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help ID IC used for dusk/dawn controller

bid215

Sep 17, 2022
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My wife purchased a fairly expensive outdoor clock that is supposed to light up at night. It uses a ring of LEDs illuminating the plastic dial face, using a photo-resistor based circuit powered by C cells. The clock will only light up when there is a fast transition from light to dark, like turning off the porch light after sunset. It will not turn on from the slow sunset darkening. We contacted the supplier who immediately sent a new clock, telling us to just keep the original one. The new one behaves the same, and I found many reviews of the clock with this issue noted, so it led me to believe just a poor design.

I removed the control card to do some debug but am stuck trying to identify the IC that the manufacturer blacked out.

What has me stumped is this chip has the positive voltage on pin 1 and the return or ground on pin 8.

The positive rail from the battery connector loops around the top of the pcb and under the IC to connect to pin 1, when they could have simply connected the C1 bypass cap to the adjacent connector pin.

The photo-resistor pulls pin 7 low when in the dark and pin 3 goes low to sink the current for the LED string.

The remainder of the pins are floating.

In a slow light to dark transition, there seems to be a glitch or noise burst with the LED array flashing on then remaining off. With the fast transition LEDs light and stay on. This makes me think the IC is some latching comparator with a floating reference pin, but I have not been able to find such a device. I do not have a scope, so I'm doing this debug only with a DVM.

Any ideas what this part is?

IMG_5384.jpg
 

Martaine2005

May 12, 2015
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Sounds like a 555 timer. But pin 1 is negative and pin 8 is positive. Pin 3 for output.
Could possibly be a microcontroller too, a picaxe or the like.

Martin
 

bid215

Sep 17, 2022
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I was hoping it was a 555, would be easy to solve. Interesting that a PIC has the right power/ground pins. Seems a bit overkill for the task.
 

Martaine2005

May 12, 2015
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This PIC has the same pin out as in your first post.

Martin
 

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kellys_eye

Jun 25, 2010
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AFAIK the 555 won't work at 3V anyway.

The device is, as suggested, a microcontroller so any modification is going to be 'impossible' - certainly not worthwhile. Far easier to build your own dusk/dawn detector from scratch.
 

bid215

Sep 17, 2022
3
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Sep 17, 2022
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AFAIK the 555 won't work at 3V anyway.

The device is, as suggested, a microcontroller so any modification is going to be 'impossible' - certainly not worthwhile. Far easier to build your own dusk/dawn detector from scratch.
I fear that's exactly where I am.

So odd to use a micro, develop code for if 'input 1 is low, set output 1 low' likely with some debounce built in, then maintain an image and have to program devices for production. Then to do it so poorly so it doesn't work. Sometimes analog is just the right answer.

Thanks all,
 

Bluejets

Oct 5, 2014
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I fear that's exactly where I am.

So odd to use a micro, develop code for if 'input 1 is low, set output 1 low' likely with some debounce built in, then maintain an image and have to program devices for production. Then to do it so poorly so it doesn't work. Sometimes analog is just the right answer.

Thanks all,
Take a good look around.
Everything these days from toys to autos to dunny rolls will have embedded uC's installed.
Makes manufacturing sense.
FYI, repair priority of any electronics went out the door some 20 to 30 years ago.
 
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