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Datalogger and Mixed Analog and Digital Inputs

Discussion in 'Electronic Basics' started by TomM, Oct 2, 2005.

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  1. TomM

    TomM Guest

    I'd like to make a datalogger for several sensors. Most of the sensors
    are analog and I know I will need an A to D conversion. I have found
    out how to do that. However, one of the "Sensors" is an array of four
    swithches that can have a number of off/on settings.

    This is essentially digital data but I don't know how to capture it.
    Would I have to get the on/off value for and log it for each switch
    individually and later process it, or is there a way to get all of them
    and convert it to a four digit digital value.

    Plase bear with me, I'm new to this.

    Thanks in advance.
  2. Take the 4 digital inputs and feed them to a R-2R DAC and sense the
    output as an ANALOG signal. The output of the DAC will be unique for
    each possible combination of the digital inputs. You may need to
    provide a driver circuit if the digital data cannot power the DAC
  3. Rich Webb

    Rich Webb Guest

    Some idea of the scope (how many, how much $$, how much effort, how
    powered, how hot, how fast, how accurate, how soon, ...) would help.

    Without knowing any of that, the answers you get here are just guesses.

    With that in mind, if I were doing this I'd probably get one of the
    inexpensive USB gadgets from, either the
    miniLAB 1008 or the USB-1208LS, and hook it up to an old but still
    working laptop PC. A bit of PC-side software and you're done.

    If you want or need to roll your own, there are a ton of inexpensive
    microcontrollers with A/D and (of course) digital inputs. If you are
    using a PC to log the data, add some signal conditioning and you're
    almost done. Otherwise, stick on a cheap I2C flash/eeprom memory chip.

    Of course, if what you're logging needs 16-bit precision at 100 Msps
    and has to work through impact with a concrete wall at 600 kph, then
    the answers might be slightly different.
  4. Chris

    Chris Guest

    Hi, Tom. Please give more information:

    Are you looking for a do-it-yourself circuit, a kit, or a store bought

    Are the switch contacts available for you to hook up GND and some
    pullups? Or do the switches output a voltage? Is it AC or DC? What
    voltage levels are the ON/OFF settings?

    Does the switch voltage have to be isolated from GND? How about the
    analog voltages?

    How frequently do you need to log data?

    How many is "several" analog inputs?

    Is the analog input voltage AC, DC or both? What is the range of
    voltage to be read? Are overvoltages a possibility? How much noise is
    going to be superimposed on your analog input voltage?

    What kind of accuracy do you need on the analog inputs? One part in
    256, 1024, 4096, 65536? All of these are available, with progressively
    more cost as precision increases.

    You want datalogging to what? Do you want to buy something that has a
    chart recorder built in, are you putting this data in an Excel
    spreadsheet, or do you want to use this data to control something else?

    Is this data going to go to a PC? If so, are you anticipating writing
    a program to get or use the data? If so, what programming language are
    you using?

    How about the price/quality/service balance? Describe more about your
    project, so someone else can get a feel for whether you need a Yugo, a
    Chevy or a Cadillac.

    There are so many different good answers to your question, depending on
    how you define your project.

    Hope to hear from you again
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