Photoelectric sensor: reversing the on/off function


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Old 04-13-16, 02:08 PM
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Photoelectric sensor: reversing the on/off function

Hi,
Attached is a picture of the photoelectric laser sensor I took apart. I'm using it to turn on and off a computer fan but its factory design is opposite of what I want. When the laser is impeded the fan goes on, when the laser hits the receiver (the attached) the fan goes off. I'd like it to work the exact opposite and wondering if it's possible to change it somehow.

It currently operates by connecting the the black wire shown with my black fan wire, the brown shown with my red fan wire and one power source (12V DC), the blue wire shown with my other power source wire. I've tried all combos of switching wires to see in the desired effect occurs but it only operates with this setup.
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Any advice would be helpful, I'm quite illiterate in home electronics fyi.
Thanks,
R
 
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Old 04-13-16, 03:23 PM
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You could use a normally closed relay to control the fan and the laser to control the relay. When the laser control feeds power to the relay the fan will turn off.
 
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Old 04-13-16, 05:33 PM
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You could definitely change two parts on that board to do what you want but since they are surface mounted parts.... you'd ruin the board replacing them.

Ray's idea with the relay is the best way to accomplish what you want to do.
 
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Old 04-14-16, 11:01 AM
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That's terrific Ray, thank you. I'm in Toronto and there aren't many stores that pop in my mind that might sell the relay needed, not that I'm familiar with the market. Could you suggest an item online or what exactly I should be googling.
Thanks so much. I'm excited to try it out.
 
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Old 04-14-16, 11:09 AM
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You could try looking for normally closed relays with 12 volt coils on Ebay. We will be glad to take a look at what you find.
 
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Old 04-14-16, 06:03 PM
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Amazon: 12Vdc Relay Normally Open/Normally Closed Relay

amazon/SPDT-Relay-Board-Single/elk912

Elk Products 912 Relay 12VDC 7A 10A SPDT | eBay

The top link is just a relay.
The second two are relays on a board with set screw connections. (my personal choice)

You can use ANY 12vdc SPDT relay. You can enter that in your search engine and find many hits.

A real bargain...
10pcs 12VDC General Purpose Relay 5 Pin SPDT | eBay


This style of relay is used heavily in auto applications. It comes in a 4 pin(SPST) version and a 5 pin(SPDT) version. You must use the 5 pin version. The link is for two with wire harnesses. You can find these relays in most any auto parts store too.

Auto 12V 40A 40 A SPDT Relay and Socket 5pin 5 Wire | eBay
 
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Old 04-14-16, 06:13 PM
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It currently operates by connecting the the black wire shown with my black fan wire, the brown shown with my red fan wire and one power source (12V DC), the blue wire shown with my other power source wire.

So based on that.....
black is the switched - output from the module.
red is the + to the module
brown is the - to the module.

Can you confirm that.... as it doesn't follow logical wiring methods.
Do you have a part number of that device or a wiring diagram ?
 
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Old 04-15-16, 07:26 AM
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Hi PJ,
The sensor I have is exactly this one: M12 Through Beam Photoelectric Sensor Laser Beam X1PAIR | eBay

And my computer fan has a black and red wire.

So a 5 pin relay at an auto parts store I shall buy, I'm not sure which wires will go to which pins but trial and error will get me there I hope lol. Thanks so much for the info.

Richard
 
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Old 04-15-16, 11:37 AM
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The relay will have the numbers stamped on it. They sell the plug with wires that may make it easier. If not.... you can use 1/4" push-on terminals to fit relay.

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Last edited by PJmax; 04-15-16 at 11:55 AM.
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Old 04-15-16, 11:48 AM
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Fantastic. You rock PJ! I will report back once I get the relay and test it out. Thanks very much.
 
 

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