Questions about the Time Delay

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Joined: Wed Nov 09, 2016 2:34 am

Questions about the Time Delay

Post by mini » Sat Jun 24, 2017 8:36 am

Hello, all~
I have made a time delay relay built with IC--SE555. The time delay relay circuit schematic is given below.And now I’d like to ask about two simple modifications.The schamatic diagram is given below.
SE555 datasheet
A). I want a roughly 10 to 45 minutes timer,can I eliminate the a-d S1 capacitors with no problems? eliminate the switch and direct-connect the 4700microF

B). How can I add an indicator LED light to show it is ON? That is, a red light when the relay is connected and 220V on the external load (a heater)

Thank you.

Posts: 202
Joined: Sun Oct 04, 2015 6:18 pm

Re: Questions about the Time Delay

Post by David » Wed Jun 28, 2017 4:02 pm

a) Yes, quite OK to remove switch and connect 4700uF to pins 6 & 7 and the pot.
b) The easiest way is to connect a led in series with a 1k to 1.5k resistor from pin 3 to ground. The led will light up when the coil of the relay is energised. BTW, it is usually good practice to connect a diode (1N4000 or similar) across the relay coil with the anode to ground and the cathode to pin 3. This is to suppress the back emf spike when the relay de-energises. Take care with getting the diode in the right way round!

Hope this helps.

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Joined: Wed Oct 11, 2017 10:16 am

Re: Questions about the Time Delay

Post by ThomasRes » Sun Oct 22, 2017 4:15 pm

I never knew you could safely remove switch and connect 4700uF to pins 6 & 7. Thanks for the info David.

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