RS232 voltmeter

Discussion in 'The Projects Forum' started by siqu, Feb 28, 2013.

  1. siqu

    Thread Starter New Member

    Feb 28, 2013
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    Hi out there.

    Im thinking to build a voltmeter , and the values should be red on the pc trugh a rs232 connector.

    I was thinking to use a shunt then some analog then a uC and rs232.

    Any ideas or do you know any projects similar that i could use as help.

    Thank you ..:)
     
  2. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    If its a voltmeter only, as you stated, then why not just read the voltage with the ADC in a micro and send it to the PC over RS-232. You don't need a shunt.

    Maybe some protection circuitry and an op-amp buffer to protect the micro. Maybe a range selection switch for different votlages.
     
    siqu likes this.
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,654
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    If I may, below are URLs to some of my projects as examples of what's been done along those lines with AVR controllers. The last link, for AttoBasic is to a series of chips with flash-resident basic interpreters which make very compact data collecting computers. The examples are 8 and 10 bits.

    http://cappels.org/dproj/VR/AVR_Data_Logger_and_Voltage_Recorder.html

    http://cappels.org/dproj/morbcn/morbcn.html

    http://cappels.org/dproj/minmassrfM8/minmassrf8.html

    http://cappels.org/dproj/AttoBasic_Home/AttoBasic_Home.html
     
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  4. siqu

    Thread Starter New Member

    Feb 28, 2013
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    Thank you for your reply.

    Im found out so far that i gonna use a MCP6001 opamp to amplify the incomoning signal from my shunt resistor.

    I also deside that i want to use a adc to convert the analog signal to digital , and send it to a micro , exacly as you say.

    But my next problem is now , that i dont know wich ADC i schould use ?
    My opamp is MCP6001 and what keind of resolution do you think that i need to use ? I want this projekt to be stabile but "easy" . Im new in this world.

    Sorry if my spelling isnt good, im from Danmark
     
  5. siqu

    Thread Starter New Member

    Feb 28, 2013
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    Thanks for the URL´s. I will read them and se if i understand anything.
     
  6. siqu

    Thread Starter New Member

    Feb 28, 2013
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    I have a mcp3008 ADC, can i use this one for my projekt ? And why ?
     
  7. DickCappels

    Moderator

    Aug 21, 2008
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    Yes, you can use it because it is an A/D converter.

    You would still need something to sit between the RS-232 line and the MCP3008. The thing in-between would send control signals to the MCP3008 and take the readings from the MCP3008 and format them as decimal numbers and convert them to a serial data stream for translation to RS-232 voltage levels. It would be a very complex random logic design exercise, though it might be possible with great perseverance. Or you could connect an microcontroller to the MCP3008 and the RS-232 driver (such as the old standby, MAX232) and do it with firmware.

    Many microcontrollers have 10 A/D converters, thus saving a chip.
     
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  8. siqu

    Thread Starter New Member

    Feb 28, 2013
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    Thank you so moutch for reply, cuz im running out of time for this projekt.

    But i need to document why i choose the mcp3008 AD-converter. Can you help me with that ? I mean, why is MCP3008 god for this my projekt.

    I was thinking about to use a raspbarry pi between the AD and RS-232.. I have these things at home that's why.
     
  9. siqu

    Thread Starter New Member

    Feb 28, 2013
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    0
    And why 10bit for this projekt ?
     
  10. DickCappels

    Moderator

    Aug 21, 2008
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    You could probably use the MCP3008 with a Raspberry Pi. I know very little about Raspberry Pi.

    Why is the MCP3008 a good choice for the project? I leave that to you because you are making the selection. Availability is a valid criterion; you should only use parts that are available.

    Why 10 bit? You have not mentioned the resolution you want to have. For some applications, 10 bits is enough. For other, higher resolution measurements are needed. In other words, if 1 count in 1023 is adequate for your use of the voltmeter, then 10 bits is enough.
     
  11. panic mode

    Senior Member

    Oct 10, 2011
    1,320
    304
    we know nothing about your project and we can't tell why you chose this chip when there are so many alternatives. reasonable guess is that your project:
    a) only needed 10bit resolution (you could also use 24bit if you like)
    b) only needed single sided analogs (instead of differential)
    c) needed multiple channels which was not available on controller you had chosen and you could not pick bigger chip (controller with more resources)
    d) would be fine with ADCs that are already in the controller but you didn't bother to check the datasheet so being ignorant and planet hating guy you are, you just picked external ADC to offend those who create efficient and make elegant designs
    e) ADCs on your controller ware lower resolution (such as 8-bit and for you this was not enough - so you picked 10-bit as better option)
    f) perhaps your you were running out of pins on your controller, hence you opted to use external chip such as MCP3008 and serial interface which gave you 8 inputs by using only 3 pins on controller
    g) you simply had no idea that there are ADCs in your controller (lame)
    etc.
     
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