Found in a 1968 EEE, this circuit accepts frequencies from 1 to 1000 Hz and control voltages from 0.1 to 15 V. The operational amplifier is from the era and can be replaced by modern equivalents.
This circuit was obtained from an American publication from the 80's. We can use a BD136 instead...
This oscillator for the practice of telegraphy provides a good sound in a loudspeaker, with only...
This simple circuit to monitor the frequency of the power grid uses an analog indicator. The...