This is Circuit diagram For ON time Delay Timer. When Give supply to the circuit then connected Load through Relay is Turn ON After a Fix Time Duration. Delay Time Duration Can be changed by the Adjusting Of Preset And Changing the value of capacitor C1. The delay time is getting by using the formula **t=1.1xR1xC1**. This project submitted by [circuitspedia.com](http://www.circuitspedia.com ) In this project 555 timer is used which is very popular and this is most useful in making of any Delay Timer, Multivibrator etc. This circuit is useful in protection of any device from sudden unstable and unregulated supply, Because sometime very high voltage come and take some moment to Regulate at required level, In this timing taken by supply to maintain the required level any device can be damaged. so this delay on timer circuit is used to provide a delay time duration before switch ON any device .  **working** In this circuit the 555 timer ic is connected as Monostable Mode To provide ONE SHOT output. In Monostable mode the output is HIGH for a fix time and after that time output goes to LOW Automatically. so When output is HIGH (ON) the transistor Q1 is ON and There is negative supply (0v) At the collector of Q1. In this case the transistor Q2 in OFF state because the base of Q2 is connected to Q1 and then this is ON the Voltage at BASE of Q2 is 0v . So when transistor Q1 is ON the Tranasistor Q2 goes to OFF . After a fix time when Output from 555 is LOW and Q1 Turn OFF . Therefore the Transistor Q2 Turn ON and then the relay is activated and then the Load is also switch ON. The delay timing duration can be changed by the adjusting of presetor changing capacitor value of c1. Delay timing Duration can Found using T=1.1R1C1 For More Interesting Project and circuit diagram ** [Click here](http://www.circuitspedia.com/) ** Also Read **[Delay OFF Timer ](http://www.circuitspedia.com/delay-off-timer-circuit/)**