We found this circuit in a 1977 factory documentation. The operational amplifiers can be 741 and the symmetrical power supply. Capacitors can be changed for operation at other frequencies.
In the circuit of the figure, when pressing S1 the sound varies according to the value of R2 and...
May 2017 - The new ROHM SFR series anti-sulfur resistors can now be obtained from Mouser...
Suggested by General Electric documentation from 1968, this circuit activates a relay after 60...