Help needed: =FSR pressure sensor resistance=

Discussion in 'General Electronics Chat' started by TomTommer, Mar 16, 2008.

  1. TomTommer

    Thread Starter New Member

    Mar 16, 2008
    Hello all,

    Maybe someone more experienced in electronics can help me with (I suppose) a newbie problem...

    I'm including a FSR pressure sensor in a circuit as a variable resistor.
    The problem is that FSR resistance doesn't go below approx. 5K at the maximum pressure that will be applied (it's inverse logarithmic?).
    Ideally, I need the resistance to gradually go to zero, but maintaining the characteristic of the sensor. So in a force-resistance graph, the graph is shifted to down, if that makes sense.

    Can anyone suggest a circuit I can use?
    Thanks a lot in advance.
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Going over the FSR material (the PDF file that loads off the home page), that's as good as it gets. I would direct you attention to the statements on page 8. It is not meant to be a precision device.

    Ordinarily, it could go into a resistive divider, and have an op amp with an offset voltage applied make the sensor signal go to zero. But the notice of variance of up to +/- 25% makes that a bit iffy.

    Do some experimenting. See how reproducible the output is over many trials. If it's closer to the best-case +/- 5%, then the op amp and offset voltage may get you there.
  3. TomTommer

    Thread Starter New Member

    Mar 16, 2008
    Hi Beenthere,

    thanks for the help.
    The sensor doesn't have to be very precise, it's used as a control.
    But it does have to go down to (almost) 0 resistance.

    I was thinking of using an opamp, but don't know how to go about it exactly.
    Any advice on components/circuit?

    Thanks again, really much appreciated.
  4. SgtWookie


    Jul 17, 2007