Variometer for radio (CB21212E)

This antenna tuning circuit was found in a Popular Electronics from the 90's. The coils depend on the tuned frequency ranges.

DC to DC Converter (CB6580E)
This circuit was found in an American documentation from 1970. We can increase the number of...
Automatic Faucet (CB18147E)
The presented circuit allows to control the valve of a tap. The positioning of the emitter and the...
Operational Amplifier Test (CB11246E)
I found this circuit in an old British magazine from 1976. It is possible to test operational...