Friday, 19 July 2019

KiCad Kata

Pretty (but dumb) LED Matrix
The picture shows the result of another workout with KiCad as executed by Seeed Studio and finished by me. This looks rather prettier than the original and was considerably easier to solder, not to mention more LEDs!

However a few defects are obvious too:

  • the LED spacing is wider than on stripboard, which can make patterns harder to discern
  • the interface split between anodes and cathodes is the same as the original, for no good reason
  • it now uses 16 gpios!
The first and second of these are my fault but the last could have been mitigated by adding an LED driver, such as the MAX7221 to the design:
MAX7221 DIP package
This particular chip requires only a couple of capacitors and a single resistor to function (see the circuit here). Also it is cheap, less than €1 from China and has a mature Arduino library. It could comfortably have fit in the space occupied by the resistors on the left of the picture. On the downside, it requires a 5v supply. (The Arduino playground has a lot of information about it.)

So, it was instructive to lay out an LED matrix and write a library for it, and I'd encourage you to try it for yourself. (However I also won't blame you for simply buying one on eBay, they seem to be cheaper than the cost of parts somehow!)

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