[sdiy] Microchip PIC 5 x 4 matrix

[Vinicius Brazil]

JP,
My key reference ON was the Vcc, like yours, and when a key was open, in
your case an RA, the pin was very noise, possibly interpreted as "1" (some
keys to 0.5 meters). With pull down the noise reduced considerably.

In the case of Key On being read RAX = 0, then Key Off = 1, pullup. In this
case reverse diodes and LED.

In your drawing, when Key Off, the pullup pull RAx to +5V, the ON condition.

VB

On Wed, Oct 7, 2015 at 11:57 AM, Jean-Pierre Desrochers <jpdesroc at oricom.ca>
wrote:

> Vinicius,
>
> Can you clarify what a difference pull down or pull up makes here ?
> Each final pin input impedance is the same here ?
> Unless you want all your wiring ground related.. (??)
> JP
>
>
> Le 2015-10-07 10:46, Vinicius Brazil a écrit :
>
> 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 [1]
>>
>> 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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>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy [2]
>>
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