Tuesday, May 24, 2011

Long Delay Timer Using IC 4011 Nand Gates

This following circuit shows a Long Delay Timer Circuit Diagram. This circuit designed mainly to switch off a portable radio after some time:

A very long time constant is provided by R1 and C1. C1 discharges and the near zero voltage at its positive lead is applied to the high impedance inputs of the four gates of IC1 wired in parallel when P2 is momentarily closed. The battery voltage is available at Q1 Emitter since the four paralleled gate outputs of the IC go therefore to the high state.
The circuit will start if P2 is pushed for 1 to 5 second and will switch off after about 35 minutes. The time delay can be varied depends on values of R1 and/or C1. If required, P1 will stop the timer. LED D1 is optional. When the load is placed far from the time, LED D1 can be useful to signal relay operation

List Components of Long Delay Timer Circuit :
R1   : 10M
R2   : 4K7
R3   : 1K
C1   : 220µF/25V
D1   : LED any type
D2   : 1N4148
IC1  : 4011 Quad 2 Input NAND Gate CMos IC
Q1   : BC337
P1,P2: SPST Pushbuttons
RL1  : 12V Relay Switch 

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