This simple optical alarm circuit was found in the 1991 Electronics Experimenter Handbook. The circuit uses a lamp as the emitter but can use LEDs.
The circuit presented is quite simple, employing tone modulation of the signal. To receive the...
Operating in the FM range, this is one of the many versions of FM transmitter that the reader can...
This sensitive photo-relay can be mounted with modern transistors such as BC558 and with the...