Tuesday, January 19, 2016

designed wiring harness

Planned LED lighting system for the astronomy case α primus. A little challenging with the clamshell lid, slider rails, and dual trays each side.

Going to put two LEDs inside each upper tray, facing backward. These trays lift up and slide/tilt back. I need to accommodate for this. In terms of wiring. Traces coming up from the middle of the both tray should work OK.

Going to put two LEDs on the front edges of the bottom of the upper trays. These to illuminate the lower tray.

Both of these sets, I need to accommodate for the pairs of trays sliding outward when opened and inward when closed. I tested this by temporarily fixing a wire to the bottom of the bottom tray and to the inside the lower bay. I tried the wire taped to the outer edge of the sliding drawers which worked fine. I just needed to tuck the wire inside the lower bay before closing the lid.

Now that I think about it, if the wire attaches to the bottom tray on the inner edge, then the wire will automatically pull inward when closing up. This would reduce the chance of catching on the lid...

And then, finally, I want to put two LEDs in each of the two lower bays. Once again, facing backwards.

Tried sketching the wiring harness, electronically. That was somewhat helpful. It highlighted that if the wiring emerges from the side of the main body two-thirds of the way back, it will be perfectly aligned underneath the front corner of the upper tray.

Made up an electrical diagram or schematic. Simple enough. It gave me an opportunity to optimise the wiring harness. If I keep the resistors near the LEDs and make key junctions or terminals at the edge of the case, I can have but two wires passing to the trays. My previous two LED lid designs had a resistor bank near the battery and switch. This would not work well in this case with the sliders and trays.

It also highlighted the parts needed.
  • 12 red LEDs, low-profile 
  • 12 resistors, low-ohm, ¼ or 1/8 watt
  • battery pack, AAx2 (with master switch, ideally)
  • tilt switch (optional)
I still have a few of the tiny, dome, low-profile LEDs left, never used. Just over a dozen. However I don't have a dozen low-ohm resistors—the 39 ohm bin is empty. I'll have to look around for a battery pack. And a little switch, if the battery pack does not had one on-board. I'm sure I have one tilt switch left.


I was in the back of my brain earlier. I wonder if I should bundle two LEDs to one resistor...


Right. Not possibly if I'm using a two-cell battery pack... Needs 4.5 volts or more.

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