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There are not many AM transmitters that are easier to build than this one because the inductor is not tapped and has a single winding. There is no need to wind the inductor as it is a readily available RF choke (eg, Jaycar Cat LF-1536). To make the circuit as small as possible, the conventional tuning capacitor has been dispensed with and fixed 220pF capacitors used instead. To tune it to a particular frequency, reduce one or both of the 220pF capacitors to raise the frequency or add capacitance in parallel to lower the frequency. Q1 is biased with a 1MO resistor to give a high input impedance and this allows the use of a crystal ear piece as a low cost microphone.... [read more]

If the unit is brought close to a live conductor (insulated, and even buried in plaster) capacitive coupling between the live conductor and the probe clocks the counter, and causes the LED to flash 5 times per second, because the 4017 IC divides the mains 50Hz frequency by 10.... [read more]

There is little to be said about this circuit. All the work is done by the regulator. The 7809 can deliver up to 2 amps continuous output whilst maintaining a low noise and very well regulated supply. The circuit will work without the extra components, but for reverse polarity protection a 1N5400 diode (D1) is provided at the input, extra smoothing being provided by C1. The output stage includes C2 for extra filtering, if powering a logic circuit than a 100nF (C3) capacitor is also desirable to remove any high frequency switching noise.... [read more]

This is a simple use of the PIC 16F84 about a diode tester.... [read more]

Every self-respecting DIYer makes his own electronic dice with LEDs as spots. Then you don’t have to throw the dice anymore – just push the button. The electronics also ensures that nobody can try to improve his luck by fiddling with the dice. Too bad for sore losers! This circuit proves that an electronic die built using standard components can be made quite compact. The key component of here is a type 4060 digital counter (IC1).... [read more]

This circuit, connected with 32 Ohms impedance mini-earphones, can detect very remote sounds. Useful for theatre, cinema and lecture goers: every word will be clearly heard.... [read more]