In fact, this 1967 Electronic Design circuit generates two symmetrical ramps whose frequency depends on the values of the components used. Modern equivalent transistors can be used.
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...