This simple injector circuit can actually be powered by voltages from 3 to 9 V. The frequency is given by C1 which can be between 4.7 and 10 nF. The CMOS can also be 4011.
This additional bell circuit was found in the February 1994 Electronics Now magazine. The...
A delay of a few seconds to a few tens of seconds can be achieved with this circuit found in a...
This circuit uses a transistor to trigger the alarm from a low quiescent current sensor. The relay...