This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time and the frequency is determined by the crystal. The circuit operates at voltages from 3 to 9 V.
This alarm, found in a 2002 documentation, uses several sensors and has a 12 V supply, not...
This circuit was found in a 90's EDN. The circuit provides two 15 V outputs and one 5 V output...
This circuit generates 5 different tones selectable by switch S1. Separate pressure switches can...