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.
This circuit is from a 1995 publication; The current is obtained by dividing 1.25 by R1. The...
We found this circuit in an old American publication. It is possible to test common FETs using a...
This circuit was obtained in a 90s documentation from Analog Devices. The sensitivity is in the...