Introduction

Hello and welcome to 4QDtec.com This site contains a wide range of circuits and general electronic design information created by the founder of 4QD. It started life as a subscription club, but has now evolved into a free access site. It was written a while ago without the style tools that available now, so apologies for the way it looks, but hopefully you'll find the content useful. A lot of the circuits are designed using discrete components rather than ICs, this was the author's personal preference and can provide a solid, old school grounding in fundamental electronic design principles.

Copyright

4QD Ltd manufacture electronic motor speed controls for battery motors. We don't publish our latest and commercially sensitive circuits. However a lot of the ones here are original and although you are free to use them for your own entertainment, 4QD Ltd retains intellectual property rights to them insofar as they may have commercial value. If you do find them commercially useful, then please contact us for permission to use them. Under no circumstances may they be published in any form without written permission from the author.

Disclaimer

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. 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.

Site Index

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.

The index is one long list of all available circuits in alphabetical order. It is however divided into the following areas:

Index Contents

Audio Circuits

Automobile Circuits

Battery Monitoring circuits

Beginner's articles

Circuit Theory and tutorials

Component types and values

Components

Computing

Current sensing and control

Guitar Effects Circuits

LED Control circuits

Industrial Control circuits and suggestions

Measurement Circuits

Motor Control Circuits

Multivibrators

Oscillator Circuits

Power Supply circuits

Pulse (Width and position) Modulation Circuits

Relay Driver Circuits

Staircase generators

Switch Circuits

Test Equipment circuits

Temperature Measurement

Timer Circuits

Ultrasonic Circuits

Voltage/Current controlled circuits

Alphabetical Index

Analogue circuits, Various (Download zip file)

Analogue 'counter'

Analogue difference detector

Analogue isolator

Astable Multivibrators

Audio Circuits

Amplifier, very low THD

Sinclair circuits and other Sinclair info

Graphic Equaliser

Preamplifiers

LED VU meter

LED VU meter

Peak program indicator, speaker powered

Various Audio circuits (Download zip file)

Automobile Circuits

Various Auto circuits

Automotive Trafficator Circuit

Tacho and Dwell Meter

Battery Monitoring circuits

Battery Condition Meters the circuits of 4QD's own BCM.

Battery discharger

Battery low indicator

Various Battery circuits

Beginner's articles - A selection of articles written for those new to electronics

Electricity - an analogy with water

How pwm works

Bistable Latch

Bridge, Full. For motor control

Bridge, Full. Switching of

Bridge, Half. For motor control

Bridge, Half. Current and voltage commutation waveforms

Charge pump. Cup and bucket

Circuit Theory and tutorials

Colour codes and multipliers for resistors and capacitors

Current sources and mirrors

Electricity - an analogy with water (good start for beginners)

Emitter Coupled Multivibrators

Filter Circuits (Download zip file) Single transistor Gyrator, Multi-feedback, Twin T

Logic circuits using discretes

Mice How your computer mouse works

Op-amp circuits using discrete transistors

Two transistor regulator circuits

Various Circuit Configurations (Download zip file)

Components

Reed switches How to use them

Component types and values

Colour codes and multipliers for resistors and capacitors

Testing MOSFETs

Comparator with controlled hysteresis

Component values and colour code

Converter circuits (Download zip file) D to A, V to Time

Cup and bucket charge pump

Computing

Possible bug in Wireless Router adaptive learning?

Current sensing and control

Current Controlled Amplifier

Current loop interface

Current Monitoring Circuits

Current sensing relay driver

Current sources and mirrors a 'lecture'

Current source, Switching

Data switch and indicator, bi-directional

Discrete transistor Circuits (Download zip file) Op Amps, Logic

Driver Circuits Totempole drivers

Domestic heating control circuit

Electric Field detector

Electricity - an analogy with water (good start for beginners)

Follower Circuits

Full bridge for motor control

Game circuits

Graphic Equaliser

Guitar Effects Circuits

Phaser

Gyrator - used in graphic equaliser

H Bridge Switch. For small motors

Hall effect Current sensing

'Jeopardy' circuit

Industrial Control circuits and suggestions

Analogue 'counter'

Analogue isolator

Bistable Latch

Coil catching diodes AKA flywheel diodes. Why they are needed.

Current loop interface

Current sensing relay driver

H Bridge Switch. For small motors

Industrial process control circuits

Impulse relay circuit Pulse to set, pulse to reset

Modular industrial relay system Base relay allows timers etc to be added

Opto isolator, Analogue

Relay driver, transistorised

Stepper motor, clock oscillator

Switch, Impulse changeover

Switching Solenoid Driver

Timer circuits

Impulse changeover Switch

Industrial process control circuits

Intercom with speaker as microphone

Joystick Interfaces

Lab Power supply (Download zip file) 0-50 volts, 0-5 amps or whatever you decide.

Lamp and Bulb drivers

Latch, Data bi-directional

Leakage detector

LED Control circuits

LED Driver Circuits

LED Volt Meters 4QD's 3, 5 and 7 LED voltmeters, circuits, partslist, descriptions

LED VU meter

LED brightness control circuits

Logic circuits using discretes

Logic Circuits (Download zip file) Latches. Transparent data, R-S etc.

Mains Wiring detector

Mathematical Analyses (Download zip file) One TUN gyrator

Mice How your computer mouse works

Microphone preamplifiers

Modulators, Pulse Width

MOSFET current sensing

MOSFET testing

Measurement Circuits

Hall effect Current sensing

LED Volt Meters 4QD's 3, 5 and 7 LED voltmeters, circuits, partslist, descriptions

LED VU meter

Testing MOSFETs Use a multimeter to test a MOSFET

Peak Detecting Circuits

Motor Control Circuits

Analogue isolator

Battery Current Limiting

Bridge, Full. For motor control