This is one of the first radios with an integrated circuit. The circuit is from a Radio Electronics from November 1969. The circuit is powered by a 9 V battery.
In the figure we have a receiver for frequency modulated light signals (see the transmitter in...
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
This circuit has an improvement over the previous one as it also has an LED indicator for correct...