This circuit has the intensity of the signals controlled by the light that falls on the sensor. Note that it is not a frequency-controlled oscillator. Equivalent transistors can be used.
Two tone siren (CB9085E) This circuit was found in a 1980’s Radio Electronics. The signal must be...
Found in an American publication from the 1980s, this circuit can be found in commercial sound...
We found this circuit in an 80's Radio Electronics. The circuit uses a PTC sensor and an LED...