i need some help with a 741 op amp.

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dacflyer
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i need some help with a 741 op amp.

Post by dacflyer » Fri Aug 04, 2017 12:42 pm

i have been playing with these for sometime now, mainly for light / dark relays for solar lights i build.
i was having a issue with relay chatter right as it got dark, but i fixed that with a resistor ( hysteresis control )
but i am looking to add a bit more to it,, i am looking for a way to add in some delay, so that if it a passing cloud or such does not trigger it to come on, then back off right away..or any other shadow, have had a few times just before dark and a passing cloud would make light come on, then go back off after a few seconds..
any ideas? i'd like something to give me about 15 to 30 seconds delay before transitions.. is this something that can me added to the 741 circuit or will this require another separate circuit ?

this is all 12vdc operated circuit, the circuit drives a relay.

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Lenp
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Re: i need some help with a 741 op amp.

Post by Lenp » Fri Aug 04, 2017 1:04 pm

How about a large value, low leakage capacitor, directly across the sensor to slow down the swings from the light changes? :idea:
Or add a filter to the sensor lens to tame it down a bit.
No, I don't think there is an optical capacitor :sad:
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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jwax
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Re: i need some help with a 741 op amp.

Post by jwax » Sat Aug 05, 2017 6:25 am

Seems like ideal application for a 555 timer. The sensor, instead of triggering the relay, would start the timer, and any new burst of light would keep resetting the timer. Then, if enough time passes without light, the timer would trigger the relay.

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dacflyer
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Re: i need some help with a 741 op amp.

Post by dacflyer » Sat Aug 05, 2017 9:04 pm

i'll try the cap on sensor...

i am trying to see if i can keep it down to just 1 chip.. space constraints

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haklesup
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Re: i need some help with a 741 op amp.

Post by haklesup » Thu Aug 10, 2017 1:07 pm

you want comparator and timer function in one chip, then an 8 bit uController with at least one comparator or voltage detect built in might do the job, maybe don't need a comparator, just an A/D should be enough. Just passively connect the sensor to the A/D input, monitor voltage and execute code with delays included to decide what to do with the I/O pin connected to the relay. Microchip ATtiny can do most of that in a 6-8 pin package. I don't think you can do this with one analog chip, I don't know one with comparator and timer in one package but there might be one, maybe you can find a way with a dual or quad op amp device

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