Gold Detector Schematic

Here the very simple and easy build gold detector circuit. The circuit capable to sense gold or metal or coins from a distance of about 20cm, depending on the size of the object to detect.

The circuit oscillates at about 140kHz and a harmonic of this frequency is detected by an AM radio. You can simply tune the radio receiver until a squeal is detected.

Simple Intercom Circuit with Transistors

This is a 2-station simple intercom circuit build based on transistors part and using common 8R mini speakers. The speaker works as microphone and generate sound, so there is no need microphone for this intercom. The "press-to-talk" switches should have a spring-return so the intercom can never be left ON, push on switch can be used for this kind of task.

Interior Light Fader for Automobile

Here the circuit diagram of Interior Light Fader for Automobile. The circuit is build using low power operational amplifier LM324 which only need around 3mA of current, so it won't bother the battery supply if left connected for extended periods. This circuit is similar to the fading eyes circuit above and is used to slowly brighten and fade interior lights of older cars.