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Looking for a specific light-activated switch (12V DC)

WangDangler

Dec 2, 2022
4
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Dec 2, 2022
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Working on a project and it requires a light-activated switch. Every light-activated switch I can find opens the circuit (power off) in the presence of light - I actually need the opposite! I need a sensor that will close the circuit (power on) in the presence of light. Preferably with adjustable sensitivity. Does anyone know what I could use for this, besides building a complicated circuit with custom programming?

I have both size and time constraints so I can't really go the arduino/maker board route.

Any ideas?

Thanks for any help!
 

Minder

Apr 24, 2015
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3,335
Wide open question!
What is the application?
Stand alone unit or circuit board mounted etc..
There are many that offer both options.
What is the sensor operating in to?
 

WangDangler

Dec 2, 2022
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Dec 2, 2022
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Maybe I should have explained the entire project to make it more specific.

I work in a sales environment where the person who can answer the phone most quickly makes the most money. It has gotten to the point that simply sitting at your desk isn't enough, some people are sitting there with their hand on the phone waiting for a call. No incoming call gets answered in more than a second. I would like to create a physical device that pops the phone off of the hook to answer the call faster than the people who are sitting and waiting for calls to come in.

I am limited with what I can do because the company I work for owns the phones and I cannot hardwire anything to the phone itself, so I'm limited to answering the phone via the speakerphone button, or lifting the handset itself.

My idea was to create a simple little invention that triggers a motor device to either push the speakerphone button or lift the handset, triggered with a sensor that reacts to the ringtone of the phone or the light that flashes when the phone rings. I chose to pursue a light-activated device because I work in a noisy environment and it would be hard to tune something that reacts quickly to just the ringtone of my desk phone and not mistakenly activate with these noisy co-workers.

I figured that I would make it basic as possible - using some kind of basic light-activated switch device to turn some kind of motor or small pneumatic device on via a power supply, lifting the phone off of the hook at a rate faster than that of my coworkers. And while it doesn't have to be a tiny or discrete device, it has to fit on a sales desk in a professional setting and it can't look sloppy or questionable.

Is this a stupid idea? Probably. But in a situation where answering the phone 0.1 seconds faster than my co-workers often results in a difference of thousands of dollars, I'm willing to give it a try! Thanks so much for your folllow-up!
 

Bluejets

Oct 5, 2014
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Usually in a basic ldr, change position of the ldr with respect to it's voltage divider mate.
 

danadak

Feb 19, 2021
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Feb 19, 2021
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Detection of light could occur within mS of turn on. Driving a solenoid
that can push handset up < 100 mS a little challenging, due to inertia and
force required. You would need some experimentation. I can see a wall wart
supply fine for application. Could be done with a ATTINY85 type solution,
something like this, and a SSR or power mosfet to drive solenoid. ATTINY85
board :

1670072907708.png
Just curious, why would management / associate workers not challenge the
use of this ? Or use one themselves and then you are all on equal footing
again ?

Rough code to run ATTINY85. mBlock takes your code block configuration and
turns that into Arduino (ATTOINY85 compatible) code and you program the card
with that.

1670073781091.png

Basically would look like this :

1670078384760.png


Regards, Dana.
 
Last edited:

WangDangler

Dec 2, 2022
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Dec 2, 2022
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Put double-sided sticky tape on everyone else's cradle.....
I have thought of injecting a little superglue in everyone else's speakerphone button. I'm trying to exist in that gray area and not resort to sabotage yet:cool:
 

WangDangler

Dec 2, 2022
4
Joined
Dec 2, 2022
Messages
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Just curious, why would management / associate workers not challenge the
use of this ? Or use one themselves and then you are all on equal footing
again ?
I'm very conscious of the fact that this device may not be allowed long term... but it will provide a good laugh and may give me the edge for a while! Other than that I just think it could be a fun project, and as long as I'm not damaging company property, this is not inherently wrong, so I'm going to just ask for forgiveness on this one!
 

hevans1944

Hop - AC8NS
Jun 21, 2012
4,780
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Jun 21, 2012
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I once worked with an engineer whose office was located some distance from the laboratory where he normally worked, often late into the evening. His wife would call his office phone but he wasn't there to answer it, so he needed some means to notify himself in the lab when his office phone was ringing. The clever solution he came up with was a cadmium-sulfide photo-conductive sensor cell, optically coupled to one the buttons on his office desk phone (there were five illuminated button IIRC). He used the opaque red or black rubber cover from a large alligator clip (which had a standard banana jack profile on the non-gripping end) to attach the photocell to the appropriate button. The rubber cover also shielded the sensor from ambient light. He then ran a pair of wires (very small gauge!) from the photocell out through the small hole in one end of the rubber cover to his laboratory. He attached a 6V lantern battery and a doorbell, wired in series, to the pair of wires. Voila! Office phone rings, CdS cell resistance drops, doorbell in laboratory rings.

All the phones on campus were connected via a Centrex system, so the same button for a given line would light up on all the desk phones in a department. The phone in his lab had the bell disconnected, to avoid disturbing him from callers on the other four lines, so the doorbell arrangement allowed him to answer calls to his office phone from the lab phone.

I would modify his arrangement to include a small solenoid instead of a doorbell. The solenoid, when energized, would slightly lift the handset from between the two cradles just high enough to "answer" the phone. You could also go for a non-electronic solution using a rubber bulb (like the kind used to pump up a blood-pressure cuff) to inflate a small bladder (balloon) placed between the handset and the two cradles. I would place the inflation bulb on the floor, to be operated with your foot as soon as you hear or see the phone ringing.

so I'm going to just ask for forgiveness on this one!
Always easier to ask for forgiveness instead of asking first for permission!
 
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