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Multiplexing an A/D convertor

Discussion in 'Electronic Basics' started by Dennis Dunn, Apr 14, 2004.

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  1. Dennis Dunn

    Dennis Dunn Guest

    Hello,

    I would like to connect 1 of n sensors to an A/D convertor. The idea is
    to have a microcontroller select one of the n sensors and then have the
    A/D do it's thing and then move onto the next sensor. The thing that I'm
    not sure of ... rather make that "one of the things" ... is how do I
    switch the input of the A/D chip to the ouput of the various sensors?

    If the sensors provided digital signals it would be a simple matter but
    the output of the sensors are voltages that vary from 0V to 5V. The two
    devices I am using are an absolute barometric pressure sensor and an
    accelerometer, in the future I would like to add two more accelerometers.

    I would appreciate any clues as to what I need to look into next.

    Thanks for your time.

    --dennis
     
  2. CFoley1064

    CFoley1064 Guest

    Subject: Multiplexing an A/D convertor
    Look into the 4066 CMOS quad analog switch. It gives you four bilateral
    switches, and you can set it up quite easily so it will switch one of the four
    sensors to your A to D input (view in fixed font, or M$ Notepad):

    Analog Multiplexing With a 4066
    .-------.
    | |
    Ain(1)o---------o 4066 o-------o-------------o uC A-D Input
    | | |
    | | |
    '---o---' |
    | |
    '-----------|-------------o Sel 1
    .-------. |
    | | |
    Ain(2)o---------o 4066 o-------o
    | | |
    | | |
    '---o---' |
    | |
    '-----------|-------------o Sel 2
    .-------. |
    | | |
    Ain(3)o---------o 4066 o-------o
    | | |
    | | |
    '---o---' |
    |-----------|-------------o Sel 3
    .-------. |
    | | |
    Ain(4)o---------o 4066 o-------'
    | |
    | |
    '---o---'
    |
    '-------------------------o Sel 4



    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    This setup's a bit of an I/O hog, because you need 4 uC pins to select one of
    the four switches, but you can do it with one chip. There are other ICs that
    will do the job, too. Some have 1-of-n decoders built in, and other features.
    Look around -- you'll be amazed how many different ways there are to skin this
    particular cat.

    http://www.onsemi.com/pub/Collateral/MC14066B-D.PDF

    Good luck
    Chris
     
  3. Thats correct, so why not suggest the analogue multiplexer right of the
    bat, say the 4051?

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  4. Gareth

    Gareth Guest

    If you want to use one ADC with four sensors why not use a four (or
    more) channel ADC. There are lots of these available from the usual ADC
    manufacturers:

    www.analog.com

    www.maxim-ic.com

    www.ti.com

    www.linear.com

    You can also get microcontrollers with multichannel ADCs built in,
    though possibly not the one you want to use.

    Gareth

    --
     
  5. Rich Grise

    Rich Grise Guest

    Probably the same reason I didn't - we were waiting for somebody who
    remembered the part number to chime in. :)

    Cheers!
    Rich
     
  6. Dennis Dunn

    Dennis Dunn Guest

    Hello again!

    Thanks for all of your suggestions, next stop is the Digi-Key catalog!
    I didn't know there was such a thing as a quad-analog switch although it
    doesn't surprise me. This is the 21st century, after all. :)

    I was going to start learning about uC programming using Microchips PIC
    starter kit. I figured that $40 was a cheap investment to help ensure
    success in the beginning. Do you have any comments or suggestions?

    Thanks again.

    --dennis
     
  7. I use the 4051. With 3 digital lines you can select 8 analog channels.
    going into a CS5501 type 16bit ADC .
    Downside, you have to let the port settle between reads but that may be
    true for multi channel ADCs too.
     
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