It is not easy to design an oscillation circuit using a transistor. This is the simplest oscillator for beginners. It uses a Vbe breakdown phenomenon to reset the CR charged electricity. The C, in this case, is a Piezo sounder. It usually has 3-30nF capacitance at audio frequency. It is charged till the breakdown voltage (about 8V), and is reset to about 5V. It starts charging again, resets, and so on. As a result, the Piezo buzzes according to the CR time-constant. Try a variable resistor or a Cds cell for R..
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The breakdown in transistor, is the phenomenon to be avoided in practical design. It is reported that it damages the transistor characteristics (i.e. a lowering of hfe). Use UJT or PUT (Programmable Uni-junction Transistor), instead.
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I arranged this piece for an anode common color LED. Each LED blinks by C charged electricity, and consumes less power.
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12 Aug. 2010
6 Oct. 2010 - Color LED added.
Osamu Tamura
