Newest circuit diagrams

Metal Detector

A single chip metal detecor with a range of a few inches. This is useful for decting nails or screws in walls and floors, or for locating buried mains cable.

ECM Mic Preamplifier

A microphone amplifier that may be used with either Electret Condenser Microphone (ECM) inserts or dynamic inserts, made with discrete components.

Variable PSU 3-15v

A variable power supply with adjustable voltage and current outputs made with the L200 regulator.

Variable Power Supply Using Fixed Regulator

This is a similar power supply that I used to power my FM Transmitter. After suffering long problems with mains hum, this design using a pi filtered C-L-C approach. This circuit offers excellent ripple rejection.

Hot Water Level Indicator

A simple device to indicate various levels of hot water in a tank.

Water-level Alert

Beeper or flashing LED alert 1.5V battery powered portable unit

Dark-activated LED or Lamp Flasher

Simple photo-sensitive circuit. 3V battery supply

Bug Detector

This circuit can be used to "sweep" an area or room and will indicate if a surveillance device is operative. The problem in making a suitable detector is to get its sensitivity just right; too much and it will respond to radio broadcasts, too little sensitivity and nothing will be heard.

Fridge door Alarm

Beeps if you leave open the door over 20 seconds 3V battery operation, simple circuitry

Quiz Circuit

I've had a few requests for a quiz circuit, so here is a 4 input design which can easily be modified.