This circuit is from a Hands-On Electronics from the 90s. The integrated amplifiers used are well known. The range is a few tens of meters depending on the resistance of the cables.
Luminus SST 20 Deep Red LED Mouser Electronics is announcing in its stock the SST-20, a 60%...
This 4093 IC continuity tester was found in the November 1986 Radio Electronics magazine. The...
This receiver circuit was found in a Hands On Electronics from the 90s. The circuit uses a PLL...