This page contains the main index to the electronics section of this site, with certain other general information which you may need.
This site, large though it is, is only the public 'front end' of a subscription electronics club - 4QD-TEC.
For more information and how to join, use the 'Join' button at head or foot of any free page.
As these pages of circuits (a lot more at the bottom of this one) are proving to be of interest to browsers we are gradually expanding them to give a larger selection of interesting and, perhaps, useful circuits as well as a lot of various information. We want to make our site interesting and useful - not pretty and impressive. Hopefully some of you, one day, may need a PWM motor controller and will remember us!
I know a lot of visitors are coming straight to this index rather than to our Home page. You are welcome - but there are pointers on the home page to other info which is not circuit diagrams. There will be links to other sites, info on manufacturers and suppliers of goods related to our business as well as information on computing and electronics and maybe other subjects. Who knows what else! The author has written for computer magazines, DIY magazines and others.
4QD sell motor controllers: we do not sell web technology. Therefore you won't find animated GIFs, Java Applets or advice to use one particular browser: our pages should work with any browser that can display GIFs and JPEGs. There will be added, in time, one or two JavaScript calculators however.
All of which the above makes this site a very good educational resource, and it is evident from the comments we get that it is being used as such. So we intend to expand this area - partially in an attempt to make the site commercially viable. We intend therefore to make circuit board designs available for some of the projects and educational establishments that require reasonable quantities (25 or more) are welcome to contact 4QD to discuss their requirements. We will be able to supply circuit boards for some of the interesting circuits, with kits of parts and assembly information. We can clearly link the boards and kits to constructional information on this site, or we can supply printed out information.
I have however tried to make this site easy to read, so the descriptions aren't too simple or full of maths. Maybe you want this altered - let me know.
The public area of 4QD-TEC is large: future expansion will be in the private area, which is only available to members. This data includes much on PWM motor control (as you might expect) but also lots of other information, including more detailed circuit descriptions and constructional information.
4QD manufacture electronic motor speed controls for battery motors. We make our living by selling some of our circuits. Obviously I'm not going to publish commercially sensitive circuits! However a lot of the ones I publish are original and although you are free to use them for your own entertainment, the author retains intellectual property rights to them insofar as they may have commercial value. If you do find them commercially useful, then please contact me for permission to use them. Under no circumstances may they be published in any form without written permission from the author.
These circuits are supplied 'as is' at no charge, for your enjoyment. So far as we are aware they are complete and work but we can take no responsibility for any errors. We will of course offer any reasonable assistance if you do hit problems. Most, but not all, of the circuits are our own design. As far as we are aware no copyright other that the author's exists on any of them but we cannot guarantee this.
The list below is not as long as it looks because it sometimes contains many entries to the same circuit. If so, this is because the circuit has many uses or can be called different things (besides - it makes the list longer!)
Some of these items are public. Some are members only. Some have a public 'front' but more is available to members. So the left hand column is a key to what is what.
