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Set timer to 1 minute4/9/2024 If very long time delays are required it is not advisable to use 555 timer.Instead one can use a microcontroller. This circuit is used in such applications where cyclic operation is required.This can be achieved by adding a level sensor such that this sensor input drives the reset and inhibit pins towards the ground potential. ![]() Suppose if there is adequate water in the tank, the pump must be turned off automatically.It can be ON until cooler mats are wet and then it can switched off.Again when they are dry it should pump the water.For example in air coolers,there is a pump that pumps water to the mat.This need not be switched on continuously. Let us understand the application of this circuit.It is also possible to add a sensor or switch at reset input of decade counter for automatic turning off the load in emergency or needy (for an automatic operation) situations.Therefore, ON and OFF can be varied for desired duty cycles by appropriately connecting the pins of decade counter.Suppose in this circuit 3 outputs of CD4017 are used.So,On time of load is 3 times of T (high) and off time is 9 times of T(high).Here the length of ON-time of the load is a multiple of 555 timer period output and number of outputs used in CD4017.(Instead of 6v relay one can use 12v relay also but relay should be applied with 12v instead of 6v.) The outputs of the decade counter drive the transistor into active mode so that relay coil will be energized.This square wave is given to CD4017 IC decade counter which has 10 outputs activated sequentially upon a given clock input.It gives a pulse width according to value of pot.When the power supply is given ,555 timer produces square wave at pin 3 as it is in astable mode.Let us discuss in detail about this circuit. These on off intervals can be adjusted by varying the 555 timer output and number of counter outputs. This circuit uses very basic components like 555 timer and 4017 counter. In this circuit a timer with cyclic on off operations is designed. Adjustable ON OFF Timer(using 555 astable mode) Some 555 versions may get damaged because of this.To prevent 555 timer from flyback current in the relay use a diode before the relay.This circuit is used in such applications where the load is switched on for sometime and is off for rest of the time.Thus relay will be on for required amount of time set by the user using pot and then it is switched of automatically.A 12v relay is used to drive the ac load connected at the output.Hence time T=120k*470uf=6 2 seconds~1 minute (approximately).For minimum time place the pot in least position.Then R= 120k.T= 1.2M*470uF = 620 seconds≈10 minutes.This is the maximum time. When Pot is maximum R is 120K+1.1M ≈ 1.2M (approximately) and C1=470uf.Time period can be calculated using formula.The above proposed circuit is a 1-10 minute timer.When Pot is minimum it gives 1 minute delay,where maximum value of pot can produce 10 minutes.This pulse width depends on R and c values. When the trigger input is applied,555 timer produces a pulse.Here 555 timer is operated in monostable mode.This circuit is flexible to adjust required time. ![]() Using simple 555 timer we can design an adjustable timer switch. Simple Adjustable Timer Circuit with 555 IC
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