Monday, 5 May 2014

LED Desk Light – 4 x 5 Matrix – PCB – Part 1

Now that I have completed the perf-board prototype of the 4 x 5 LED matrix, it’s time to start work on the printed circuit board version.
I’ve laid the board out, pretty much the same as for the perf-board version, although I want to try something slightly different with the positive and negative traces so that I don’t have to use any jumper leads to do the column joins.
The new layout is below
Fritzing 5 x 4 LED Array_etch_copper_bottom_mirror_thumb[1]
The above is the bottom layout in mirror reverse. You can see that all of the positive traces connect at the bottom of the columns and the negative traces connect at the top. It’s no longer simply a bent parallel line of LED, but an integrated parallel circuit. I think that this layout will work, theoretically, but I’m not sure if it will, practically. Note the missing trace in the middle of the board!
I also found out that I can make Fritzing lay out the resistors in a horizontal alignment by changing the pin spacing … simple, really, and something the Fritzing team already though of.
Fritzing Resistor_thumb[1]
This makes the Fritzing layout very similar to the perf-board layout.
I’ve printed the bottom layer out and transferred it to my single layer F4 copper clad board.
The transfer is OK
Picture 33_thumb[1]
although it is a little bit … bitty. I still need to print this out on some decent paper. However, with the traces “mostly” there, I can go over the circuit with my trusty permanent marker.
Picture 37_thumb[1]
Using a ruler and reading glasses, it becomes better.
The pads are probably a little bit blobby, but that’s OK too. This is still just a prototype. I think I need a finer permanent marker … or better eyes.
From here, I’m going to etch the board. But that’s a job for tomorrow night.

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