The index is one long list of all available circuits in alphabetical order. It is however divided into the following areas:
 | | | |
| ML | Analogue circuits, Various |
| PA | Analogue 'counter' |
| PA | Analogue isolator |
| PA | Astable Multivibrators |
| Audio Circuits |
|---|
| PA | | Amplifier, very low THD |
| MO | | Sinclair circuits and other Sinclair info |
| PA | | Graphic Equaliser |
| PA | | Preamplifiers |
| PA | | LED VU meter |
| PA | | Signal Generator |
| ML | | Various Audio circuits |
| Automobile Circuits |
|---|
| ML | | Various Auto circuits |
| PA | | Automotive Trafficator Circuit |
| PA | | Tacho and Dwell Meter |
| Battery Monitoring circuits |
|---|
| MO | | Battery Condition Meters | the circuits of 4QD's own BCM. |
| PA | | Battery discharger |
| PA | | Battery low indicator |
| ML | | Various Battery circuits |
| Beginner's articles | A selection of articles written for those new to electronics |
|---|
| PA | | Electricity - an analogy with water | |
| PA | | How pwm works | |
| MA | Bistable Latch |
| PA | Bridge, Full. For motor control |
| MO | Bridge, Full. Switching of |
| SM | Bridge, Half. For motor control |
| MO | Bridge, Half. | Current and voltage commutation waveforms |
| PA | Charge pump. Cup and bucket |
| Circuit Theory and tutorials |
|---|
| PA | | Colour codes and multipliers | for resistors and capacitors |
| PA | | Current sources and mirrors |
| PA | | Electricity - an analogy with water | (good start for beginners) |
| MO | | Emitter Coupled Multivibrators |
| ML | | Filter Circuits | Single transistor Gyrator, Multi-feedback, Twin T |
| PA | | Logic circuits using discretes |
| PA | | Mice | How your computer mouse works |
| PA | | Op-amp circuits | using discrete transistors |
| PA | | Two transistor regulator circuits |
| ML | | Various Circuit Configurations |
| Components |
|---|
| PA | | Reed switches | How to use them |
| Component types and values |
|---|
| PA | | Colour codes and multipliers | for resistors and capacitors |
| PA | | Testing MOSFETs |
| PA | Comparator with controlled hysteresis |
| PA | Component values and colour code |
| ML | Converter circuits | D to A, V to Time |
| PA | Cup and bucket charge pump |
| Computing |
|---|
| PA | | Possible bug in Wireless Router adaptive learning? |
| Current sensing and control |
|---|
| PA | | Current Controlled Amplifier |
| PA | | Current loop interface |
| ML | | Current Monitoring Circuits |
| PA | | Current sensing relay driver |
| PA | | Current sources and mirrors | a 'lecture' |
| PA | | Current source, Switching |
| PA | Data switch and indicator, bi-directional |
| ML | Discrete transistor Circuits | Op Amps, Logic |
| ML | Driver Circuits | Totempole drivers |
| PA | Domestic heating control circuit |
| PA | Electric Field detector |
| PA | Electricity - an analogy with water | (good start for beginners) |
| ML | Follower Circuits |
| PA | Full bridge for motor control |
| PA | Game circuits |
| PA | Graphic Equaliser |
| Guitar Effects Circuits |
|---|
| PA | | Phaser |
| PA | Gyrator - used in graphic equaliser |
| PA | H Bridge Switch. For small motors |
| PM | Hall effect Current sensing |
| PA | 'Jeopardy' circuit |
| Industrial Control circuits and suggestions |
|---|
| PA | | Analogue 'counter' |
| PA | | Analogue isolator |
| PM | | Bistable Latch |
| PA | | Coil catching diodes | AKA flywheel diodes. Why they are needed. |
| PA | | Current loop interface |
| PA | | Current sensing relay driver |
| PA | | H Bridge Switch. For small motors |
| PM | | Industrial process control circuits |
| PA | | Impulse relay circuit | Pulse to set, pulse to reset |
| PM | | Modular industrial relay system | Base relay allows timers etc to be added |
| PA | | Opto isolator, Analogue |
| PM | | Relay driver, transistorised |
| PA | | Stepper motor, clock oscillator |
