostly CMOS is used: less space, simpler construction, higher noise immunity, less power consumption but slower
Logic ICs power management

Decoupling caps must: both transistors in totem-pole can be ON for a brief moment during logic low-->high or high-->low drawing larger current from power supply, resulting in spike
Don't let unused inputs floating
CMOS IC can get damaged if power at input pins but not at Vcc/GND

SR flip flop (set reset)

Cross NOR, Cross NAND (more popular in the book)
States: Set, Reset, Hold, Not used (because of race condition/unstable/unpredictable results)

SR flip flop applications

Switch debouncer

when a switch is closed, the metal contacts bounce a number of times before coming to rest due to inherent spring like characteristics of the contacts, resulting in false triggering
SR FF avoids that by storing the initial switch contact voltage while ignoring (by going into 'hold' state) the trailing bounces

Latched temperature or light alarm

Variable resistor divider followed by SR FF
Buzzer attached to Q (bar), reset button at Q

Level triggered SR FF (beginning of clocked FFs)

synchronous or clocked FFs
2 NAND 'enable' gates in front of SR FF - each has 1 input as CLK
During the clock ON, inputs (S and R) are passed on to outputs (Q and Q bar)
have to keep S and R at desired input state throughout the CLK ON time

Edge triggered SR FF

Samples the inputs only during the clock edge (+ive or -ive)
CLK passes via a 'pulse generator' that splits CLK into 2 inputs one goes via a 'NOT gate with propagation delay' (+ive)
For -ive edge trigger, another NOT gate in front of CLK

Pulse triggered SR FF

Master slave SR FF
Two SR FF arrangements: master with CLK then slave with CLK bar
During +ive edge, master gets cocked (liek a gun), during -ive edge, slave gets triggered
CLR and PREset at slave - exactly how they work not clear

SR FF ICs

74LS279A: switch debouncer, quad extra input, using software instead is free!
4043 (NOR), 4044 (NAND): quad

D type flip flops

S=D, R = Dbar: simplified truth table, no race condition/hold
Clocked level triggered D FF: CLK introduces hold
74HC74: dual d type positive edge triggered FF with preset and clear
D input must be fixed high/low at least one setup time (~70 ns) before the positive clock edge
Also comes in pulse triggered variety
Applications

Stop and go: green LED at Q, red at Qbar, one ON at a time
Divide by 2 counter: +ive edge triggered, ignores -ive edge
Synchronizer: keeps the external control signal in synch with system clock. When it goes through FF, it is effective only during the next clock pulse edge (not as and when it comes)

Quad D FF IC
- 74HC75 (asynchronous without clock)
- 4042 (synchronous, with clock)
- application: 4 bit data register
Octal D FF IC

74HCT273: 8 bit data register, edge triggered

JK flip flops

‘Toggle’ as 4th state at 11
Extra connection (cross coupled feedback) from Q to R (K) & Qbar to S (J)
No level triggered version
Mostly edge triggered
Pulse triggered exists but has problem of ‘one’s catching’ (catches glitches via electrostatic noise & treats it as real data. Not much of a problem if CLK duration is small)

JK FF applications

Ripple asynchronous counter (0-15) / frequency divider by 2/4/8/16

4 JK FFs: o/p of one = CLK of next
J=K=1 (toggle only) for all
Q0=LSB, Q3=MSB
4 clock pulses each with f=1/2 fprevious form a binary number pattern (0000-1111)
To reverse count, use Qbar instead of Q

Ripple asynchronous counter (0-9) then stops and activates an LED

Q0 & Q3 via a NAND gate to sink current of LED
CLR to restart

Synchronous counter

Each FF has propagation delay that adds up in previous asynch config (output of one = clock of next) ~30*4 = 120 ns
Same clock for all
Output of all previous (ANDed together) is input of next
2 AND gates for 0-15 counter

Practical timing considerations

Setup time: time input must be held before the active clock edge ~20 ns
Hold time: time input must be held after clock edge ~0 ns
Tplh: propagation delay from clock trigger to low-to-high output swing
Tphl: propagation delay from clock trigger to high-to-low output swing
Fmax: max clock frequency allowed
tw(L): minimum clock pulse width (low) allowed ~20 ns
tw(H):minimum clock pulse width (high) allowed ~20 ns
Preset or clear pulse width: minimum width of the low pulse

