ADC resolution

Discussion in 'General Electronics Chat' started by kppp, Mar 29, 2011.

  1. kppp

    Thread Starter Member

    Apr 23, 2008
    hello all,
    i am using PIC12F675 ic for ADC operation. Vref=5V resolution = 2^10 = 1023
    when i give input from 0V to 5V it works fine with 1023 resolution.
    i.e at the output 0V corresponds to 0V and 5V corresponds to 60V (on display)
    but now i have input from 0V to 3V which i want to show as 0V to 60V on LCD.
    i have calculation as: input Voltage ADC count * 60V / 1023 (it gives me 60V output at 5V input) ADC count at 5V = 3F0H
    but when i want to show 60Voutput for 3V input, i have 2 ways to do:
    1. reduce Vref to 3V which is not possible in hardware
    2.reduce resolution to 614 (for Vref=3V) so formula becomes
    input Voltage ADC count * 60V / 614
    ADC count at 3V = 25BH
    but is it a correct method?
    pls suggest me the solution.
    thank you all
  2. JDT

    Well-Known Member

    Feb 12, 2009
    What about an amplifier on the input with a gain of 5/3?
  3. Markd77

    Senior Member

    Sep 7, 2009
    A couple of other possibilities:
    You can use a Vref on the GP1 pin - unless you are using all the pins already
    You could power the PIC from a 3.3V regulator - unless it needs 5V for some other reason.
    The op amp is an option but it needs to be rail to rail capable (unless you have a higher voltage available to power it) and it has to be accurate otherwise you lose the advantage.
  4. uchugdx

    New Member

    Mar 31, 2011
    Hello Kppp,

    You might want to use OPA835 from TI to drive the ADC in the microcontroller.

    This part is currently sampling.

    Here is the link for that

    Please note that TI has a very wide portfolio of precision as well as high speed amps that work very well with such microcontrollers

    Also, we have e2e community on which you can post your questions and our system/apps engineer would address right away

    Thank you
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    What resolution do you need? That the real first question.