Phone circuit (CB8709E)

With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a basic intercom.

Diac Light Pulse Generator (CB14687E)
We found this relaxation circuit with diac in an opto-electronic documentation with diac....
Dark activated alarm with hysteresis (CB7868E)
Found in American documentation from the 90s, this circuit can be implemented with modern...
SCR Trigger Circuit (CB16413E)
In the figure we have a very simple trigger circuit for an SCR that powers a 12 V lamp whose...