External Christmas Lights

You can buy external Christmas lights from any DIY or hardware store, so why make your own?

  1. Well, we were looking for some that were better made than the lights we had bought before. Most of the so-called external lights are not well protected from the weather and the metal used in the legs of LEDs will rust through in a few years of use, if they are subjected to a typical English winter.
  2. We wanted white, random flashing LED lights and not lights that run through a sequence or flash in groups. We were after a truly random twinkle and simple couldn't find any lights like this in the UK shops.
  3. We wanted lights that used LEDs for reliability and because they consume very little power. LEDs use ~20mA per LED but when flashing this is considerably reduced. The string of lights shown below use a 3V power supply at an average current of about 50mA, once the lights have settled into a truly random flash, which means they can be powered using 2 AA batteries for a long period of time.

Research

It's fair to say that this is not the first set of lights like this that we have built. This project captures the learning from a number of previous attempts.

Design

PVC tubing
To make the lights truly weather proof, they are encapsulated in transparent PVC tubing. The tubing has to be stable to sunlight exposure (it won't go opaque) and has an internal diameter of 8mm. You don't want to go any smaller than this. You have to somehow thread your lights down the inside of this tube. More on this later.

The length of tubing required depends on how long you want you string of lights to be. This determines the amount of wire you need and the number of LEDs required. I bought a 30m roll on eBay but expect about 20m to be used on this project.

The first thing to do is find a long reel of wire and double it up so that you can make a twisted pair. For this 20m long run I used about 60m of wire. You double it up to make a pair 30m long. You then fix one end and walk to the other, with a cordless electric drill in hand. Having fixed the ends of the wire in the drill chuck, power it up to twist the wire evenly along its length. As you do this, it gets shorter, with the 30m pair of wires ending up nearer to 25m in length. Don't over do the twisting because you need to undo some of it later. Once you are happy that you have a nice even twisted pair, then give it a gently tug to 'set' the twists.

If you want to simplify the process of soldering the LEDs to the wire later you can use two reels of different colour wire but this is not essential, as you will see.

LEDs
I bought my LEDS on eBay from a Hong Kong seller. They must be 3mm LEDs and you can get various colours and flashing sequences. I've used ones that flash in a sequence of colours before but, these are simple white, flashing ones.

Tools
Having the right tools makes the rather tedious task of soldering them all onto the wire so much simpler and quicker. You obviously need a decent soldering iron and solder. Some 'helping hands' also make things much easier whilst you solder. I bought mine from Maplin. You also need some wire strippers and cutters.

Wire separation
Having carefully formed the twisted wire pair, you now carefully undo this hard work, to fix the LEDs onto the wire :-( The main reason for taking this approach is that you don't want to cut the wires, as this makes them weaker and creates many new points of failure. All of the LEDs are going to wired up in parallel and obviously, one wire is positive and the other negative. The space between the LEDs is up to you but, a spacing of 25cm works well for us.

LED soldering
Because my positive and negative wires are both the same colour, we had to check which way the LED needed to go by touching the legs onto the wires. I used to AA batteries (providing 3V dc) to power the lights whilst I soldered them up. The LEDs will not be damaged by connecting them the wrong way round (they won't light up) and the batteries don't mind being shorted out for brief periods either.

LED soldering

Fixing the LED to the wires involves wrapping it round the legs and then soldering. As you can see, we cut the legs short before doing this as they are simply too long otherwise. As you can see from this picture, the two legs could touch together and short out.

LED soldering
To stop the legs and wires shorting, electrical tape is placed between the legs and wrapped tight around them. Make sure this is nice and tight, as this all has to pass down inside the tubing nice and easily. Any sharp edges will catch on the way down the inside of the tubing.

Rolled up lights
As we worked our way along the wire adding the LEDs, we wrapped the completed part around a suitable object to stop it all getting twisted up. This length took about two hours to complete and by doing the whole thing with battery power applied, it was tested as we went along.

Having got this far, the fun really starts! There is no way you can push the wire down inside the PVC tubing. From our previous experiments and research, the only way to achieve this is to use a reel of cotton and a vacuum cleaner. The following steps worked for us:

  1. Lay the tubing out on the ground in a dead straight line. Ideally you need two people to do these next stages as the the whole process is a lot easier if the tube is under slight tension.
  2. On the end of the reel of cotton, add a small ball of paper about 5-6mm in diameter. It needs to be able to pass easily down the inside of the PVC tubing.
  3. Attached a vacuum cleaner to the other end of the tubing and seal it well with tape to form an air-tight join. The plan is to then switch on the vacuum cleaner and suck the ball of paper down the tubing to the vacuum cleaner end. You will need to gently feed the cotton in at the far end. Now you can see why you need two people!
  4. When the cotton has reached the far end, don't even try to use this to pull the wires back down through the tubing! It will snap. Instead, use the cotton to pull some decent gauge fishing line or kite string back down the inside of the tubing. You can then use this to pull the wires through.
  5. Go gently as you pull the wires through. On a long length of tubing there is still quite a bit of friction to overcome.

Within the tubing, it is advisable to fix both ends of the wires using silicon sealant. This will also seal the tube ends and prevent moisture entering. Any excess wire from can be used to run to the power supply. You may need to add some longer wires to get power to the lights, depending on where you plan to install them. We have used them in a tree and on the house itself.

Status

Finished lights
These lights will be up in time for this Christmas :-) I will add a video here soon, to show the effect achieved. The randomness of the lights is truly spectacular and well worth the effort alone. They really do twinkle, rather than sequence.

And this is what they look like when powered on:

Conclusions

  • To some, it might seem like a lot of effort but, we think the end result justifies the work required. The lights are waterproof and very reliable. No more corrosion and untangling or failed bulbs! These lights are also incredibly energy efficient, using less than 1W of power.
  • One thing to note is that when you first power up the lights, they all start flashing on and off at the same time. It can take over 3 minutes for the flashing to get truly out of sequence and random, as each LED flashes at a slightly different rate.
  • Although these lights can be powered by batteries, we use an LM317 voltage regulator to provide a 3Vdc power source from a 12V battery. You need a decent heatsink on the voltage regulator.
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