Weird multiplexing project

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I am working on a project where I will have to make an array of 32 resistive heating elements. The elements will be controlled by MOSFET, or maybe SCRs, I'm not sure which is more favorable. Whatever the gate is, it needs to either control the heat of the elements using PWM, or if a MOSFET, I suppose it could be controlled by variable voltage at the gate.

Corresponding to each of these elements is a force sensor, that will send a HIGH signal when struck. Each of these sensors needs to be calibrated with a digital pot.

That is 32 pins in, and 64 messages to go out.

This is a large project, and I have a couple of months to work on it. I am unsure of a few things:

What is a suitable chip to scan over all the inputs, and send the different types of messages out? I have been looking at the MCP23S17 port expander to receive the HIGHs from the force sensors, but how to send messages to 32 RDACs, or even 64 if using MOSFETs, is a more complicated question. Can that many digital pots be addressed and strung together?

I am sure there are many ways to go about this, but does anyone have some recommendations?

Thanks!

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Excellent questions:

The hits are punching, but once a strike is detected, the program takes over for about 2 minutes or so, and no more hits register. The force sensor is piezo element filtered and amplified, then run into a comparator.

The heating elements are warming thermochromic ink for the course of those two minutes or so. I figure that the elements should probably be "preheated", that is, running low amounts of current constantly, so that they can provide the temperature increase at a reasonable speed. A slow effect is desirable though, as it is simulating a sort of bruise forming on the fabric.

The source of power is from mains, no batteries necessary. I am trying to better figure out the power supply. My heating element is ripped out of an electric blanket that runs on 24 AC, but it's just teflon coated wire.

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I'd be happy to work with discrete components, but the catch is that the data from all sensors needs to be collected and shipped off, which makes things more difficult.