This circuit was found in the September 1971 Radio Electronics magazine. The buzzer can be replaced by a relay according to the supply voltage. R1 adjusts the sensitivity.
This circuit converts BCD inputs to analog voltages. The operational amplifier must be powered...
This circuit is suitable for the calibration of old analog oscilloscopes. It was found in...
This is the circuit of a hearing aid amplifier manufactured by Sony in the 1960s. The circuit was...