High precision digital variable resistance

Discussion in 'General Electronics Chat' started by Inkwaterman, Jan 5, 2005.

  1. Inkwaterman

    Thread Starter New Member

    Oct 11, 2004
    6
    0
    Hi to everybody !

    I need to change the gain on a instrumental amplifier from a microcontroller.
    I used an INA118 and a PIC's family micrcontroller.

    For change the gain I must change the value of one resistance.

    Somebody know a High precision variable resistance usable from a PIC ?


    Thx

    :)
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Do you have some maximum value in mind? That would be for the minimum gain fugure desired.
     
  3. Inkwaterman

    Thread Starter New Member

    Oct 11, 2004
    6
    0

    Actually We don't have an idea about the gain.

    For now we are interested in the scheme of electronic circuit, above all in the programmable resistor.
    I have seen some data sheet of variable resistor but the value of tollerance usually is too high, for a good programmable amplifer.

    Did you use some programmable resistance ?

    thanks
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Both Dallas Semi and Maxim make digitally controlled pots. Without any idea of values or tolerance, I can't suggest any particular one.

    For very precise values, consider using individual resistors, and either relays or FETs to switch them in and out of circuit.
     
  5. garocco

    New Member

    Oct 31, 2006
    1
    0
    I think you should be consider to use a resistor array with high precision resistances and select them with an analog switch (see some from Texas, Dallas or Maxim...). Or even better... there are instrumentation amplifier with digitally programmable gain (see Texas Instruments web page). But you need first to define the band width and how many steps of gain you need to get (and of course the max gain)...
    Some of this operational can vary its gain in steps of 1-10-100 and 1000. Others have steps of 1-2-4 and 8... but the band width is about a few kilohertz...
     
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