Analog to Digital converter with switch...

Discussion in 'The Projects Forum' started by monalith, Jun 4, 2014.

  1. monalith

    Thread Starter New Member

    Jun 4, 2014
    Hello Friends,

    This is my first post so first I want to say hello to everyone...

    My name is Eren and I am an MSC Mechanical Engineer working at testing engineering.

    Electronics is one of my hobbies but never designed my own circuits, only prepared some circuits from schematics.

    It is time to step forward and solve my own problem now...

    So the circuit I need has to read current from 40 different resistances.

    It does not need to be continuous and high sampling rate but needs to get the current values from 40 points and index and send to computer.

    I do not want to use a 40 channel analog to digital converter instead I want to use an electronic switch and a 4 channel analog to digital converter, so that I can index the channel and read the current value. So sampling rate will be very low but who needs sampling rate for constant current values anyways :)

    Any suggestions ???

    Thank you for sharing your experience and ideas.
  2. crutschow


    Mar 14, 2008
    Hello Eren,
    Welcome to the forum. :)

    Here's an inexpensive 10-bit 240 samples/sec 4-channel analog converter that has a USB interface. Three 16-channel analog muxes (switches) could connect the 40 signals to 3 of the analog inputs.

    A suitable 16-channel mux would be a CD4067. You would need to add some timing circuits and a clock to sequence through the 16-channels and send a sync signal through the digital inputs to the computer.

    A typical sequence would be:
    1) Set muxes to the first channels
    2) Read the three mux signals with the converter
    3) Increment the address of the three muxes
    4) Repeat 2 and 3 until all signals have been read.
    5) Repeat 1 through 4.
    Last edited: Jun 5, 2014
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
    Hm. 64 inputs ADC from TI is 140 USD, probably a little more in Europe (or not). From what you said, it looks like you already seen that price tag.
  4. alexfreed


    Oct 8, 2012
    Probably the easiest way to do it is to use a microcontroller with built in ADC. They all have internal analog switches so that there are more than a single ADC input pin, but not 40. So you have to add external multiplexers. You write that you need to read current but from resistors. So I assume you are actually measuring voltage across resistors to calculate the current. Are the resistors grounded? If not, you may need to use differential inputs to the ADC.
  5. crutschow


    Mar 14, 2008
    For that you would likely want a μC with a USB interface so the op can send the measurements into a computer as he wants.
    Last edited: Jun 5, 2014