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Ac signal to microC

  1. Mar 30, 2012 #1
    1. The problem statement, all variables and given/known data
    how can i transmit ac signal to μC to further ADC?


    2. Relevant equations



    3. The attempt at a solution
    can i use dc offset?
     
  2. jcsd
  3. Mar 30, 2012 #2

    berkeman

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    Staff: Mentor

    If I understand your question, yes. You can add a DC offset equal to half the expected peak-to-peak AC voltage (Vpp) to effectively convert it to a mono-polar time varying signal that a standard ADC could deal with.
     
  4. Mar 30, 2012 #3
    be aware that uC ADC conversion times can be slow, you may want to consider a stand alone IC
     
  5. Mar 30, 2012 #4
    what is stand alone IC?
     
  6. Mar 30, 2012 #5

    berkeman

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    Staff: Mentor

    He is referring to the A/D converter functionality. That can either be an integrated part of the microcontroller (uC) chip, or it could be a separate ADC chip. I think he is saying that ADCs on typical uCs have limited performance, so you might consider using an external/separate ADC chip, which you would interface to your uC via the IO lines of the uC (either using I2C or SPI serial protocols, or some parallel interface protocol).
     
  7. Mar 30, 2012 #6
    i see. if i use dc offset, is the output voltage ll become varies in ADC?or i need ac to dc converter is better?
     
  8. Mar 31, 2012 #7
    thankyou berkeman that is what i meant.

    phyky, your application here is quite vague, and the best solution depends on things you havent told us. any adc, a built in peripheral of a uController or a seperate IC will be limited by the maximum samples per second. for example, dsPic33F4013 has a maximum of 200 ksps.

    if you want to measure an ac signal of frequency 20kHz, you will only get 10 samples per cycle, which is enough to estimate the frequency and peak amplitude, but not enough to analyse distortion or check for harmonic content.

    if on the other hand you want to measure 100kHz, its not enough to do anything but check that the signal is there, and possibly measure frequency within a failry large error margin. you will find it very difficult to measure the peak amplitude, and impossible to distinguish between a square wave and a sine wave without some other knowledge of the signal.

    you also have to consider resolution, which may or may not affect you depending on what you wish to measure.
     
  9. Apr 1, 2012 #8
    i m doing computer interfacing. the microC connect to my computer.it is a built in microC with 10 bit ADC module.
    - Auto-acquisition capability
    - Conversion available during Sleep
    - Internal 1.024V Fixed Voltage Reference (FVR) channel
    - Independent input multiplexing
    so i need convert the ac to dc?
     
  10. Apr 1, 2012 #9
    its highly likely yes.
    look in the microcontrollers datasheet, it will should you the ranges that the adc can convert
     
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