Help: Arduino + MAX31855 (TC amplifier) + 4051 Multiplexer(s)

Discussion in 'General Electronics Chat' started by cmccoy21, Jun 10, 2014.

  1. cmccoy21

    Thread Starter New Member

    Jun 10, 2014
    1
    0
    Hello,

    I am trying to design a simple data collection system using thermocouples to take temperature measurements. To reduce costs of multiple thermocouple amplifiers, I intend to use a multiplexer to take in the multiple (8) thermocouples and feed into a single thermocouple amplifier.

    I'm fairly new to electronics, would like help to better understand how one would connect the 8:1 multiplexers to the MAX31855 and Arduino UNO.

    From my understanding, one multiplexer would take in the positive leads of the thermocouples and another multiplexer would take in the negative leads into the 8 analog inputs. Then the multiplexers each would send one analog output (one positive and one negative) to the terminal of the thermocouple amplifier which then connects to the arduino.

    But what about the select pins? Those connect to the arduino, right? (see here: http://playground.arduino.cc/Learning/4051)

    Here are the components:
    Arduino: https://www.adafruit.com/product/50
    Thermocouple Amplifier MAX31855: https://www.adafruit.com/products/269
    4051 Multiplexer: http://www.digikey.com/product-detail/en/CD74HC4051E/296-12810-5-ND/475938

    Thanks!

    PS. I have also seen/read of designs that have 8-channels (8 thermocouples) with a single multiplexer, although I have no clue on how that works... Hello,


    I am trying to design a simple data collection system using thermocouples to take temperature measurements. To reduce costs of multiple thermocouple amplifiers, I intend to use a multiplexer to take in the multiple (8) thermocouples and feed into a single thermocouple amplifier.



    I'm fairly new to electronics, would like help to better understand how one would connect the 8:1 multiplexers to the MAX31855 and Arduino UNO.


    From my understanding, one multiplexer would take in the positive leads of the thermocouples and another multiplexer would take in the negative leads into the 8 analog inputs. Then the multiplexers each would send one analog output (one positive and one negative) to the terminal of the thermocouple amplifier which then connects to the arduino.


    But what about the select pins? Those connect to the arduino, right? (see here: http://playground.arduino.cc/Learning/4051)


    Here are the components:
    Arduino: https://www.adafruit.com/product/50
    Thermocouple Amplifier MAX31855: https://www.adafruit.com/products/269

    4051 Multiplexer: http://www.digikey.com/product-detail/en/CD74HC4051E/296-12810-5-ND/475938



    Thanks!


    PS. I have also seen/read of designs that have 8-channels (8 thermocouples) with a single multiplexer, although I have no clue on how that works...
     
  2. crutschow

    Expert

    Mar 14, 2008
    14,802
    3,802
    The multiplexer has 3 inputs that are the binary address of the input that is active. Those go to 3 Arduino digital outputs. You program those in software to output the desired 3-bit binary address. Thus you read the channel, change to the next binary address, read the channel, etc., until you have read all 8 channels, then repeat. Note that it's likely a pause will be needed between changing the address and reading the value to allow time for the signal to settle to its new value.

    You could also use single 8-channel differential multiplexer, such as the CD4097 instead of two CD4051's.
     
  3. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,695
    555
    Yes, the select pins connect to arduino board. If I am reading datasheet right, 4051 has 3 select pins labeled S2, S1, S0. Makes sense that there are 3 of them, 2^3=8 for 8 channels. So on arduino board you will need 3 pins to select channel, 1 pin to turn the chip ON/OFF. That is how you control the chip, you activate the 3 pins to select which channel you want to be ON, then you activate the Enable pin to let the selected channel through.

    See Table 1 in the datasheet to see which S2-S1-S0 combination corresponds to which channel.
    000->Channel A0
    111->Channel A7
     
  4. bobalony

    New Member

    Apr 25, 2014
    8
    0
Loading...