This circuit can activate a powerful lamp or call system when a telephone call occurs. Suitable for hearing impaired or noisy places it was found in American documentation in the 90s.
The basis of this circuit is a CA3130 operational amplifier. The transistor can be BC548, and the...
This circuit, found in a 73 magazine for radio amateurs, is used in radio localization. The...
This circuit is from an American magazine Popular Electronics of March 1991. The circuit produces both...