This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
This circuit was suggested in a 1976 documentation. We can use the pair BD135 and BD136 on the...
The original application of this 1967 Ferranti circuit can be changed so that it functions as a pass...
This source whose voltage depends only on the zener diode used, can supply currents up to about 3 A....