| PA | | Switch, Impulse changeover |
| PA | | Switching Solenoid Driver |
| PM | | Timer circuits |
| PA | Impulse changeover Switch |
| PM | Industrial process control circuits |
| PA | Intercom with speaker as microphone |
| PA | Joystick Interfaces |
| MO | Lab Power supply | 0-50 volts, 0-5 amps or whatever you decide. |
| ML | Lamp and Bulb drivers |
| PA | Latch, Data bi-directional |
| PA | Leakage detector |
| LED Control circuits |
|---|
| ML | | LED Driver Circuits |
| MO | | LED Volt Meters | 4QD's 3, 5 and 7 LED voltmeters, circuits, partslist, descriptions |
| PA | | LED VU meter |
| PA | | LED brightness control circuits
|
| PA | Logic circuits using discretes |
| ML | Logic Circuits | Latches. Transparent data, R-S etc. |
| PA | Mains Wiring detector |
| ML | Mathematical Analyses | One TUN gyrator |
| PA | Mice | How your computer mouse works |
| PA | Microphone preamplifiers |
| PA | Modulators, Pulse Width |
| PM | MOSFET current sensing |
| PA | MOSFET testing |
| Measurement Circuits |
|---|
| PM | | Hall effect Current sensing |
| MO | | LED Volt Meters | 4QD's 3, 5 and 7 LED voltmeters, circuits, partslist, descriptions |
| PA | | LED VU meter |
| PA | | Testing MOSFETs | Use a multimeter to test a MOSFET |
| ML | | Peak Detecting Circuits |
| MO | | Voltage breakdown tester | for transistors and diodes etc |
| Motor Control Circuits |
|---|
| PA | | Analogue isolator |
| PM | | Battery Current Limiting |
| PA | | Bridge, Full. For motor control |
| PA | Part 1 | Bridge, Half. For motor control | A discussion |
| MO | Part 2 | PWM motor speed control | Deals with early 2QD circuits |
| MO | Part 3 | PWM motor speed control | Development of 2QD series |
| MO | Part 4 | PWM motor speed control | Modern 2QD series. Detailed discussion |
| MO | Part 5 | PWM motor speed control | Ramping and reversing. NCC series controllers |
| MO | Part 6 | PWM motor speed control | Waveforms and commutation in a MOSFET half bridge |
| MO | Part 7 | PWM motor speed control | MOSFET full bridge switching using two half bridges |
| MO | Part 8 | PWM motor speed control | MOSFET full bridge switching - Fully complementary |
| MO | | PWM motor speed control Part 7 | Starts to deal with Full bridge control |
| PM | | Constant Power throttle | How do simply incorporate constant power throttle |
| PA | | H Bridge Switch. | For small motors |
| PM | | MOSFET current sensing |
| PA | | Pulse Width modulators |
| ML | | Pulse Width modulators | Several circuits |
| PM | | A new PW Modulator | double triangle waveforms, independently adjutable slopes |
| PM | | PWM motor control | Many more articles, including constructional information and theory. |
| PA | | Tacho generator amplifier | As used in 4QD's Tacho feedback board |
| PA | Multipliers | (3n3 etc) for resistors and capacitors |
| Multivibrators |
|---|
| PA | | Multivibrators |
| MO | | Multivibrator, emitter coupled | Linear ramps, good waveform |
|
| MO | | Test ramp generator, for power device testing | A practical application of the emitter coupled multivibrator |
|
| ML | | Multivibrator circuits | Astables. Bistables, Ring Astables |
| PA | Op-amp circuits using discrete transistors |
| PA | Opto isolator, Analogue |
| Oscillator Circuits |
|---|
| MO | | Multivibrator, emitter coupled | Linear ramps, good waveform |
|
| PA | | Quadrature (sine/cosine) | voltage controlled, quasi-sinusoids |
| PA | | Three phase |
| PA | | Voltage controlled | programmable, wide range. |
| PA | | Relaxation oscillators | multivibrators |
| PA | | Wien Bridge |
| ML | | Oscillators | Multivibs, Ramp generators, Sawtooth,
Sinewave, Sounders, VCOs, Waveform Generators |
| ML | Peak Detecting Circuits |
| PA | Person detector |
| PA | Phaser for audio/guitar effects |
| Power Supply circuits |
|---|
| PM | | Power supplies with enable | and automatic switchoff |
