Force sensor help

rr

Hello,
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I have a force sensor that·I am trying to use in a project. It is basically just a variable resistor, when you touch it lightly it measures about 1M Ohms and as you press harder it goes all the way down to about 1K Ohms. What is the best way to get data from this sensor into my stamp (OEM BS2)?·I tried an RC time circuit with a .01 cap and it seems like it doesn’t measure well. One of the problems is that the data received·is more than a Word variable can handle. Anyone got any ideas how to do this right.
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Thanks for the help.
rr
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sdy

Use an A/D to measure a voltage drop across it.

Phil Pilgrim (PhiPi)

RCTIME is more than adequate for such a task. I tried it myself with a similar force sensor (>2M max resistance), and it works fine. The trick is to put a 100K resistor in parallel with the sensor leads, as the attached schematic shows. Here's the code I used to test it:

' {$STAMP BS2}
' {$PBASIC 2.5}

io    PIN 0

value VAR Word

DO
  HIGH io
  PAUSE 7
  RCTIME io, 1, value
  DEBUG DEC value, CR
LOOP

It's relatively insensitive to an extremely light touch, though. If you need that extra sensitivity, you can use a higher-value parallel resistor and a smaller cap to keep your values in range.

-Phil