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Anyone ever used Prop inputs to sense water ? — Parallax Forums

Anyone ever used Prop inputs to sense water ?

Don MDon M Posts: 1,647
in Propeller 1
I am building a device to sense water. I'll have a common probe (ground) in the water then 2 different probes at 2 different heights above the water. Want to sense when the water is rising to the different levels. I was thinking maybe tieing the inputs high with a very large resistance to prevent them from floating either way then when the water rises to the probe it makes a circuit to ground.

Comments

  • jmgjmg Posts: 15,145
    Don M wrote: »
    I am building a device to sense water. I'll have a common probe (ground) in the water then 2 different probes at 2 different heights above the water. Want to sense when the water is rising to the different levels. I was thinking maybe tieing the inputs high with a very large resistance to prevent them from floating either way then when the water rises to the probe it makes a circuit to ground.

    How long do you need this to last, how often will you clean this, and how clean is the water ?

    Simple passive probes need water less than 100% pure, but not too impure or the rise/lower of level leaves a conducting residue behind.


  • Don MDon M Posts: 1,647
    jmg wrote: »
    How long do you need this to last
    Forever ?
    jmg wrote: »
    how often will you clean this

    As little as possible to never.
    jmg wrote: »
    and how clean is the water ?

    It's wastewater. Think of floor drain or sewer backup.
    jmg wrote: »
    Simple passive probes need water less than 100% pure, but not too impure or the rise/lower of level leaves a conducting residue behind.

    Right now I'm using bared copper wire and yes I've noticed that it gets corroded and non conductive after a period of time (year?). Maybe stainless steel would be better? But my main question is whether the Prop inputs would sense the resistance of the water. I'll have to set up a prototype and see.

    My present circuit uses CMOS logic and works OK. I want to add some additional "smarts" to my device is all.


  • Peter JakackiPeter Jakacki Posts: 10,193
    You need to reverse the polarity of the pulse for the same duration that it conducts for to minimize the corrosion effect but high grade stainless is what you probably need to work with. This is easily handled by using 2 I/O and 2 probes to form the circuit. However you could easily use a non-conductive method such as RF absorption which could be implemented simply as an RC delay where you send out a pulse and measure its rise time with another input.
  • localrogerlocalroger Posts: 3,451
    Use floats and real switches above the high water line. Trust me you will regret doing anything else.
  • Don MDon M Posts: 1,647
    localroger wrote: »
    Use floats and real switches above the high water line. Trust me you will regret doing anything else.

    I may just do that. Thanks.

  • Beau SchwabeBeau Schwabe Posts: 6,547
    Use a capacitive approach and use sealed electrodes rather than direct contact
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