time delay relay circuit schematic

555 Time Delay Relay Circuit

This time delay relay circuit is built with IC NE/SE555, produced by Intersil which contains a precision timer. Stability to temperature variations is 0.005 %/oC. In the circuit diagram, the IC works as a monostable multivibrator. It is set by operating the key Dr1. With Dr2 you can reset the assembly any time you desire.

Time delay relay operation

Pin 3 provides (after setting) a positive rectangular pulse, whose amplitude is approximately equal to the 12V power supply voltage. This output should not be charged with more than 200 mA over a period of time.

Pulse width can be calculated with the formula:

t = (R2 + Rp1)*Cs1

In this formula t is in seconds if the R2 and Rp1 values are set in ohms and Cs1 is in Farads. Cs1 is the switched capacitor to potentiometer P1 by the S1 switch. Lighting time is set roughly in the decade with S1, while P1 serves to fine tune.

Time delay:
S1a = 0.1 … 1 s
S2b = 1 … 10 s
S2c = 10 … 100 s
S2d = 100 … 1000 s
S2e = 1000 … 10000 s

For the Reed relay, by whose contacts the lamp is connected and disconnected, the following conditions must be met: operating voltage does not exceed 12 volts and current draw is not greater than 200 mA. If Reed relay’s working voltage is below 12 volts, then you can connect a resistance Rx in series with the relay’s coil.

Eventually it can be used a triac in place of the Reed relay. In this case the gate is controlled by Rx (here Rx = 150 ohms).

You should to consider a proper insulation of the time delay relay installation and wiring.

Time delay relay circuit schematic

time delay relay circuit schematic


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  • Joel

    Similar to Ed, I’m looking for a delay on/delay off circuit — Controlling a pump, the input (a pressure activated switch) tends to cycle for a few seconds after either an on or off action and i want to damp out these oscillations after *either* transition. This circuit gets me half way there….any ideas for ther other half? -J

  • Sudharson

    Hi……….. i want 6 hour timer circuit diagram. HELP ME please….


  • artois

    Ed How long do u want the circuit to stay on before turning off and do u want this to cont all the time off on off etc

    • Yen


    • Ed

      Well technology got me, I lost my computor due to virals. So a belated thank you for your response. I got it too work, I found one on “chemelecs” electronics projects page builf it, analyzed why it works and move into modification of a simpler single 555 version of my own. The it work fine on the bench,,I found it lose its stability in the truck I built it for too siwtch on and off and on a relay conected EFIE,, “electronic fuel injection enhancer” installed in series w/ O2 sensor to OBC,, think it was picking up “hysterious?” Any Idea?

  • Ed

    I asked that question on thee 10th of November, 2010,,, today is thee, 31st of December 2010. After almost two months I have tried various other design’s via transistor and thee ever famous 555. I have yet to finish a totally simple circuit, because I HAVE NO EXPERIENCE, and have no ANSWER TO MY 1st question. WHATS THE POINT OF THIS PAGE IF NO ONE MONITORS IT?

  • Ed

    Heloo, NICE circuit idea ! Can you or someone please tell me, will this re-set itself? Meaning, we know it will delay the on time, but will it also delay off time as well and restart the cycle? I guess I could build two seperate circuits to re-set it but seems like it would be a waste to do so if modifictions already exist to accomplish the same results,,Thankyou

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