This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference, as this type of dialing is no longer used today.
We found this circuit in an old American publication. The transistors can be BC558 and diode 1N34....
This simple circuit operates with only 1.5 volts of a battery and detects low resistance making a...
The cascade connection of two flip-flops allows division by 4, as shown in the figure. Note that...