9th December 2013
With the saucer lighting completed and closed up I decided to get back to the nacelle engine lighting.
For the nacelle lighting I’m making an array of 16 LEDs which will flash/chase to simulate the motorised lighting assembly in the original model Enterprise.
The inner 4 LEDs will blink randomly. The Outer ring (chasers) will light up in sets of 3 similar colours and will ‘rotate’ around the disk. So for the outer LEDs all the yellows will be lit, then all the reds, then all the greens, then all the blues. Rinse and repeat.
16 LEDs gives us 32 wires to deal with, so the best thing we can do at this stage is tap into all our reserves of abject laziness and see about reducing the wire count (less work to do and fewer wires to route through the ship later).
LEDs have a positive electrode and a negative electrode (Anode and cathode in LED jive speak). The good news is that to save on wiring and time we can just connect all of the cathodes together and run them from a single negative (or ground) wire.
To make this easier for this build I arranged the LEDs so that all of the cathode legs were on the same circle:
Here’s a Photo-shopped picture to (hopefully) illustrate the idea:
In the above rear view of the LED array, the legs on the LEDs are all aligned to point to the centre of the circle… I’ve drawn green lines that shows the alignment of the LED legs.
The anodes (positive electrodes) all lie on the blue circles, the cathodes (negative electrodes) all lie on the red circles.
Sorry for the clarity of the photo BTW – I’ve had a bit of a mare with photography this evening. First my usual phone camera packed up, so I fired up the DSLR which ran out of batteries and I ended up using the faithful (but senile) Ixus 50. The above photo was taken with the DSLR but trying to get clear photos of things that are silver, shiny, see-through and small seems to be beyond me lol 😉
Anyway, given that the legs of the LEDs are arranged in a cunning pattern, the first job to do in wiring them up was to nip off all the anode legs of the outer ring leaving about 5mm protruding…
With that done, the ring of cathode legs were bent 90 degrees to the right at about the same height that the anodes were trimmed off at…
Again, sorry if the photos aren’t that clear, damned shiny-see-through-chrominess :-$
And here’s another shot this time from the side that hopefully shows it more clearly… (The middle LED anode legs are still intact at this stage)
With all of the cathodes pretty much touching each other in a ring around the disk, they could be liberally soldered together… (Or conservatively or using labour depending on how you vote).
So in the above photo, everything in the solder ring is a cathode (negative leg) and everything else is an anode…
However, the wiring economy was not over by this point, we’d eliminated 15 wires by ‘commoning’ the grounds together, but I also wanted to reduce the number of positive wires (anodes) going to the microcontroller. For this each similar group of colours in the outer ring of LEDs are also commoned together. So all the outer yellows are connected to the same wire, all the same outer reds, all the same outer greens etc… This means that instead of 3 yellow chaser LEDs requiring 3 wires, they can all be driven from a single wire that connect to all three inside the nacelle.
Note that for this build I’m placing the required LED current limiting LEDs inside the base of the model and not close to the LEDs. Usually you’d wire this with one current limiting resistor per LED and mount them on the LED but for wiring and microcontroller channel economy I’m doing things a bit differently here…
Time to prepare the wiring. For any job like this it’s best to cut all the wiring lengths together in advance. That way you get a neater end result than just cutting wires as you go.
It’s also time for the wiring schedule to come out again to make sure I’m numbering the wires correctly so they can be hooked up properly later.
Confession/disclaimer/crap attempt at hypnosis: In the above photo you can see a single red wire connected to the LED array. Now I’d like to ask you to pretend that this is a black wire and not a red wire (look into my eyes, not around the eyes but into them…). The red wire above is actually my ground wire which by tradition (and good practice) should be black, however all I had in my stash was red and green and the red is slightly heavier gauge than the green – hence I decided to use the electrically better (thicker) wire for ground and not one of the correct colour. I’ve caused myself all kinds of pain when I have to connect a red wire to a negative terminal (mental pain not electric shock) but I’d highly recommend when you wire things to choose the traditional colours instead of my half baked scheme 😉
3,2,1 – you’re back in the room…
For this wiring scheme I’m going to need to daisy-chain from one LED to another. For this it is always best to use a ‘mechanical joint’ for the wiring by twisting it together before you tin it and solder it. This is where we want to have two wires soldered onto one pin, and the use of a mechanical joint allows you to solder the wires onto a single pin without them pinging apart and flicking solder in you eye.
Note: If you want to go totally “Isombard Kingdom Brunel” over the wiring job, you’d actually wrap the first wire around the second, and then wrap the second wire around its destination pin. Kind of a mechanical joint which then forms a mechanical joint.
Here’s one of the LED chaser wires soldered up and ready for attachment to the LED array…
The single end on the left will go to the microcontroller (via a resistor) the three daisy chained ends on the right will each go to an LED (yellow in this case).
Once all the wires were prepped as above, they were soldered onto the anode pins of the LEDs.
And here’s the finished engine nacelle lighting loom looking in all it’s glory like the optic nerve of a Terminator…
So there we go, 32 LED pins handled with just 9 wires running to the microcontroller.
Next job will be hooking this up to the microcontroller and writing some code to chase and flash the LEDs – gotta say it’s going to get pretty freakin Christmassy looking on my workbench