[sdiy] Microchip PIC 5 x 4 matrix

[Jean-Pierre Desrochers]

Thanks for the explanation.
A pull down version like yours comes better.

Le 2015-10-07 11:15, Vinicius Brazil a écrit :

> 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] [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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> Links:
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> [1] http://www.arcenson.com/public/PIC16F88_5x4_matrix.JPG [1]
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[1] http://www.arcenson.com/public/PIC16F88_5x4_matrix.JPG
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