![]() 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. 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.
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