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Help with my new "rig"

  1. Aug 30, 2014 #1
    Hi Guys,

    i am going back to uni next year or at some point but am currently developing programming and experimental methodology at home until i feel im way ahead of things.

    Before even conducting any experiments i am building a main interface that houses the micro controllers which will be connected to a pc that runs an oscilloscope via the analog inputs of the MCs writing to the serial ports for the C programs ive write to display the real time voltage of each.

    I have built a sort of switch board which ive designed to be separated into 4 groups
    HIGH1 (OUTPUT > 400 v)
    HIGH2 (240- 120 V OUTPUT)
    LOW1 (80 - 40 V)
    LOW2 ( < 24 V )

    My plan is to connect these 4 to separate inverter circuitry systems that step down the output voltage coming from each of the "experiment subject output" to less than 9 V so to be safely connected to the micro controller input pins and i can then program their serial data logging code to scale the output data up by the corresponding factor for which each channel has been stepped down in voltage for the purpose of measurement, hence giving me the value of the output voltage of that my 'arbitary test subject' is producing at the other end of the line.

    As you might have guessed, i want this kind of setup as to have a systematic way of observing and recording electrical properties of things i build from the one interface systematically, as just building measurement apparatus on the fly is rapidly turning the workshop into complete disarray, where by it becomes difficult to move about in there!

    Basically my question is, is it realistic to expect accurate results from this kind of indirect measurement and if not what would be the voltage limit for which it will be to erroneous.
    Last edited: Aug 30, 2014
  2. jcsd
  3. Aug 30, 2014 #2
    I'd suggest just buying an oscilloscope. That microcontroller -> serial bus -> PC idea is going to severely limit your maximum sampling rate. The resolution of the built-in ADC of the microcontroller will probably also be less than or equal to 12 bits. I guess it depends on what you're measuring, but even a cheap USB scope would probably serve you better.

    An inverter is a DC-to-AC converter. You're talking about a DC-to-DC converter or a transformer, but those are typically used in power conversion. You'll need something different for instrumentation. (Edit: Just to clarify, it seems like you're talking about power converter topologies instead of measurement instrumentation. There exists, for instance, transformers for use in instrumentation, but they're built differently from their power converter counterparts).

    Those voltages are very high. Do you have experience in designing systems for voltages in that range?
    Last edited: Aug 30, 2014
  4. Aug 30, 2014 #3


    User Avatar

    Staff: Mentor

    You should stay below SELV = 60V to be safe for now. You do know what SELV is, right?
  5. Aug 30, 2014 #4
    sorry yes i meant converter. the voltage ranges i mentioned for example's sake, at the moment ive restricted myself to less than or equal to 24 VAC. I am basically in the process of designing a central hub which can change the I/O state of the subject circuit i want to analyze remotely, ( no geographically i mean i can toggle the state remotely from interface software i write on the pc.
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