This circuit was found in a 90s Popular Electronics. It is used for the acoustic transmitters of 40 kHz, as several found in this section. Transistors support current equivalents.
This alarm goes off if someone leaves a door open. We found it in the Encyclopedia of Electronic...
The pulse duration is determined by the 100k resistor and the separation by the 1M resistor. The...
This circuit uses high voltage transistors to provide direct power from the 110 V power grid or a...