Underlight Your Dalek (or Other Project)

You know how it goes - you take you Dalek out and have a great day, but you get held up and when it's time to come come it's already dark. You try driving Alan (yes, the Dalek's name is Alan - don't ask me why) back but you keep scraping him on the pavement or getting him stuck in potholes because you can't see where he's going. If only there was a better way...

THERE IS! Give your Dalek some under-skirt lighting. Boy-racer that mother-exterminator to the max!

You will need:

• A Dalek (or other wooden project with similar skirt)
• LEDs (just a few LED lamps could do it, but why not give your Dalek some mood lighting?)
• A power supply (we use two car batteries in series... this could run a string of 12x 20mA red LEDs for 4 months)
• A soldering iron
• Solder
• A glue gun
• Glue sticks
• Wood
• A drill
• A saw
• Wires (speaker cable is massively over-specced for this but we happened to have loads lying around)
• Resistors of appropriate sizes
• Oodles and oodles of patience

Many of these things will be available at your local Makerspace, such as Southampton Makerspace, UK.

Your planning will differ from ours, so here's how we planned.

Power supply: 24 - 26V

Potential mounting points: 16

6 LED lamps @ 3.3V = 19.8V

8 regular LEDs @ 1.8V (red), 2.2V (green), 2.9V (blue) = 14.4V (red), 17.6V (green), 23.2V (blue)

So with the above we can 2 strings of each LED type for a total of 8 LED strings and 60 LEDs.

Our LED lamps want 350mA, we need to drop 6.2V (26V - 19.8V), so we need a resistor (V = I R; R = V / I) of 6.2V / 0.350A = 18 ohms. Beware: this resistor will be releasing about 2W of heat (P = I V = 0.350A * 6.2V = 2.17W), so a standard 1/4 W resistor will not be sufficient!

Other LEDs want 20mA, red: (26V - 14.4V) / 0.02A = 580 ohms, green: (26V - 17.6V) / 0.02A = 420 ohms, blue: (26V - 23.2V) / 0.02A = 140 ohms. (Standard 1/4 W resistors are fine for these.)

We were using 30mm strips and 10mm LEDs so we figured 4 10mm LEDs with 5mm between each and 15mm padding on both ends would work well; you may wish to experiment to find what works for you. You might also consider clustering the LEDs rather than mounting them in a line - it all depends on the constraints of your project.

I'm lazy so I just did this with a nail and a hammer. You want one guide hole in the middle of where each LED will go, and one in the middle of the two padding areas at the ends for the mounting screws to go through.

We drilled with a 6mm bit that's the perfect size for the screws we were using and sufficiently small that the LEDs would not fall through them (since we were using 10mm LEDs). If you are using smaller LEDs you'll want a smaller drill bit for the LED holes. You can use a hand drill or power drill if you like; but a pillar drill makes this so much easier!

Since we needed 16 LED mounting strips we found it easiest to do this with a band saw.

Be careful to maintain polarity (the longer LED leg is positive) - we used a red plus to signify the positive side. We bent the LED legs to keep the LEDs in the holes before we could glue them.

Before gluing it's a good idea to ensure that none of the LEDs accidentally went the wrong way around. I found the easiest way to do this was with a 3.0V lithium cell battery.

Place the negative (small) terminal on the negative LED leg, then bend the positive LED leg to touch the outside of the battery (which is positive). The LED should light. You can use this test even on 1.8V red LEDs without damaging them because the internal resistance of the battery prevents the LED from burning out.

This can take a log of glue, don't be stingy! Glue gun glue is generally insulating so you can use it instead of heat shrink - but be aware that you need to solder the legs later so leave enough uncontaminated!

This is a long and boring process - each LED requires two solder joints for a total of 120 solder joints. Be careful to maintain the polarity of your LED strings and to not cross the wires - using coloured wire (red for red LEDs, green for green, etc) can help greatly with this. For our Dalek we allowed between 300 and 400mm between each board for flexible mounting.

We used small spacers to prevent squashing the solder joints against the Dalek and screwed through into the Dalek base with 40mm wood screws.

Connect up your power supply and make sure everything lights exactly how you want it to. Don't forget to include the resistors you calculated earlier in your finished circuits otherwise you'll have a lot more soldering to do... And some LEDs to replace.

Now if only you had PWM control of the various light levels for some mood lighting... But that's a topic for another instructable