We found this circuit in an English publication from the 1980s. The circuit uses current components and can be tuned for frequencies between 300 and 1500 Hz.
This small transmitter with 2 transistors can reach several hundred meters using a 30 to 70 cm...
This circuit was found in a Modern Electronics from 1990. It activates an old electromechanical pulse counter,...
Although the integrated used originally is uncommon today, more modern operating equivalents can...