This simple bridge circuit can be used for impedance or resistance measurement using a high impedance earphone as an indicator. The circuit is from an American 80's documentation.
In the figure we show how to use a varicap to modulate a signal in frequency. The circuit can be...
The astable multivibrator shown by figura 1 has a very low current drain and can be powered from 6...
This circuit is from an 80's component manual. However, the circuit may be of a modern equivalent...