Clock generators (astable multivibrators)
- mostly a capacitor is used with cmos inverters (74HC04)
- 555 timer needs another JK FF to generate square wave + enable switch (with debouncer)
Monotstables (one shot)
- 74121, 74123 (retriggerable)
- applications: timde delay, timing & sequencing
- 555 can also be used in mono mode (is cheaper)
One shot / continuous clock generator
- 74121 + 555 with a switch (with debunker) in between
Auto power up clear
- using RC network
- After switching power ON, CLR remains low till capacitor charges to desired voltage
- Schmitt trigger inverter to make a square wave (clean OFF of CLR)
Pullup and pulldown resistors
- pullup most common because it wastes less power, 10k work for most
- see data sheet to choose value that is
- pulldown resistor value is usually much less (still it wastes more power when the switch is closed)
Counter ICs
- Asynchronous 4-bit ripple 7493, 7490, 7492
Synchronous counter ICs (same CLK, less propagation delay)
- 74193 (0-15) presettable
- 74192 (0-9) similar
- 74190 (0-9) / 74191 (0-15)
- 74160, 74163 (0-15)
- 74LS90: divide by X counters (configs not clear) page 787
Counter with display
- microcontroller multiplex: less wires
- segments of each digit are linked together (same D0-D7 going into each digit)
- separate enable pins for each digit, whichever is enabled is displaying the number decided by D0-D7
- flashes LEDs fast, appear continuous multi-digit display
- ICM7217A: 4 digit up/down counter with LED display
Clock pulse generator (60/10/1 Hz)
- using AC line (115V, 60Hz) with transformer (12.6V, 60Hz), zener diode (3.9V)
- Schmitt trigger inverter (0.2-3.4V output, 60Hz) (to make proper square wave)
- followed by divide-by-6 counter (10 Hz), followed by divide-by-10 counter (1Hz)
Shift registers
- serial-in:serial-out, serial-in:parallel-out, parallel-in:serial-out, parallel-in:parallel-out
- parallel needs 1 pulse to go out/in, serial x-bit needs x pulses
- ring counter (output of last FF = input of first)
- Johnson shift counter (output of last FF inverted = input of first)
- 7491A: serial-in:serial-out, 2 inputs (1 data, 1 ctrl), application not clear
- 74164: serial-in:parallel-out
- 74165: serial or parallel-in:serial-out
- 74194: universal shift register (4 bit). any mode in, any mode out
- 74299: 8 bit universal shift register with storage and 3 state interface
Simple shift register applications
- 16 bit serial to parallel converter: two 74164 ICs, Q7 of 1st into Q1 of 2nd
- 8 bit serial to parallel: 74164 (CLK) + 74NCT273 (parallel to parallel, CLK/8)
- 8 bit parallel to serial: 74165
- re-circulating memory registers: 74194 (p->s mode)
Analog / digital interfacing
- ON/OFF triggering
Using logic to drive external loads

how much current the load requires
how much current the logic gate can source / sink
if Iload > Igate, can use a higher power transistor in between

36. Using logic to drive external loads

how much current the load requires
how much current the logic gate can source / sink
if Iload > Igate, can use a higher power transistor in between

37. Analog switches

4066B, AH0014D, DG302A
functionality: DPDD/DPST/number of in/out
supported voltage levels
switching speed
applications: modulator/demodulator, digital controlled frequency circuits, analog signal gain, ADC, analog device on/off

38. Analog multiplexer / demultiplexer

data selector / data distributor
4051B

39. ADC and DAC

ADC applications: data acquisition, digital sound recording, display
DAC commonly used to control the gain of an op amp: digitally controlled amplifiers, filters, wave form generator, modulator, trimmer replacement, process control and auto calibration circuits, mp3/dvd/cd player
sampling frequency, resolution (eg. 4 bit)

40. DAC configurations

simple binary weighted

74HC4066+resistors+op amp with -ive feedback
not practical if > 4 bits
many different resistors needed

