Thursday, 24 January 2013

Tutorial - Adding LEDs to a No-Access Structure

Since I have been asked a couple times about how to do this I thought I should probably do a tutorial for you all. Note the title specifies 'no-access structure,' this means that models will never be inside this structure, giving us more space to play with. I have some ideas on how to do lights in accessible structures, look out for a tutorial later in the year. (Probably, I need to get some new kits for that...)

So you want to light up a piece of terrain. Here is what you will need:

  1. Soldering Iron and solder.
  2. LEDs, preferably 'through-hole.' (They have long legs, see the picture below)
  3. Battery holder, preferably with integral switch.
  4. Wire, preferably 2 different colours, red and black highly recommended.
  5. Resistors, I will detail what value later.
  6. Terrain to light up, preferably with space to hide battery pack.
  7. Drill and hole saw.
  8. Clear plastic sheet. Blister packs are perfect.
  9. Sand paper, medium grit. (Between 300-600)
  10. PVA glue, hot glue gun or whatever your preference.
Hole saw, 'Through hole' LED & Battery pack with switch
So the first step is to give yourself access through your terrain, in my case a 2 story building. Take your drill and hole saw and carefully cut a hole in the middle of the floor. You don't need a pilot hole for this but be aware that the hole saw will twist and bite easily, be really careful.

With that done you now want to work on the windows. Take some old blister packaging and cut out the large flat piece from the back. Now if you leave it like this then you will clearly see the LEDs, which kind of spoils the illusion. What you want is to make it into a diffuser, which is easily done by rubbing it with sand paper. Start by rubbing in one direction, then when it is nice and scratched up, turn it 90 degrees and sand it some more. This will make it look less uniform and will hide the shape of the LEDs behind your windows.

Before sanding.
After sanding.
With that done you will want to cut the plastic into pieces, making sure they are larger than the window, and glue them into place, I used PVA as the building is made of MDF. Make sure the sanded side is inside the terrain, this will look nicer.

Now for the tricky part. If you have never soldered before you may want to get someone who has to show you how it is done. Alternatively there are probably some videos online to help you. In any case be careful, soldering irons run at 300 degrees (Celsius) which is instant scarring hot.
Take your first LED and set it somewhere stable (I used some clamps for this, it may be worth investing in some if you don't have any) and identify the long leg. The long leg has to connect to +ve on the battery (red lead) otherwise it wont work. DON'T CUT THE LEGS! We need them, trust me. Solder a wire to this leg.  If you have red wire use that. Then solder a different coloured wire to the short leg, preferably black. You will notice I am using grey and brown as I ran out of red and black... Repeat this process for however many LEDs you are using, making sure to use the correct colour on the correct leg.

One LED, all hooked up.
The next step is to select a resistor for the circuit. The resistor is important as it limits the current to the LEDs, which will make them last longer. MUCH longer. Math time! Using the equation below will let you select a resistor suitable for your project. If you need help feel free to drop me a comment at the bottom.

Resistor Value = (Voltage of Batteries) - (Voltage of LED) [varies, usually 1.5-2.5 Volts]
20mA * (# of LEDs)

I am using 4 LEDs, 2 AA batteries and one LED needs about 1.5 volt, so I have 1.5V and a total of 80mA. This means I need a resistor of 18.75Ohms. Now you wont find this on the shelf so we will just round up to 22Ohms. That makes sure the LEDs wont run too hot.

With the resistor chosen you need to solder one end to the red wire on the battery pack. The other end will be soldered to all the other red wires you have, depending on how many LEDs you used. Then you need to solder all your black wires to the black wire on your battery pack.

Commonly known as a rats nest...
It is a good idea at this point to test your LED circuit. This is when you realise that you soldered some the wrong way or that you have bad solder joints. Keep all the bare LED legs apart to prevent any shorts in the circuit. It pays to use fresh batteries for this test too!

I promise it gets easier from here! Now you want to glue your first LED into your terrain, placement is up to you, I am trying to simulate a fireplace, so will be grouping the LEDs together near the back wall, away from the windows.

First LED in place.
3 LEDs to simulate a fireplace
As you can see the LED legs are being used to keep the LED floating in free space. This way you can also reposition them once the glue has hardened to your liking. Don't let their legs touch though! I have also glued the cables neatly to the wall. Next up I have used PVA to glue the top floor to the bottom floor. This is a personal preference thing, I want to keep the structure strong.

Were you wondering what happened to the 4th LED? I have saved it for the second floor. From the position it is in it only illuminates one window, giving the illusion that there may be a wall between them, or perhaps someone working at a desk by candle light.

The final step, well done for making it this far! This is just a housekeeping thing really, I have glued the resistor and rats nest down so that they wont ever short together. I recommend doing this if you don't have insulation tape or heat shrink, or if you don't know what those things are...
Quick test once everything is in.
Battery pack squirrelled away, switch accessible - of course!
The final product!
I hope you made it this far and injury free, no less. This takes me about 45 minutes per building, with some down time waiting for soldering irons and hot glue guns to heat up. This can be applied to many different kinds of terrain limited only by your imagination and battery size! One of my next tutorials will deal with getting lights into smaller spaces and hiding away those batteries. Until next time!

No comments:

Post a Comment