sense if input is varying voltage? Not stable

Discussion in 'General Electronics Chat' started by elRey, Feb 28, 2009.

  1. elRey

    Thread Starter Active Member

    Feb 23, 2009
    65
    0
    Hello,

    What is the simplest way to sense if input (0.5V-4.9V) is constantly varying and not stable (stuck at any voltage between range). Maybe with a 2Hz - 5Hz sample rate?

    Thanks,
    Rey
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    I think your sampling idea is correct, assuming a microcontroller with ADC is in use.

    A reverse debouncing bit of code, sample and compare, if out of limits, do <whatever needs to be done if voltage isn't steady>

    Linear method would get a bit ugly, RC networks and comparators.
     
  3. umer27

    Member

    Feb 28, 2009
    25
    0
    well Ive recontly come across something like this as well ..

    I was using a reed sensor, and when I first counted the pulses with my micro controller , Got a different pulse count everytime.. so had to look at de-bouncing the switch.

    Ive come up with 3 solutions and Im not sure, which would the most suitable one to go with .. Your input is most welcome:

    Option 01:

    Using a RC filter , it works fine..Its simple, easy but can still cause problems under certain conditions..


    option 02:

    Using the read switch on the Low side, and basically using a schmitt triger , this has great results .. but adds hardware..

    Option 03:

    Software solution, this one works best , even when you dont have an adc available.. First you check if the signal is low, check again after a little while, if its still low, only then count it as low.. same for the high signal.. you can check as many times to increase the accuracy ..

    The project im working on needs a lot of accuracy, Its a solar tracker , and is designed to work for months without accumulating any errors, ... So, im thinking of doing the RC filter thing, then feeding it to the ADC .. It wont miss a single pulse ever ! .. (hopefully .. :) )
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    How are you planning to sense this voltage?

    Using a microcontroller or analog circuits?

    What is the frequency of the varying signal?
     
  5. LesterPhil

    Member

    Feb 25, 2009
    10
    0
    Didn't state here that you will going to use the sensing in your system or what so ever...
    for me, the way to sense that is... use oscilloscope....
     
  6. elRey

    Thread Starter Active Member

    Feb 23, 2009
    65
    0
    Sorry. More details..

    input signal is a randomly varying 0.5V-4.9V non-pulsed from a Manifold Absolute Pressure sensor (MAP).

    I need to make sure it varies or assume something is wrong (bad sensor/signal). If I detect the signal is stable at any voltage in the range I will then stop a PWM circuit around a 556 or 555.

    analog circuits, no microcontrollers

    The signal could stay in the 0.5V-1.5V range for extended periods of time. So I need to detect a relative change instead of an absolute change.

    Thanks,
    Rey
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    What ΔV/ΔT defines "Working ok" in your case?

    The same parameters that would cause a 'check engine' light to go on, or more strict?

    Is application for permanent installation or verification?
     
  8. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You can make a differentiator circuit by using an op amp to detect variations of the sensor voltage.
     
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