R/2R ladder network

only 2 resistor values needed

41. Integrated DACs

DAC v MDAC (multiplying)
MDAC gives current output, Vref is varying, has wider V range, faster switching
Digital Vref (fixed) can also generate a waveform by varying digital code
ICS: DAC0808 (8 bit): unipolar and bipolar operation. Bipolar uses 2 op amps

42. ADC: many techniques

successive approximation

comparator —> SAR —> DAC —> Output register (octal D FF)
fast conversion time (10-300 uS), simple circuitry
set MSB = 1, if corresponding Voltage (calculated by DAC) > Vin, make MSB=0
do same with all remaining bits
control signals: start conversion, conversion complete

parallel encoded / flash conversion

7 comparators, same Vin to all
each denotes a voltage
Output into 74F148 (octal to binary priority encoder: takes only highest number)
74F75 (FF) at end
If a digit (x) is low & next (y) is high, voltage range is between Vy & Vx
Output is only a range (not exact value)

43. LED displays

7/14/16 segment, 4*7 / 5*7 dot matrix
common anode with 74LS47
common cathode with 74HC4511
MM5450: can drive four ‘7-segments’
multiplexed using a microcontroller and 74HC4511: flashing 4 ‘7-segments’ quickly so it appears it is a 4-digit (continuous) display. Enable one at a time & provide digital code to display
simple alphanumeric pda54-11
smart alphanumeric hpdl-1414

44. LCD displays

lower power consumption, less switching speed (40-100 ms)
external lighting used! sunlight / backlight
74HC4511+XOR gates —> 7-segment
CLK into XOR gates & 7-segment back electrode / plane (BP)
front electrode: individual for each segment
If front=0, when CLK=BP=1 (potential diff with BP): we see the char
If front=1, when CLK=BP=1 (no potential diff with BP): no char
Display remains as-is when clock goes down, just polarity is reversed:

when CLK:1->0, BP:1->0, front XOR:0->1, char remains displayed
when CLK:1->0, BP:1->0, front XOR:1->0, display remains blank

Physics

if no potential diff, crystals rotate light by 90* so overall silver against silver
if potential diff, crystals don’t rotate, so the 2 polarisers absorb all light, segment appears (dark against silver)
nematic crystals 90*, super twist nematic display 270*: better contrast, viewing angle

Driving LCDs

CD4543B: input->latch->7-segment decoder->display driver. Disable latch to prevent new data
MM5453: 40 pin, can drive 4.5 digits

Multiplexed LCDs
Dot matrix LCD (HD44780)

can read from LCD too
writing happens when enable goes from high-->low
enable needs a switch debouncer if operated with switches (not common)
CGROM - to store fixed 192 chars
DDRAM - to store current display chars (80)
CGRAM - to store custom chars (8)
Instruction set, 4-bit transfer etc

45. Memory devices

Basic understanding with diodes matrix addresses (n lines (rows)=2^n addresses/words) and m bits (columns) words
Programmable ROM: transistor (bipolar / mosfet) at each cell

One time programmable ROM

Mask ROM (MROM): manufacturer makes connections (diode/transistor)
PROM: you can make connections by blowing fuses once

Re-programmable ROM

EPROM

extra floating gate (below control gate) in MOSFET
initially all 1s
hot exlectron injection (12v) to give negative charge to floating gate (out of circuit programming)
erase using UV light on quartz window (whole memory erase)

EEPROM

2 transistors. 1 to store data, other to clear charge from 1st's floating gate
in-circuit programming, can erase selective cells
applications: TV tuners, uC main program & non volatile data

Flash memory

combines EPROM (high storage density) & EEPROM (in-circuit programming)
some variants erase full chip only
faster read-write and erase times
applications: uC main program, digital camera, music players, phones etc.

