[sdiy] Microchip PIC 5 x 4 matrix

[Vinicius Brazil]

Hi Jean-Pierre,
I did something similar but put a 10k pull down resistor on the "Rx In" due
to distances of the keys to the PIC.

Vinicius Brazil

On Wed, Oct 7, 2015 at 11:32 AM, Jean-Pierre Desrochers <jpdesroc at oricom.ca>
wrote:

> Hi Tom,
>
> The PIC has no internal pullups on port A.
> You were right. I uploaded a corrected picture
> on the same link shown.
> And yes the 100 ohms is for the LED's current limiting.
> The voltage drop of the led + the series diode gives around
> 2.2 + .7 = 2.9v leaving 2.1v (@ 5vdc) for the limiting resistor.
> At 20mA that gives around 100R.
> Thanks for your good reply (as usual).
> JP
>
>
>
> Le 2015-10-07 10:07, Tom Wiltshire a écrit :
>
>> 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
>>> _______________________________________________
>>> Synth-diy mailing list
>>> Synth-diy at dropmix.xs4all.nl
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>>>
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