Thu Feb 14 19:28:00 2013

Caomh Veneficus Gysgodi o gath III

What do I buy my sister for Christmas?

So I'm always a bit stuck for what to get people for presents for birthdays, Christmas, Yule or whatever. This year I came up with an idea of what to get my sister Tracy for Christmas. Some garden lights, but not just ordinary garden lights, RGB ones!

And so the idea began.

RGB LED light strips that can be placed along the garden and have their colour changed as needed. The idea is to make these similar to flourescent strip lights only full colour with the ability to position them however the sister wants them down the length of her garden.

As arbitrary decisions go, I'm choosing to make eight of these.

Buying RGB LED strip

It's simple to buy RGB LED strip, right? Actually, not so much. It took me three attempts. The first two both met with the same problem, these were:

  • ✥ 3 x 5M 500CM 300 SMD LED 3528 Strip Waterproof Flexible Light
  • ✥ 2 x RGB LED Strip light SMD 3528 60 LEDs/M 5M Waterproof

RGB LED strip isn't always combined RGB in the same LED die. Both of the above strips are a reoccuring pattern of red, green, blue all the way along the strip. You're not going to get anything other than one of those three out of these any time soon.

I have a theory that if you want RGB in one die, you need to go to 5050, which on the third attempt is what I did:

  • ✥ 2 x 5050 LED Strip Light 300 SMD RGB Light 5M Flexible 60leds

N.B. this wasn't the waterproof type! The next section explains why.

Not all was lost though as the first one of these I ordered came with a neat infra red control box! That'll do nicely for control. This is the kind of things I'm talking about.

Plastic tubes

So having ordered the wrong LED strip, taken the measurements off the item, I ordered some 10mm outer and 8mm inner diameter acrylic tube. The 3528 LED strip was 8mm wide and the waterproof style with a coating on it.

  • ✥ 10 x 1m lengths of acrylic tubing, 10mm OD, 8mm ID.

Even if these had been the right strip, this wouldn't have worked as the waterproof coating very effectively sticks to the inside of the plastic tubing meaning you can't get more than a small amount down the tube before it jams up and stops moving.

Fail again. And the right LED strip is 10mm wide. Back to the very nice people at Trent Plastics to order some 12mm ID, 16mm OD. 2mm spare will be good and useful.

  • ✥ 10 x 1m lengths of acrylic tubing, 16mm OD, 12mm ID.

I had a little bit of an experiment with trying to frost the plastic with sandpaper on the outside, but it didn't really work. Another suggestion was to sandblast the inside, but running out of time until Christmas I decided to leave them as they came.

Bob 'parag0n' Clough of the Hackspace Manchester had an issue with his spice grinder at home frosting the plastic on using cloves so he suggested this might be another approach. Time didn't let me test this theory.

Sealing the tubes

So having bought the right strip, and the right tubes now I need to seal the strip in the tube. Various theories and ideas on how to do this crossed my mind, but I eventually settled on a simple solution. B&Q sell 15mm compression pipe fittings:

Pipe coupling #1 Pipe cap #1

The problem is that these are 15mm and our pipe is 16mm so we need to make some modifications to make this work. First, we take the coupling apart:

Pipe coupling #2

Dispose of some of the bits as we don't need them:

Pipe coupling #3

Next thing we need to do is to expand the hole in one of the caps and one end of the pipe coupler. I did this with the lathe at Hackspace Manchester:

Pipe coupling #6

We need to turn down the cable gland so that it will fit into the end of the coupling that we didn't make bigger:

Cable gland #1 Cable gland #2 Cable gland #3 Cable gland #4

Same for the cap, expand the hole and the nut so now we should be able to attach these to the ends of the pipe:

Pipe coupling #7 Pipe cap #2

Now we can measure the strip:

Measuring the strip #1 Measuring the strip #2

And cut it:

Cutting the strip #1 Cutting the strip #2

You'll note from the second photograph above that I've cut the strip quite close to one end of the exposed copper, that's to make the next section easier. Now we need to push the strip into the tubes with the exposed contacts going to the end with the cap:

Inserting the strip #1 Inserting the strip #2

Connecting to the LED strip

The controllers are capable of driving 6A maximum, so I'm assuming that's 2A per colour. They will happily drive a 5m length so we'll need to use two controllers with 4m of strip attached to each controller. A nice convenient cabling for this was again suggested by Bob 'parag0n' Clough, Cat5 cable. A damn fine idea that man! Once again I e-bayed up the wrong thing... kind of... facepalm

So, external grade Cat5 can be bought for about £45 from e-bay for a 305m box. Not a bad price. The problem was what I ordered was solid core cable and not stranded, designed for punch down to face plates and patch panels. It's not ideal for soldering, but onwards! We push the cable up the back of the strip:

Cable insertion #1 Cable insertion #2

I needed to connect it. I recently purchased a selection of boot lace ferrules from e-bay for a different project, so I crimped the ends of the Cat5 into the ferrules:

Cable termination #1

Now that we've got those crimped into some ferrules we can coat the ferrules with resin, tin them, tin the strip end and then solder them together:

Cable termination #2

Next we assemble the cable gland at the bottom:

Cable gland #5 Cable gland #6

All screwed together:

Cable gland #7

Next time, I'll talk about power supplies and wiring it all together.