Serial access memory

parallel direct connections to address and data bus can lead to big impact if uC makes mistakes
eprom / eeprom can be used in serial mode ex. I2C (SDA/SCL)

RAM

volatile, much faster read-write, not limited r/w endurance cycles (10000 for eeprom)
Static RAM (SRAM)

Flip flops
bits remain stored until overwritten / power off
low power consumption
higher speed and ease of use
used where less memory is needed e.g. uC cache
To make SRAM non volatile (add battery / backup eeprom)
SRAMs can be combined (expanded) for higher storage

Dynamic RAM (DRAM)

capacitor
bits disappear within milliseconds if not refreshed or supplied with periodic clocking to replenish capacitor charge (lost to leakage)
more data storage per unit area
used where MBs of memory needed (e.g computer memory modules)
# of address lines cut in half by multiplexing
refresh every 2ms: by reading/writing/'RAS only' (line by line scan)
DRAM controllers handle this (autorefresh)
Computer memory in SIMMS and DIMMS packages
DDR3: 240 pin DIMMS
Extended data out (EDO): 10-20% faster
Synchronous DRAM (SDRAM): synch memory with PC clock (25% performance rise)
Double data rate SRAM (DDR): able to read data on both rising and falling edges of the system clock
Rambus DRAM (RDRAM): uses a high bandwidth channel, ~10 times faster than DRAM

20 Nov

Microcontrollers

ATTiny / PIC
Harvard architecture: separate memory for program and data
Bank switching: using same memories for different purposes (defined schemes)
3 approaches to program

Program in C, compile (on PC), send to uC (using hw programmer)
Program in C (on PC), send o uC which has an interpreter to compile & run. Takes more resources on uC but faster to test
Program in C (on PC), send to uC, bootloader on uC (runs at every reset) detects new program and replaces as uC main program (arduino/esp)

Interfacing with microcontrollers: digital, analog, serial
Digital interfacing

manual switches with pullups
pullup resistors considerations:

choose pull up such that current consumption is minimal while taking care of the signal strength
should be strong enough to be interpreted correctly and not confused with noise
Depends on noise in environment & lead length
Internal pullups are generally high

multiple switches using 1 analog input (voltage divider)
matrix keypad (parallax link)
switch debounce using software (arduino code link)

7. Analog interfacing (input sensors)

if i/p voltage is > uC expected, add resistor V divider, add zener to fix max V
handle sensor hysterisis using s/w
uC reliably provides ~20mA source/sink current as o/p
derate by 25% for production poduct
to drive higher load, use transistor (bipolar/mosfet)
mosfet has low drain-source R when ON, high R when OFF, high i/p Z so less current needed/drawn from uC
Arduino 40 mA per pin, max 200mA per chip
if inductive load (e.g. relay), separate supply recommeded
Motor control using PWM

control motor speed by adjusting duty cycle
74HC07 buffer: stable o/p and high noise immunity
motor bi-directional control: H-bridge with 4 mosfets (2 npn, 2 pnp). 2 mosfets ON at a time (fwd/back)
IC should have thermal shutdown to prevent overheating
servo motor: duty cycle pulse (control signal) determines direction. 1ms pulse: 1 direction, 2 ms other
stepper motor: many coils to be energised in correct sequence. uC (step sequence)—>Driver IC (ULN2803)—>Transistor array for high power loads—>Motor

Detecting sound

mic—>2 comparators (LM324)—>uC—>power transistor (as amplifier) with speaker as load (high current due to 8 ohm speaker)
uC ADC is not very fast. Only for primitive loads
piezoelectric speaker can be driven directly by uC pin
no point amplifying square wave (sounds harsh)
generate sine wave: using pwm not good quality, use DAC (R-2R)

8. Serial interfacing

1 wire

send command or set bits in register
since no CLK, frequency/pulse width translated into bits
different pulse width to send 0 (60uS) & 1 (15uS)
each CMD preceded by a reset
temperature sensor (DS18B20)
parasitic mode - gets power also from uC, 5 or 3.3v, pullup 4.7k
when no data transfer, capacitor charged, it drives device when data is transferred

2 wire (I2C)

actually need 4 wires: VCC, GND, SDA, SCL
5 or 3.3v, pullups 4.7k
>1 master possible, can change roles
SDA/SCL are open drain & tri-state : 0, 1, high impedance (tri-state)

upto 80Mbps
only 1 master

UART

no CLK
agree baud rate & bits (8N1)
RS232 (Tx/Rx)
TTL logic levels (-ive and +ive)

