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choosing a resistor value

Discussion in 'General Electronics Discussion' started by mikgol, Apr 13, 2016.

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  1. mikgol

    mikgol

    87
    1
    Jul 6, 2013
    Hey electronics guru's,

    I want to detect water level with an arduino by feeding 5v through the water and reading the voltage through an analog pin.

    I want to avoid electrolysis as much as possible - how can I find the max resistor value I can use which will allow me to detect water but not pass too much current through the water?

    I've been looking through tutorials and sometimes a 10k resistor is used, sometimes no resistor, so I'm not sure what to do.

    The electrodes are stainless steel and it's in drinking water - electrolysis corrodes stainless steel to make a toxic chemical, so I want to avoid poisoning my animals :)
     
  2. Kiwi

    Kiwi

    330
    78
    Jan 28, 2013
    What about a plastic float switch?
    Ebay has heaps of different types.
    Depending on what you want the switch to do, you could possibly not need the Arduino.
     
    duke37 likes this.
  3. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    What about an ultrasonic distance module?
    What about a capacitive probe?
    What about a platinum electrode?:)
     
  4. Herschel Peeler

    Herschel Peeler

    401
    65
    Feb 21, 2016
    Why do you need an Arduino? Are you going to monitor this level over time? If you just want to know there is water no smarts are necessary.
     
  5. Anon_LG

    Anon_LG

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    117
    Jun 24, 2014
    Or a graphite electrodes, if platinum is a little outside of your budget.
     
  6. mikgol

    mikgol

    87
    1
    Jul 6, 2013
    Cheers for the replies guys. I started out making a float solution, but decided on a non-moving solution because the float would sometimes get jammed, and was taking up too much space in the dog bowl.

    As it's for a dog I want to use "food grade" materials (not sure what kind of chemicals a float would slowly release into the water) so I decided on food grade stainless steel.

    I also want 2 probes - one to detect "full" and one to detect "empty" (i.e. if water level goes lower than the bottom probe) - so I can't accomplish this with an ultrasound sensor (which is a shame, as I'm sure sound waves are "food grade").

    So, I guess I'll have to figure out what resistor to use with trial and error. I appreciate all the ideas and input, thanks guys
     
  7. flippineck

    flippineck

    269
    9
    Sep 8, 2013
    Could you place the dog bowl on some kind of plinth containing the sensor out of a set of kitchen scales, and use the arduino to look at the weight in grammes?
     
  8. mikgol

    mikgol

    87
    1
    Jul 6, 2013
    Yep I guess that would work too, a good idea but I want to eventually make a product so I think that solution would be too expensive compared to electrodes
     
  9. flippineck

    flippineck

    269
    9
    Sep 8, 2013
    Another possible sensor arrangement based on refraction

    http://sciencelearn.org.nz/Contexts/Light-and-Sight/Sci-Media/Images/Refraction-of-light-in-water

    Fit some sort of light beam at an appropriate height just above the 'full' mark, with the beam angled down slightly. The beam should then strike different parts of the opposite wall of the bowl depending upon the height of the water. Possibly even the floor of the bowl.

    You'd have to do some (easy if you are ok with relatively basic maths) geometry and calculations involving Snell's law and trigonometry to work out exactly where the light beam will strike the wall of your bowl (or you could just use trial and error)

    Off the top of my head I can guess there might be problems with reflections, ambient light or insufficient light ray deflection, then again there might not be. I've no idea of the cost of suitable light source and detector components, you might be able to pick them up for pennies or you might not.

    Just wondering why you need 2 probes / sensors.. my understanding is that if you only had one, you'd still have a two-state signal, either it sees water or it doesn't. For Instance if you were using a solenoid valve to turn the water supply on and off, it just needs to be turned 'on' when the sensor fails to detect water. When the sensor sees water again, turn off the valve.. adapting that to the light idea, could you use a phototransistor to act as a switch?

    If the beam is hitting the transistor, that means 'not enough water', current flows through transistor and solenoid valve, water supplied. When water interrupts beam, beam is deflected away from transistor, valve shuts.

    You have some specific need for a discrete, independant 'empty' sensor?

    BTW, if you develop one of these bowls and bring it to market, can I be your first customer? My cat is currently drinking out of the toilet cistern (it's missing it's lid :-( ) but seriously - she does this because the constant topping up makes the water extra cold so she prefers it to all other sources of water.
     
  10. duke37

    duke37

    5,364
    769
    Jan 9, 2011
    You can get drinking bowls for pigs, they turn on the water as they need it. Can you train your dog to be as intelligent as a pig?
     
  11. ChosunOne

    ChosunOne

    368
    90
    Jun 20, 2010
    Lavaguava's graphite electrodes actually sound like what you're looking for. Graphite is chemically inert at temperatures below its combustion point: It won't react with the water (or anything dissolved in it) through electrolysis. You can get ready-made graphite electrodes for your prototype by disassembling cheap carbon-zinc cells, or even any spent alkaline cells you have lying around the house--but the cheap carbon-zinc ones are easier to take apart.

    The last time I extracted these graphite rods for electrolysis, the rods were embedded in a metal cap on one end. You may need to dip that cap in wax or something to seal it off from the water.
     
  12. mikgol

    mikgol

    87
    1
    Jul 6, 2013
    There's some great ideas here! So many creative different ways to solve a problem, things I hadn't even thought of.
    For simplicity, reliability, and low cost I'm still leaning towards the electrodes method.
    Thanks so much ChosunOne for pointing me to Lavaguava graphite electrodes - I'll research more into those but that sounds like exactly what me and the dog needs :) Failing that I can train my dog, but I'm not sure she's smarter than a pig :)
     
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