We found this circuit in a 73, magazine for radio amateurs of the 90s. The circuit is passive and most telecommunications receivers can be added.
This circuit, found in a 1986 documentation, uses an optical sensor to count pulses and, in its...
This circuit, found in a 1997 publication, activates a lamp or a monitoring camera when the bell...
We found this circuit in an English publication in 1981. It can be improved by exchanging T1 for a...