Voltage level conversions

easy in SPI and UART: different lines for 2 directions of comms
only 5v(uC)->3v (device): Tx->Rx conversion needed
I2C & 1 wire: ICs TXS0102, MAX3372, PCA9509, PCA9306
Link from NXP on voltage conversion in I2C

9. LED displays

multiplexing, charlieplexing
control intensity / color (i.e., current) of RGB LED using PWM instead of analog control

Programmable logic

PAL - programmable array logic
CPLD - complex programmable logic device

configurable logic cells
uses sum of products arrangement of gates

FPGA - field programmable gate array

uses lookup tables
hundreds of thousands of logic cells

HDL - hardware description / definition language

Verilog / VHDL

Expensive customizable hardware
used for prototyping for high volume production runs
Xilinx and Altera are major companies making these

Motors (23-25 nov)

DC motors

stall current = max current when the motor is applying max torque (rotational force) & not able to move
Link
Speed control

some oscillator --> power transistor / scr / mosfet
bipolar not good
UJT relaxation osc + SCR
CMOS NAND gate osc + MOSFET
555 timer (astable) + MOSFET
uC (PWM) + MOSFET (add buffer to isolate uC from inductive load)

Direction control

manual DPDT switch
transistor driven DPDT relay
complementary (npn-pnp) pair of bipolar power transistors
H-bridge with bipolar

2 pins: each can enable, control speed and direction
at a time give pwm to only 1 pin

H-bridge with MOSFETs

separate 'run enable' & 'change direction' pins

motor driver IC: LMD18200, L293D

RC servo motors

Link 1, Link 2
AC/DC, Brush/Brushless, Synch/Asynch
commutator: mechanism that supplies alternate current
AC is brushless (generally)
speed ~ frequency & # of poles
speed of rotator < speed of change in magnetic field
Precise positioning
DC Motor + gear assembly + position sensing device (feedback circuit/POT) + control circuit
uC / 555 timer give control signal, when it moves POT also moves
3 leads: VCC, GND, control
send control signal (PWM), internal POT will tell control circuit the actual position, control circuit will compare actual position with signal & will move motor one way or the other
Internal POT can be replaced with fixed resistor voltage divider to achieve 360* turn
model airplanes (remote control servo) get control signals via radio waves

Stepper motors

Link 1, Link 2 (detailed explanation of bipolar etc.)
Lesser max speed & more torque (than dc motor)
low speed, high precision applications
in dc motor, outer magnetic field is fixed, inner coil current direction varies
in stepper, outer is varied by giving 1 or 0, inner is fixed
Variable reluctance stepper

internal (rotor) is ferromagnetic (~iron) [others have permanent magnets]
outer (stator) coil pairs with one end fixed (Vcc), can GND (other end of) each coil pair one by one

Unipolar

rotor is a permanent magnet
stator coil pairs with joint (tap) in between. Can play with both ends.
center tap = Vcc, other ends = GND alternatively (direction)
full tapping sequence (1 ON at a time)
power tapping (2 ON at a time) - 1.4 times torque/power
half tapping (1 and then 2 ON alternatively) - more precision

Bipolar

stator without tapping
Each coil given Vcc at one end & GND at other end (alternatively)
need H-bridge for every coil pair
more difficult to control
better size to torque ratio

Universal stepper

4 independent windings (8 leads)
connect in series = bipolar
connect in parallel = unipolar

Driving stepper motors

Translator --> Driver --> Stator
For var reluctance/unipolar (common Vcc, other side GND), driver can be TTL buffer + power transistor + diodes to protect coil & transistor
ICs: ULN2003 (Transistor array), 7407 (buffer array), MC1414
For bipolar, h-bridge needed for each coil to reverse polarity
CMOS 4027 dual JK flip-flop IC with CMOS 4070 XOR logic for direction - working not clear
Adding 2 XORs based circuit to prevent h-bridge from getting both inputs high - not clear
Complete diagram 555+74194+buffers+transistors+motor +diodes - page 944
SAA1027 IC: driver + translator
uC acts as a software translator --> driver --> stator

