We found this circuit in the November 1992 Radio Electronics magazine. The circuit uses an LDR as a sensor and the transistor can be any general-purpose transistor.
This circuit converts infrared pulses into audio and can be used in an experimental telegraphic...
This circuit was found in an old Poptronics but is still current as transistors can be replaced...
The search coil of this detector consists of 140 turns of wire 18 in an 8 inch diameter form. The...