Water Sensor and Pump Relay

Discussion in 'The Projects Forum' started by vtschu, Nov 6, 2012.

  1. vtschu

    Thread Starter New Member

    Nov 6, 2012
    4
    0
    Hi all,

    Recently, I bought a Netduino MC and started to program it (I am a software programmer) to do stuff. I quickly realized that I needed to understand electronics if I was going to do cool stuff (other than blinking a LED) with my new toy.

    I started reading and doing tutorials like a madman, but started to burn out with no practical applications. Until...

    I have a situation where the overflow for my water filter brine tank has nowhere to drain. It has been fine for 11 years, and the other day the valve stuck and filled my living space with 1" of water while we were at work.

    I purchased a 12v/2A marine water pump which I rigged into a sump tank with a 12 volt car battery. This pump cycles every 2.5 min to see if any water is present then shuts off (if water is present it pumps until dry). I don't really like this solution.

    I designed a water sensor/pump relay that works great on the breadboard. I want to solder it to a PCB and put it to work, but I want someone to critique it first. Hopefully I have attached the photo successfully.

    The sensors are simply wires connected at intervals on a plastic tube. I have tested it on our tap water, it works fine. My guess it will work even better in water filter brine.

    Too many diodes? Have I created something that could be more simply with a chip?

    Thanks for any feedback.

    -N00b electronics guy
     
  2. williamj

    Active Member

    Sep 3, 2009
    180
    32
    vtschu,

    I've looked over your design for the pump control and it all looks pretty good. But I'm no expert in solid state circuitry, so if there's anything amiss in that respect someone else is bound to speak up. However something else did occur to me as I was looking it over.

    How do you know when your battery is running low or all together dead? One solution is to just purchase a battery management system sized for you battery. But then again there's another thing that pops up. Would running the pump motor interfere or damage the battery management system while it's still connected?

    One possibility is to connect an additional relay to the pump control circuit that would switch from the battery management system over to the battery while the pimp motor is running and then back to the battery management system after the pump motor has shut off.

    Just something I noticed.

    Good Luck
    williamj
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    Using DC excitation on the continuously submerged "Low Sensor" electrode will eventually cause it and the ground electrode to corrode due to electrolysis.

    Ken
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
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    kmoffett is absolutely correct..

    Use proper reed float switches/or optical switches.
     
  5. vtschu

    Thread Starter New Member

    Nov 6, 2012
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    0
    Thanks William and Ken, that is the kind of feedback I am looking for.

    William, I have purchased a 12 V power supply that is rated for 2A that I intend to use to replace the battery (don't really like having lead acid battery in the house).

    Ken, I looked online for water sensors but I really didn't find anything for a reasonable price. There is this, but I think the device is not designed for full immersion either. I also know that having voltage across electrodes will cause them to corrode over time. Any suggestions for a more robust electrode would be most welcome.

    The diodes I put after each transistor were done more on instinct than with any real guidance. I was paranoid that somehow closing those circuits and having a motor running on the same power leg might cause the current to reverse. Silly, I know, but I like the idea of a one-way valve that has minimum effect on current.

    But, also, keep in mind that this whole thing will be dry almost all of the time. It will act as backup should my brine tank valve stick again. If it happens with any frequency, I will be calling the company that services the system.

    Mostly, this was a chance for me to try to apply some of the things I was learning from books/online to a real world solution.

    My next foray will be into the 555 timer and its uses... haven't thought of an application yet.

    Thanks for your help.
     
  6. vtschu

    Thread Starter New Member

    Nov 6, 2012
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    Thanks, mcgyver.

    I found some polypropylene reed float switches at Mcmaster-Carr for about $10.00 each. I certainly could use them instead of electrodes.

    Optical switches look like the way to go, but are outside of my hobbyist budget. :)
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
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    Mcmaster has good quality products.. You can find cheap float switches on ebay for like $1 but the quality leaves a lot to be desired. Something like a float switch is not something you want to fail.
     
  8. williamj

    Active Member

    Sep 3, 2009
    180
    32
    vtschu,

    A 12V power supply will work for day to day operation but what of a power failure and a leak at the same time? A belt and suspenders isn't always a bad idea.

    just a thought,
    williamj
     
  9. vtschu

    Thread Starter New Member

    Nov 6, 2012
    4
    0
    Thanks williamj, battery backup is a good idea, especially up here in the puckerbrush. I will incorporate it into my circuit with a relay to switch to battery when power fails.

    I found an error in my circuit as I was moving the components off the breadboard and onto the circuit board. The "Low Water" LED is tied to the collector side of the transistor. That can't be right, so I think it needs to be tied to the "A" contact of the SPST relay so that the LED will light when the low water switch is closed.

    It is kind of interesting that I drew it wrong, but when I went to the breadboard I put the tie-in for the LED in the right place. Gotta stop doing this stuff at midnight.
     
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