Time relay do it yourself transistor and relay
It is shown how to make a time relay with your own hands from a transistor and an electromagnetic relay. The operating time of the relay sets the RC circuit, consisting of a resistor and a capacitor. Considered the scheme of the time relay works as follows. The capacitor is charged first, and then the capacitor discharges through a resistor. The discharge current of the capacitor leads to the opening of the transistor, which in turn supplies power to the relay coil. Further, after the relay is triggered, a blocking contact is opened or closed, and accordingly, the load is switched on or off.
The operating time of the relay is determined by the parameters of the RC circuit and the resistance of the pn junction base-emitter of a bipolar transistor.