[sdiy] Microchip PIC 5 x 4 matrix

[Tom Wiltshire]

What does the 100R do? Is that a current limiting resistor for the LED?
What about pull-ups for the buttons? Does the 16F88 have internal pull-ups on Port A?

Aside from those questions, it looks fine to me, JP. Nice and simple.

Personally, I'd have done it with serial-parallel and parallel-serial chips, but that's because I've got code for that already. 74HC594/595 and 74HC166/165 can both be driven from 6 pins total (or even five if you use the same clock for both in and out), and you can extend the chain as long as you want.

Your way saves the six(!) other chips I'd have used though, so it's probably to be preferred.

Tom

On 7 Oct 2015, at 14:52, Jean-Pierre Desrochers <jpdesroc at oricom.ca> wrote:

> I'm about to build a MIDI foot controller
> using around 20 normally open footswitches
> with there respective state LEDs.
> I have a bunch of PIC16F88 micros and want
> to use one for this project using as less pins as possible.
> (9 pins for the matrix)
> I figured out a way to read and feed all switches
> and LEDs this way:
> 
> http://www.arcenson.com/public/PIC16F88_5x4_matrix.JPG
> 
> All the switches and LEDs will be processed one after each other
> in an endless loop..
> RB5 will send the MIDI data.
> 
> Does anybody see something I forgot in that drawing ?
> I'm not home and will try it tonight.
> 
> Thanks. JP
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