This circuit that can be activated by light or heat was found in an old American documentation, but the components it uses are perfectly current. The power transistor shall be fitted with a heat sink.
Using a 4046 PLL this circuit recognizes a 1.6 to 1.8 kHz tone by driving an output LED. The...
The frequency of this oscillator depends on the crystal used and the transistors. The circuit was...
This circuit is from the American magazine that no longer exists Science & Electronics,...