This is may be the simplest radio transmitter that you will find anywhere. lt has a total of fiye parts and can be constructed into a very small space. It is great for science fair projects or other science related projects where short range transmission is useful.
lt runs on 1.5 to 3 yolts, with small hearing aid batteries or lithium “coin” cells being ideal. A thermistor or photoresistor can be inserted in series with R1 to have a varying output freguency dependent on the input. The frequency can also be changed by changing the yalue of C1. A 2N2222 transistor is recommended, but you can try other types also.
Performance tends to vary from type to type as well as from transistor to transistor. L1 is 20 to 30 turns of thin magnet wire (24 to 32 ga.) close wound around a 11S to 1.·’4″ diameter non-conductiye form. The coil is tapped 1:3 of the way from one end and the tap connected to the emitter of Q1. Experiment with all of the yalues in this circuit. Nothing is critical, but performance can be yaried considerably.
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