[sdiy] Microchip PIC 5 x 4 matrix

[Jean-Pierre Desrochers]

> Let's not get crazy with series diode with LED, most LEDs will be OK 
> even at higher reverse >voltage.

The reason I put the series diode is that most LEDs specs states
around 100uA leak reverse current @ 5vdc so I make it safer with a 
series diode.

JP

Le 2015-10-07 16:28, Roman a écrit :

> The diodes shoud be reversed (RBx=0 at switch read then) or 10k should 
> be pull down and not pull up, otherwise you will not detect pressed 
> button.
> Let's not get crazy with series diode with LED, most LEDs will be OK 
> even at higher reverse voltage. And you can always go down with supply 
> voltage to be safer.
> If you want to drive 5 LEDs in a single row from one RBx pin pulled 
> low, that's about 15mA, and definitely RBx will not be at 0V anymore 
> then, but maybe 0.5V or more. That may result in varying brightness 
> depending how many LEDs are on in a row. 5 transistors will fix that. 
> That is irrelevant of course if you plan to light only one of 20 at a 
> time.
> 
> Roman
> 
> Dnia 7 października 2015 15:52 Jean-Pierre Desrochers 
> <jpdesroc at oricom.ca> napisał(a):
> 
>> 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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