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scaling resistances for ain


ultra

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i'm planning on using a resistive touchscreen that only has a small amount of resistance, and i'd like to scale this to work with ain.  i'm not too familiar with the ain module, but i guess it reads voltages and i would like to use a device that can output the voltage to the ain based on what is fed into it by the touchscreen.

the resistance ranges are:

top to bottom: 120 min 300 max

left to right: 580 min 900 max

these work on a range of 3 to 12 volts, so using 5 should be ok.

i'm not sure if this even comes into play, but the contact bounce is 5 ms minimum and 10 ms maximum.

can someone please point me in the right direction?  thanks.

ultra

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i think i figured out what to do, and it's pretty simple.

i'll use a voltage inverter schematic i posted a while back for those bgmicro lcds (http://www.sub-version.net/images/negativeconversion.gif).  one side will get -5v, one will get +5v, and i'll make a divider between the two using the touchpad and a trimmer set to get 0v between them when the touchpad isn't pressed.  then i'll get a voltage when the resistance is increased and put that to the ain.  this would only give me up to about 3.5v for the y axis, and about 3v for the x axis, but i guess AIN has a pretty high resolution and for a 128x64 lcd, that should be enough. at highest resolution, i'll need values of 0-127 for using this as an x/y controller.  from here i'll just have to scale it in the software.

cimo your idea i'll probably try on my next parts order.  i can't say i totally understand it, but i'm sure i can play around with the parts if i have them.

bugfight, i picked up a lm324 but i really don't understand op-amps.  i read about them, but i can't see how it applies to this.  do you know of a schematic anywhere?

thanks,

ultra

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