# HELP: Break Beam Switch using IR LED/rec (long)

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#### funkmasterta

##### New Member
I'm an electronics newbie and I was wondering if someone could help me with this idea. How would you create a break beam type switch from an IR LED and an IR receiver?

I've been wanting to add some lighting to the storage compartments in the front doors of my car so that at night, we don't have to use the map lights to find stuff in there. I was going to do a simple LED + switch setup but thought creating motion-activated LED lights, ie, so that when your hand enters the compartment it lights up automatically, would be way sophisticated and Star Trekky...sort of like those Bang & Olufsen home audio systems that open the glass covers when you swipe your hand over a sensor.

My first thought was to mod those ~$10 motion sensors at Home Depot (or your fav home improvement store). Details on how to mod and get it to operate on DC voltage here: http://www.thebells.net/Halloween/PIR_Mods.html But, ran into 2 problems: 1) Units are way too big to fit behind the door panel 2) the FAQ says it runs on 18v DC, car power source is 12v DC But then a better idea came to light (no pun intended). Couldn't we just use an IR LED in conjuction w/an IR receiver and set it up similarly to those door entry chimes you see in small shops, ie, when someone enters the door, it breaks the "beam" and chimes a bell. IR LED's are about$1 each and I'm sure the recievers wouldn't cost much more. It would be nice to be able to add some capacitors so that it "fades" on and off like the dome lights.

Any ideas on how to get this started?

Thanks a bunch!
-Tom

#### Scubasteve

##### New Member
Hey..

I am not sure what you need exactly, but I will offer some suggestions.

If you want to make an infrared switch, it isn't complicated. You simply choose which ones you want, power it properly (ie. through a regulator from 12V). Then make sure that it is will shielded so that you will minimize daylight interference, which contains a lot of infrared. Some people even go through the length of modulating the IR with 40KHz and making sure that the recieved light to be valid is also at 40KHz.

Motion detection is a different story and is a lot more advanced. You should ask yourself what you really need

Steve

#### funkmasterta

##### New Member
Thanks for the suggestion. How would I go about creating an IR switch because that would probably work best with this application because it'll only be used at night. I found some parts at Rat shack

Catalog Number: 276-145 IR LED

Would those work?

#### Scubasteve

##### New Member
The LED is hooked up as usual. You need a fairly regulated supply, which you know the voltage of. Then you take the LEDs forward voltage drop and subtract that from your supply (ie 12V), then take the recommended current and divide this voltage by it in order to find the appropriate drop resistor.

Recieving is a different story. Basically,, you need to take the output off of the emitter and through a resistor to ground. This will cause a variable voltage off the top of this resistor to work with. I guess you can use this with a comparator with a reference to trigger whatever you want..

Let me know if you need more help,

Steve

#### Inaweofitall

##### New Member
I too am an electronics newbie. I am trying to learn what all the symbols mean so I can build a circuit (?)- device. I am trying to build something similiar to what funkmasterta is describing. Hopefully
there is a moderately simple way to build a device, using a infrared LED , focusing it onto a IR receiver modual that is 12 to 18 inches away. If a small laser would work that would be fine.
I hope to power it with 9v to 12v, preferably 9v.
When the beam is broken the switch activates a small solinoid. The solinoid needs to move only about 1/8". I need it to operate in daylight or in the dark. It would be preferable if the unit was about
the size of a pack of cigaretts.

Thanks
Stephen

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