Audible Voltmeter (CB21395E)

This circuit was found in an American publication from 1969. Transistors are from the time and can be replaced by modern equivalents.

| Clique na imagem para ampliar |

Varicap Spy Transmitter (CB19433E)
This circuit with variable capacitance diode (varicap) is from a publication from the 90s. The...
Divider by N with the 4017 (2) (CB12131E)
With this circuit it is possible to divide the frequency of a rectangular signal by values between 2...
Triac driver (CB22446E)
The presented circuit uses an optocoupler to trigger a triac. We found it in a Popular Electronics from...