This 4-tube circuit was found on a Radio Craft from December 1945. The circuit has excellent sensitivity. Power comes from a power supply with a transformer.
This simple timer uses one of the six inverter ports on a CMOS integrated circuit. Rx and Cx...
This circuit can be used as a residential doorbell. We found it in an English publication from...
In the old original version of this circuit from 1989, the LED is common (we recommend 330-ohm...