This interesting circuit uses a sodion valve that we have already described in an article on the website. The circuit uses several batteries for power. The phone is of high impedance.
This shield circuit is suggested by Texas Instruments and can employ almost any optical coupler...
In the figure we have a monostable that is activated with switch S1 and pressed for an instant. The...
This circuit for alternating current was found in a 1965 General Electric documentation. The...