Thursday, 28 June 2012

Project: Beer Fridge Lighting

Flawed. My new beer fridge, a 50L-odd unheard of brand bought off eBay for $72, was basically brand new and unused. But it had a serious design problem - it was built without an internal light. So you know, when you go to get something from up the back or you didn't turn the light on as you entered the room, you can still see what you're doing. Nope. Ok, so it's a tiny fridge that only holds my beers, so it's hardly be a crime if I get the wrong beer, because it'll still be nice. But I wanted it anyway. Firstly, I nipped down to my usual hangout, Jaycar, and got this: http://www.jaycar.com.au/productView.asp?ID=ZD0462 - which is a 48cm hard strip of white LEDs that can be cut to length and run off 12v DC. Great for cars, boats, computers, etc. The fridge was, at the time, in my bedroom, so I had a few a cables running around.

The beer fridge where it was first placed in my bedroom. Notice the two power 
cable running along the wall.


I used some random speaker wire I had lying around to run power to the LEDs. This wire passed through the small hole in the rear top right corner of the fridge, which was there for the thermostat controls to pass through. When I bought the LEDs, I also asked the guy to provide me with a 12v DC power supply, however he must've been full of shit because it didn't work. Pretty sure it was the wrong one. Power then had to come from an auxillary output from my PC's PSU...which was great as long as it was on. I also had the original plug for the fridge to deal with.

My beer fridge, newly outfitted with about 18 white LEDs to the roof just inside.
 
 
 
Light was now available, but it was a bit crap because I had a few random wires everywhere and the light only turned on when I flicked the switch taped to the roof inside the fridge. It ended up staying like this for about 18 months, until holidays from uni showed up, and I got the chance to attack my ever growing list of projects. A few months back, I went digging. I have a huge box of assorted electric garbage, that every now and then puts out some solid gold. There just happened to be an laptop PSU, which output 12v DC. This was exactly what I needed to be able to run the relays of their own dedicated supply, and through just one plug (instead of separate plugs for the LEDs and fridge). Unfortunately I didn't take any photos of this, but I used something similar to these: http://www.jaycar.com.au/productView.asp?ID=HM3192 - cutting the power plugs off the fridge and 12v DC PSU, I wired their respective wires into shared connectors (earth from the fridge and LEDs into one connector, etc), then used the remaining fridge plug/cable to complete the circuit. Now the fridge and LEDs were running off the one plug. And this worked great. The last problem was having the LEDs operate like normal fridge lights - on when the door is opened, off when the door is closed.

I considered relays, and mounting momentary normally closed push button switches, but because of the design of the fridge door, there was really no easy way to mount it. And I wasn't too keen on drilling into the walls of the fridge, and potentially destroying the whole thing. Reed switches. While trolling the Jaycar site, I came upon this bad boy: http://www.jaycar.com.au/productView.asp?ID=LA5074 - a very small, normally open reed switch. Whilst it was backwards for my needs (circuit is open when the magnet moves away), I could use a 5 pin automotive relay to wire it in the opposite direction.

Circuit diagram plan - the text at the bottom refers to the normal operation of 
these kind of relays. The diagram is correct.
 
 

The plan was to have the relay switch the 12v DC output to an open pin when the magnet closed the reed switch, so that the LEDs would not operate. When the magnet moved away from the reed switch, power moves to the normally open pin - but actually goes to the LEDs and powers them up. Pretty standard operation of a relay I guess, but I think it's pretty cool. With that, check out the picture.

 LEDs in operation with reed switch and relay; notice the reed switch and magnet in the 
top right corner of the fridge?


And that's it. Pretty simply project I guess. The wiring for the reed switch unfortunately runs on the external top surface of the unit, so it's held down by copious amounts of duct tape. The relay is zip tied to the chassis, along with the 12v DC PSU and merging connector block. Many, delicious beers...


-Tim

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