Found in old documentation, this source uses an integrated circuit from that time, which is uncommon nowadays. The power source has a ripple below 1 mV.
The frequency of the sound emitted by this circuit depends on the light intensity on the sensor....
This circuit is from a thyristor manual from On Semiconductor. It makes use of a PUT and a SCR...
This circuit uses only one NC75Z04 port from ON Semiconductor, but it can be implemented with...