Instant on, delay off

DerStrom8

Joined Feb 20, 2011
2,390
You can do that with this circuit here. Once power is applied to the circuit, the load comes on for a set duration then turns back off, even though power is still applied to the 555 circuit. If they leave the light on, then when you return to the barn, you simply flip the switch down then up to reset the circuit. Output will be relay contacts. You can adjust the duration by raising the cap value from pin 2 to ground. Go high as possible for more minutes, or increase the resistor values.

Circuit here:
https://www.youtube.com/watch?v=q1Gj_mkMcI0
That's just another 555 monostable circuit, which we've discussed already. It's not reliable for long on-times, which is why people have recommended the 4060.
 

DerStrom8

Joined Feb 20, 2011
2,390
several minutes up to an hour. This circuit will work fine for that purpose.
It will probably work (which is why I posted an almost identical circuit a while back) but it will not be very reliable. That's why everyone was suggesting the 4060 option instead.
 

ScottWang

Joined Aug 23, 2012
7,397
You can delay hours with a 555 timer. A C value of 330uF and an R value of 10 meg will give you just over an hour (3630 seconds) before shutting off. Set it up with a relay and you're set.



Just remember that the Trigger pin must be connected to ground (ideally through a pushbutton switch with a pull-up resistor) to trigger the output.
If you using Ne555 with 15V, Rmax = 10MΩ, if you using with 12V, rate=12V/15V=0.8=80%, Rmax=10MΩ*80%=8MΩ.

The 7555 should be higher to 20MΩ when you using with 15V, rate=12V/15V=0.8=80%, Rmax=20MΩ*80%=16MΩ.

So you have to using 7555 not the NE555.
 

Alec_t

Joined Sep 17, 2013
14,280
Whatever the flavour of the 555, ScottWang, the problem is electrolytic capacitor leakage current; not resistor value.
 

ScottWang

Joined Aug 23, 2012
7,397
Whatever the flavour of the 555, ScottWang, the problem is electrolytic capacitor leakage current; not resistor value.
Thanks, I knew that, but I just mentioned that according to the datasheet the resistor don't used that high in 555, that's all.

For the timer that I love to using CD4060 and CD4013 to be a one second timebase it's more precisely, unless the pepole don't care about the precision, otherwise I will suggest that.

NE555 is common IC and easy to use, so many people like to use it, but I like to use it in a simple oscillator.
 
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