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PH Level meter.

Discussion in 'General Electronics Discussion' started by dchurch, May 17, 2013.

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  1. dchurch

    dchurch

    5
    0
    May 17, 2013
    Hi all,

    I'm a bit of a beginner at electronics, but have taught myself quite a lot over the last year or so.
    I recently bought a PH meter on ebay, and have soldered the wires out of it and into a breadboard. I have put my multimeter across the two points in the breadboard and I get the reading on the meter.
    I also have a usb Velleman card with two analog inputs.
    I'd like to be able to read the input into the card so I can report the PH level of soil to my PC. The PC part and the card reading I can do, it's getting the signal to the card I am stuck with.
    Can anyone point me in the right direction?
     
  2. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    Did your PH meter come with a probe, or did you just get the meter itself.
    Most probes I've dealt with are for testing PH in liquids.
    You might want to Google the model number of your meter, and get the facts about
    it's required probe, and capabilities.
     
  3. dchurch

    dchurch

    5
    0
    May 17, 2013
    Hi, thanks for the reply.

    It's one of these:

    http://www.ebay.co.uk/itm/320845653364?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

    It is a meter attached to a probe. Inside, it has three wires. One from a light sensor, one from the PH and one from the moisture. These are controlled by a switch on the front. I have taken the wire from the PH lead to a screw terminal that I have mounted on the outside.
    There is another wire that leads all three (depending on which is switched) to the meter; I have also taken that to a screw terminal on the outside to make amendments easier.
     
  4. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    You've got what you need, the probe and the circuit within the meter to read the values
    from the probe. I regret I an unfamiliar with interfacing the the usb card with a PC in
    an application like this. Hopefully someone familiar with the usb card will come on
    to help you.
    My experience with PH meters, is that the probe is designed to be read by the meter
    designed for it. Off-hand, I would believe that you can't just take the wires from the
    probe itself, and expect to read a value through the usb card to your PC. You're going to have to allow the probe to send a signal to the circuit in the PH meter, and
    read the value of the signal that is transmitted through the wires to the METER on the
    face of the PH Meter. That is the value you want to be sending to your usb card.
    Good luck with the project. It seems to me to be an interesting adaptation of a device
    into a computer.
     
  5. dchurch

    dchurch

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    May 17, 2013
    Hi, thanks for the reply. I shall continue to experiment.

    The one thing that I don't understand is that the device has no power - no batter and no solar.
     
  6. davenn

    davenn Moderator

    13,657
    1,888
    Sep 5, 2009
    its got a solar cell on the front of it :)
    it doubles as a light meter and it probably charges a button battery
    if no small internal battery then it will only run when there is light

    Dave
     
  7. glewis721

    glewis721

    49
    1
    Apr 30, 2013
    what kind of output does the PH meyer give?
    if its a analog one, them you could use a voltage divider, arduino, and the sketch attached to the end of this post to print the level directly to the serial monitor and skip the card.
    if its a digital one, then i got nothing
     

    Attached Files:

  8. glewis721

    glewis721

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    1
    Apr 30, 2013
    i fail to find said solar cell.
     
  9. dchurch

    dchurch

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    May 17, 2013
    If I cover the 'solar' cell on the front with my finger, the device still works...and there's very little inside it...no button battery.

    I'll take a photo when I get home later (then you'll likely see my dodgy soldering!).
     
  10. davenn

    davenn Moderator

    13,657
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    Sep 5, 2009
    if you didnt recognise the solar cell its possible you dont recognise what it may be charging ;)

    Dave
     
  11. dchurch

    dchurch

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    May 17, 2013
    I'm fairly certain that the 'solar' cell on the front is the light sensor (there's a three way switch on the front of the device | moisture | light | PH |.

    I swear there's no battery inside.
     
  12. glewis721

    glewis721

    49
    1
    Apr 30, 2013
    i still cant find the solar cell--
    can you please describe where it is davenn?
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    I'd be 99% sure this uses dissimilar metals in the probes to do all the magic
     
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