This circuit is from a 1969 EEE magazine. The transistors are from that time, but the circuit can be implemented with modern equivalents, such as 2N2646 for Q3.
We found this circuit in Radio Electronics Special Projects from 1992. The circuit turns on the...
We found this circuit in the Texas Instruments' Linear Circuits Applications. It uses an...
This capacitive sensor that operates with a high frequency oscillator was found in Radio...