Re: Effect of lengh of wires in matrix


roxlu wrote:
Luhan wrote:
roxlu wrote:
Hi,

I've created a small prototype where I connected 64 tiny dip-switches
in a matrix of 8x8. Using a
serial in shift register and a serial out shift register I'm scanning
through these buttons to check which one is pressed. This works
perfectly.

Now I'm gonna buy a lot more and bigger buttons (33mm, 256 pieces). The
matrix will be approximately 100cm x 100cm. As I'm not very experienced
in electronics I'm curious how this will afffect the workings of my
circuit.

I'm using a PIC16f628 for the scanning and I'm communication with a PC
using RS-232.


Sounds like a good design. My money is on it working just fine. There
is a built-in lag in reading via the shift registers.

Luhan


Luhan
But are those long wires to all those butttons (256) in a 100cm x 100cm
wooden plate gonna interfere my circuit in any way?

The shift register used for input should have 330 ohm pull-up resistors
to prevent noise pickup. The output shift register should then drive
one line low at a time.

You may also wish to 'debounce' the input by reading the input s/r
several times in a row for each change of the output s/r.

If your environment has a lot of electrical noise, put a grounded layer
of foil on the back of the wooden plate.

Good luck,
Luhan

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