[sdiy] Microchip PIC 5 x 4 matrix

[Jean-Pierre Desrochers]

> Minor criticisms are that the 100 ohm current-limiting resistor should 
> be on the LED path, >possibly instead of the extraneous diode, but not 
> the switch path.

You are right on that.
The drawing has been corrected.


Le 2015-10-07 15:03, rsdio at audiobanshee.com a écrit :
> I think you should be able to accomplish your project with the 
> PIC16F88.
> 
> However, my first reaction when seeing that circuit is that I don't
> understand how the button reading can work. Maybe I'm missing
> something, but with RBx OUT=1 and the 10k pull-up to +5vdc, there
> would be no difference whether the switch is open or closed.
> 
> Minor criticisms are that the 100 ohm current-limiting resistor should
> be on the LED path, possibly instead of the extraneous diode, but not
> the switch path.
> 
> 
> As for your project, you might want to consider LED brightness. With a
> 5 x 4 matrix, your maximum LED pulse width will be 1/5 or 1/4. You can
> get better duty cycle, and potentially simpler code, by arranging an 8
> x 3 matrix. Of course, that allows 24 buttons and LEDs, which is more
> than you need, but it also allows a pulse width of 1/3, which will be
> a little brighter for the same current. The PIC can handle 25 mA,
> which is more than most LEDs can handle at DC, but perhaps less than
> your LEDs can handle under PWM. Another disadvantage is that 8x3 takes
> two more GPIO pins (11) than 5x4 (9), but it might be worth squeezing
> things in. There should still be one spare GPIO for other uses. I'm
> assuming two pins for the crystal and two pins for MIDI I/O. You'd
> have a second spare GPIO if you don't implement MIDI In.
> 
> Another good chip to consider is the PIC18F24K50, in my opinion, but
> you already have the PIC16F88.
> 
> Brian
> 
> 
> 
> On Oct 7, 2015, at 6:52 AM, 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.