Identifying stepper motors: using resistance between leads

Audio electronics

sound —> electric signal (mike), electric signal to sound (speaker)
frequency, intensity (loudness / energy), timbre (overtones / harmonic spectrum)
human ear can hear

frequency: 20-20,000 Hz, 1-2 KHz most sensitive
intensity: 10^-12-1W/m^2 (0-120 dB). dB = 10*log(I/I0), log is to the base 10, I0=10^-12

harmonic spectrum (spectral plot)

nth harmonic freq = n * 1st harmonic freq (i.e., the fundamental freq)
intensity of each harmonic can vary depending on instrument / it’s construction
complex signal can be expressed in fourier series, each harmonic = a*sinwt + b*coswt (summation of harmonics)
it’s complex to replicate an instrument’s sound: all overtones and decay and rise times, there are special oscillator and modulator circuits

microphones

variation in sound pressure —> variation in electric current
dynamic

plastic diaphragm captures sound waves —> voice coil vibrates on magnet, generates electric current/voltage
rugged, doesn’t need external voltage
many applications

condenser

sound sensitive capcitor: one fixed plate (GND), one flexible (VCC)
crisp low noise sound

electret

charged plastic element placed in parallel with a conductive metal plate

characteristics

sensitivity - ratio of output (electric) & input (sound) intensity (in dB)
frequency response - ability to convert different sound frequencies into ac voltages
directivity - capture sound well from one direction or all
impedance - load Z should be > 10 * source Z. 50 ohm mic, 600 ohm mixer

Audio amplifiers

Op amp based: inverting, non-inverting
digital: class D. input signal & triangle wave —> comparator (pwm) —> high power switch (mosfet amplifier) —>low pass filter (LC) (amplified signal)
ICs: NCP2704, LX1720
reducing hum

due to power supply: add as much smoothing capacitance as possible
mutual induction in wires or tracks: keep pcb tracks as short as possible

Preamplifiers

circuits to control input (select), level, gain, Z
various circuits using op amp or transistor

Mixer circuits

simple summing of signals
POTs at beginning of each signal to control it’s intensity
circuits using op amp or transistor (why extra cap to ground AC signal - not clear)

Impedance matching

not needed in modern devices (transistor / op amp based)
bridging needed i.e., destination device i/p Z > 10 * source device o/p Z
if transmitted signal is current, source Z should be > load Z

Speakers

dynamic: electric signal —> (moves) coil on magnet —> (moves) paper cone (emits sound waves)
frequency response: woofers <200 Hz, midrange speakers 500-3000 Hz, tweeters > mid range
speakers having all these are better than full range ones (100-15KHz)
crossover networks:

circuits having filters to divert right frequency to right device
passive: using L/R/C, near speaker, eats power, cheap, easy2make, can be tailored
active: using op amp, before amp so eats less power, controls all frequencies (LF356 along with low/band pass/high filters using passive components)

ICs to drive speakers

LM386: low power apps, to drive 8 ohm speaker, gain 20 (can be raised to 200 using R-C)
LM383: power amp, to drive 4 ohm speaker, thermal shutdown, heat sink required

Audible signal devices

simple warning signal indicators
dc buzzer, compression washer, sonalert audible sound device

Miscellaneous audio circuits

Tone generator using UJT
Metronome

Modular electronics

Good list of ICs for various purposes

Audio including audio recording
Power control
LED drivers
Misc

List of useful modules

RF modules
Audio modules
Power control
Display modules
Sensor modules

Power distribution and home wiring

Error analysis

if measurements are added/subtracted, add errors
if measurements are multiplied/divided, add errors like errorX/X+errorY/Y
Complex formulae if measurements are independent (uncorrelated), errors follow gaussian (normal) distribution
Full formulae to calculate uncorrelated errors - page 982
avoid designing experiments where 2 large quantities are measured and their difference obtained

Book review (Dec 2020)

1. When designing for production all components are to be considered w.r.t environment (temperature, pressure, humidity, noise etc.) e.g. temperature coefficient of resistors

2. Current - coulombs, charge / s

3. Voltage - energy / coulomb (force on electrons)

4. Power - energy / s

5. Electrons can be moved by forces like

- chemical (batteries)

- magnetic

- light (photons)

- thermal (mV, mostly noise)

- piezoelectric (mV)

- static electric (noise)

6. Thinner wire has more resistance per unit length than thicker wire

>> choose thickest track width on PCB as long as board size/layout/cost are not significantly impacted

