This simple NAND gate timer circuit enables you to turn off a selected device after about 1 to 60 minutes. The circuit can be used to turn off gadgets such as radio, tv set, fan, pump etc after a predefined time of 60 minutes. Such a circuit can easily gain a lot of electricity.
The proposed timer circuit is dependent on quad 2 input CMOS IC 4011 (U1). Resistor R1 and capacitor C1 create the long time required. Once push-button S2 is depressed, capacitor C1 discharges and the input of the four NAND gates is pulled to zero. The four short-circuit outputs of U1 become high and activate transistor Q1 to drive the relay. The gadget associated through the use of the relay is switched on. Whenever S2 is released from the C1 starts charging and if the voltage at its positive pin becomes equal to half the supply voltage at the outputs of the U1 becomes zero and the transistor is turned off. This causes the relay to be deactivated and the connected device via the relay is deactivated.
The discussed 1 to 60 minute timer can be made to stop if necessary by pushing switch S1.
