![20 minutes timer 20 minutes timer](https://i.ytimg.com/vi/SxVwYHFMRn0/maxresdefault.jpg)
There are flaws with the circuit, the 10K resistor top left is simply connected all the time between +9V and ground -ve rail thereby drawing power for no useful purpose, you need to connect 10K bottom leg to the pin 2 of the 555 timer, so that it is held at 9V+ through this 10k (pulled high) so when you push the switch then pin 2 goes low (-ve) to trigger. LED will be ON initially (OUTPUT PIN 3 LOW), as soon as we press push button (trigger the 555 via TRIGGER PIN 2), the timer will start, and LED will become OFF (OUTPUT PIN 3 LOW), after the calculated time duration, PIN 3 will again become LOW, and LED get turned ON.
![20 minutes timer 20 minutes timer](https://shop.dkoutlet.com/media/catalog/product/cache/2/image/9df78eab33525d08d6e5fb8d27136e95/T/T/TTM20_L.jpg)
So we have calculated OFF time above, means after the calculated time LED will be turned ON. We should note here that we have used LED at reverse logic, means when OUTPUT pin 3 is low, LED will be ON, and when OUTPUT is HIGH then LED will be OFF. Similarly to create a 10 minute timer we would be changing the resistor value to 545.4 k ohm.Īs per above calculations, for a 15 minute timer circuit, we need the value of resistor to 818.2k ohm. So to build a 5 minute timer circuit, we would be simply changing the resitor value to 272.7k ohm in above given 1 minute timer circuit. We can easily calculate the resistor value for 5 minute, 10 minute and 15 minute timer circuit: So to build 1 minute (60 seconds) timer we need resistor of value 55k ohm and capacitor of 1000uF: In monostable mode, the duration for which the PIN 3 would remain HIGH, is given by the below formulae: We need to set 555 timer in Monostable mode to build Timer. All we need to change the value of Resistor R1 and/or Capacitor C1. We can use this property of 555 timer to create various timer circuits like 1 minute timer circuit, 5 minute timer circuit, 10 minute timer circuit, 15 minute timer circuit, etc. It means for some time output pin 3 is HIGH and for some time it remains LOW, that will create a oscillating output. As the name suggest 555 timer is basically a “Timer”, which create an oscillating pulse.