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.
Of course, the current is extremely small, but a voltage of 300 V can be obtained from 9 V of a...
This battery monitor circuit with the TLV379 low voltage operational amplifier was obtained in the...
This circuit can be connected to the output of alarms or sirens with the 555, CMOS or TTL,...