We found this circuit in a 90s Radio Electronics. The circuit generates frequency-modulated 220 kHz signals. The components used are still common.
The frequency of the sound emitted by this circuit depends on the light intensity on the sensor....
This circuit is based entirely on SCRs. The circuit is from an American 80's documentation; and the PUTs...
This circuit was found in a 1980s instrumentation publication and can be applied to virtually any...