7. In conductors, when temperature increases, resistance increases

>> In semi-conductors, resistance decreases with temperature increase

8. In next project, measure and note all V, I, Power (used / lost in heating) in all lines. Update on paper schematic. Expected maximum vs actual

>> choose components with 2 or 3 times capacity & with lower temperature coefficient

9. Grounding electrostatic wrist strap / mat if using mosfet etc.

10. Analog (mic/speaker) and digital ground should be separate

11. If using R <=100 ohm, consider power rating (Since I will be high)

>> power rating should be 2/3 times max expected power

>> generally 1/4 W is ok

12. Resistor voltage divider: the 10% rule

>> bleeder current is 10% of load current, hence bleeder R is 1/10 load R

>> if multiple loads, bleeder I is 10% of total (sum of all) loads current

13. Since voltage (or I) sources are not ideal, check actual voltage across each component (with load connected

14. Transistor (or a pair of them) can be used as current source

15. Combining 2 sinusoidal waveforms

>> when waves of similar magnitude & freq are combined, we get a composite waveform. Visible in sound beat notes.

>> when waves of widely different magnitudes & freq (e.g. 1k & 10k Hz) are combined, it seems one wave (the higher freq one) is riding on another. Concept of modulated signals.

16. If you use capacitors in series to withstand larger voltages, it’s a good idea to also connect an equalizing resistor across each capacitor. Use resistors with about 100 ohm per volt of supply voltage, and be sure they have sufficient power-rating/handling capability

17. For high frequency circuits, consider the accurate models of R L C. C, L behaviour curves per frequency

18. Even if a charged capacitor is grounded, charge (Q=CV) remains on it - electric field acts like a glue

19. using capacitor to control storage and delivery of charge

>> using difference capacitances, you can hold different amount of charge (hence I) for a given potential difference

>> also can maintain different potential differences for a given charge (or I)

20. R: 2*V —> 2*I; I V in phase

C: 2*f —> 2*I; I leads V by 90*

I: 2*f —> I/2; I lags V by 90*

Phase angle in impedance (Z): -ive means net capacitive, +ive net inductive

Phase angle in current (I): +ive means net capacitive (I leads), -ive net inductive (I lags)

21. LC resonant

- series (becomes wire at f0), parallel (becomes open at f0)

- L & C impedance >> R, sharp response (high q, low BW)

- L & C impedance ~= R, broad response (low q, high BW)

- At high f, inductor resistance dominates quality

- line I, circulating I

- Parallel

- At f0, like an open switch (I—>0, Z high)

- move in either direction, closed switch (I high, Z—>0), half power -3dB point

- Series

- At f0, like a closed switch (I high, Z—>0),

- move in either direction, open switch (I—>0, Z high), half power -3dB point

- In parallel

- I min does not have to be at Xl=Xc
- if Q>10, assume above & can use f0 = 1/sqrt(LC)

- A series LC circuit without any resistance would oscillate forever without damping.

Shock absorbers on an automobile, for example, are part of a mechanical harmonic oscillator designed to be nearly critically damped

22. Transient circuits - forced + natural response

23. Batteries: primary (table 278), secondary (table 284), supercap

selecting the right battery (table 287)

capacity: mAH, 1C is 1 hour discharge i.e., xmAH/xmA, if you run at 0.5C, battery will run for 2 hrs

24. switches - page 292

- sparkfun article

- mechanical relays: high current (2-15 A), slower switching (10-100 ms)

- reed relays: moderate current (0.5-1A), moderately fast switching (0.2 to 2ms)

- solid-state relays: wide range of currents (few mA to 100A), fast switching (1-100ns)

25. There are many types and characteristics of resistors / capacitors / inductors - read chapter 3 again carefully while choosing for real

26. semiconductors photo pg 407

27. diodes table pg 411

28. battery backup - if main is off, battery can give power via diode (diode conducts only if other side is lower than battery’s)

29. diode types table - pg 428

30. transistors types summary - pg 430

Electronics

Tuesday, 30 June 2020

Book notes - practical electronics for inventors

Motors (23-25 nov)

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Book review (Dec 2020)