This circuit is from a Popular Electronics from the 90s. It uses an opto-coupler with SCR directly controlling a 20 mA current load.
This interesting circuit found in American documentation generates a busy signal, without you...
In this circuit R1 is 56 ohm and R2 is 220 ohm for the 110 V network. SCRs are according to the...
We found this circuit in a 70s EDN. The circuit makes use of operational of the time. | Clique na...