| PA | | Power supply | tripped, regulated, high current |
| MO | | Power supply | Re-entrant, regulated, high Current |
| MO | | Power supply, Lab type | 0-50 volts, 0-5 amps or whatever you decide. |
| ML | | Power Supply Circuits | Various |
| PA | | Two transistor regulator circuits | a theoretical discussion |
| PA | Preamplifiers, audio |
| PA | Preamplifiers, ultrasonic |
| PA | Programmable Unijunction Transistor |
| PA | Precision rectifier circuit | in tacho amplifier |
| PA | Precision rectifier circuit | in Joystick interface |
| Pulse (Width and position) Modulation Circuits |
|---|
| PA | | Pulse Width modulators |
| ML | | Pulse Width Modulators |
| PA | | Pulse Width Position Servo control |
| PA | | PWM motor control - part one of a series | links to much more in member's area |
| MO | | 2QD controller | Circuit diagram, component list, PCB layout |
| ML | Pulse Processing Circuits |
| PA | Pulse width comparator |
| PA | Pulse width to voltage converter |
| PA | Pump and hold (staircase) |
| PA | PUT pair | 2 Tr equivalent to SCRs, SCSs and other 4 layer devices |
| PA | PWM motor control |
| PA | Quadrature (sine/cosine) oscillator | voltage controlled |
| PA | Radio Control Interface |
| PA | Ramp generator | (separate + & - ramps) |
| ML | Ramp Circuits | Ramping and Slew Rate control |
| PA | Relaxation oscillators |
| Relay Driver Circuits |
|---|
| PA | | Impulse relay circuit | Pulse to set, pulse to reset |
| PM | | Latching, transistorised |
| PM | | Relay driver, transistorised |
| PA | | Switching Solenoid Driver |
| ML | | Relay Driver Circuits |
| PA | Resistor colour code |
| ML | Rotary Encoder Circuits |
| PA | Robot wars: start here! |
| PA | Schmitt Trigger: an unusual circuit |
| PA | Sinewave Generator |
| Staircase generators |
|---|
| PA | | Staircase generator |
| PA | | Staircase generator |
| ML | | Staircase Generators |
| PA | Stepper motor used as encoder |
| PA | Stepper motor, clock oscillator |
| Switch Circuits |
|---|
| ML | | Toggle action switches |
| ML | | Data Switches |
| ML | | Touch operated Switches |
| PA | | Switch, Impulse changeover |
| PA | | Switch, Touch operated |
| PA | Switching Solenoid Driver |
| PA | Tacho generator feedback circuit |
| Test Equipment circuits |
|---|
| MO | | Lab Power supply | 0-50 volts, 0-5 amps or whatever you decide. |
| MO | | Voltage breakdown tester | for transistors and diodes etc |
| MO | | Test Ramp generator | For Power device curve tracing |
| ML | | Semiconductor Testers | JFET offset voltage tester, Diode Vf tester
Beta Meter, Bipolar polarity checker |
| Temperature Measurement |
|---|
| PA | | Thermometer and thermostat | for Room temperatures |
| PA | | Thermostat |
| ML | | Thermostat circuits |
| Timer Circuits |
|---|
| PM | | Timer: delay on de-energise |
| PM | | Timer: delay on energise |
| PM | | Timer: pulse output |
| PA | Touch operated Switches |
| PA | Twin-T oscillator |
| PA | Twin-T tuned Ultrasonic Preamp |
| Ultrasonic Circuits |
|---|
| PA | | Ultrasonic Intruder detector |
| PA | | Ultrasonic Preamp with AGC |
| PA | | Ultrasonic Preamp with Twin-T tuning |
| PA | | Ultrasonic Receiver |
| PA | | Ultrasonic Transmitter |
| PA | Understanding Electricity - an analogy with water |
| MO | LED Volt Meters | 4QD's 3, 5 and 7 LED voltmeters, circuits, partslist, descriptions |
| MO | Voltage breakdown tester for transistors |
| MO | Voltage breakdown tester circuits |
| Voltage/Current controlled circuits |
|---|
| PA | | Current Controlled Amplifier |
| PA | | Oscillator, Quadrature (sine/cosine) |
| PA | | Oscillator - multivibrator type |
| PA | | Oscillator, programmable, wide range |
| ML | | Voltage and Current controlled amps |
| PA | VU LED meter |
| PA | Waveform generator circuits |
| PA | Wien Bridge oscillator |
| ML | Window Detectors |
