Photocell Question
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Post Fiend
Joined: Mar 2004
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From: San Francisco, Ca.
Photocell Question
Can anyone here tell me how to wire up a photocell to a clock.
I have a wall clock that has a battery operated ''bim-bam'' mechanical movement that has an on/off switch to silence the chimes.
Problem is that the switch is on the movement.
I can't switch it on & off without taking the clock on & off of the wall.
I would like to install a photocell so that the chimes turn off automatically at night.
It wakes me up every 1/2 hour. I had to turn it off.
I bought a package of photocells from Radio Shack, but it came with no instructions.
I tried a google search, but came up short.
Any help with either instructions or a link to a website would be appreciated.
Thanks
I have a wall clock that has a battery operated ''bim-bam'' mechanical movement that has an on/off switch to silence the chimes.
Problem is that the switch is on the movement.
I can't switch it on & off without taking the clock on & off of the wall.
I would like to install a photocell so that the chimes turn off automatically at night.
It wakes me up every 1/2 hour. I had to turn it off.
I bought a package of photocells from Radio Shack, but it came with no instructions.
I tried a google search, but came up short.
Any help with either instructions or a link to a website would be appreciated.
Thanks
Junior User
Joined: Oct 2005
Posts: 85
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From: Lethbridge,Alberta,Canada
I could be wrong but the way I would try it is by replacing the switch in the circuit with the photocell. Basically, just take the wires off the switch and solder them onto the photocell leads.
Posting Guru
Joined: Jun 1999
Posts: 2,007
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From: Oregon
I'm assuming you bought photoresistors, (little round thing with a couple leads), not photocells,(like in solar panels).
Your photoresistor has a high resistance when in the "dark". Basically, it acts like an open. When light hits it, the resistance drops. I can't say it's a short, because they usually have some resistance and using it in a room with various light, (like, full sunlight or table lamp, indirect), will make the resistance vary.
You could try just replacing the switch with your photoresistor, but my concern would be that the only time your chimes would work would be when you have direct light, shining right on it. The voltage on those clocks are usually 1.5 to 3Vdc and that doesn't leave much room for voltage drop.
If it was me, I'd go ahead and do the bypass wiring, (just have your leads sticking out the back), and try just the photoresistor - see how it works. If you aren't happy with it, I'll draw up a simple relay scematic and send it to you. Radio shack would have the parts.
Your photoresistor has a high resistance when in the "dark". Basically, it acts like an open. When light hits it, the resistance drops. I can't say it's a short, because they usually have some resistance and using it in a room with various light, (like, full sunlight or table lamp, indirect), will make the resistance vary.
You could try just replacing the switch with your photoresistor, but my concern would be that the only time your chimes would work would be when you have direct light, shining right on it. The voltage on those clocks are usually 1.5 to 3Vdc and that doesn't leave much room for voltage drop.
If it was me, I'd go ahead and do the bypass wiring, (just have your leads sticking out the back), and try just the photoresistor - see how it works. If you aren't happy with it, I'll draw up a simple relay scematic and send it to you. Radio shack would have the parts.
Last edited by Howdy; Nov 11, 2005 at 12:07 PM.
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Post Fiend
Joined: Mar 2004
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From: San Francisco, Ca.
I did buy a package of "Cadmuim-Sulfide Photocells from Radio Shack (part #276-1657).
They are the little rounds things with a pair of leads sticking out of them.
Sounds like I bought the wrong items.
I'll have to see if Radio Shack has photo-resistors.
I know the photo-reisitors on night lights work in the opposite fashion as the clocks do.
Are both called photo-resistors? and how do you determine which one to ask by name?
Thanks
They are the little rounds things with a pair of leads sticking out of them.
Sounds like I bought the wrong items.
I'll have to see if Radio Shack has photo-resistors.
I know the photo-reisitors on night lights work in the opposite fashion as the clocks do.
Are both called photo-resistors? and how do you determine which one to ask by name?
Thanks
Posting Guru
Joined: Jun 1999
Posts: 2,007
Likes: 0
From: Oregon
Oh no, you've got the right thing...
According to the info on the Radio Shack site, the package you bought has various values. Does it show the value on them? If not, you might need to take your multimeter and see what the min and max is for each.
Use average light and see which one has the lowest resistance, (on), then I usually use my thumb or a piece of tape to cover the window to check for the highest resistance, (off). Depending on your multimeter, you might have to run your scale up in the meg ohms to see this high figure. To test if we can just use a photo resister in place of the switch, you need to find the one that has the lowest resistance while the light is on. We're looking for around 200 Ohms or less. The lower the better. When you find this one, see what it does under various light situations.
The solar lights can use these, or they can use solar cells to switch at night. There's a million different ways to hook this electronic stuff up, which can make it handy or confusing, depending on how hard you make it. I like it easy..
According to the info on the Radio Shack site, the package you bought has various values. Does it show the value on them? If not, you might need to take your multimeter and see what the min and max is for each. Use average light and see which one has the lowest resistance, (on), then I usually use my thumb or a piece of tape to cover the window to check for the highest resistance, (off). Depending on your multimeter, you might have to run your scale up in the meg ohms to see this high figure. To test if we can just use a photo resister in place of the switch, you need to find the one that has the lowest resistance while the light is on. We're looking for around 200 Ohms or less. The lower the better. When you find this one, see what it does under various light situations.
The solar lights can use these, or they can use solar cells to switch at night. There's a million different ways to hook this electronic stuff up, which can make it handy or confusing, depending on how hard you make it. I like it easy..
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Post Fiend
Joined: Mar 2004
Posts: 24,418
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From: San Francisco, Ca.
Thanks guys for the response/help. 
Now I'm off to the garage to find my 550 giga-watt soldering iron, lineman pliers, sawzall, 50 ton arbor press, chop saw and 2 lb. ball peen hammer to work on this project.
Now I'm off to the garage to find my 550 giga-watt soldering iron, lineman pliers, sawzall, 50 ton arbor press, chop saw and 2 lb. ball peen hammer to work on this project.
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