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 shown, found in a 2004 documentation, allows the use of a telephone, without the...
This simple circuit needs a high gain stage to compensate for losses. It consists of a passive tone...
The time constant for this circuit found in a 1973 publication is given by R and C. The shot is...