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Sensor choice for pond water depth

Discussion in 'Sensors and Actuators' started by Ian, Sep 1, 2017.

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  1. Ian

    Ian Administrator

    Aug 23, 2006
    We've got a small pond in our garden, but with the warmer weather in summer I will often need to top it up manually with water when the level gets too low. I thought it might make for an interesting project to have a battery powered IoT device (likely ESP8266 based) track the water temperature and water level.

    I've found a waterproof temperature probe that should be fine for temperature measurements, but I'm looking for suggestions on measuring the water level (the pond is around 50cm deep). There are plenty of float sensors, but they only appear to give high or low sensing (which isn't ideal).

    What would your suggestions be for a low-power, low-cost water level sensor be? Would a submerged pressure sensor be the best way, waterproof ultrasonic sensor, or are there alternative float sensors that would enable me to take level readings?
  2. shrtrnd


    Jan 15, 2010
    How about a stick permanently located. If labeling with measurement increments isn't aesthetic enough, maybe a cleverly disguised (artificial) water plant with flowers marking depth increments.
  3. Ian

    Ian Administrator

    Aug 23, 2006
    Ah but where's the fun in having a non-electronic method ;). I'm more doing it for a bit of fun, with a practical purpose as a secondary consideration - I'd be interested to log the data too, so that I can see trends throughout the year (could be useful to predict when the goldfish will spawn).
  4. dorke


    Jun 20, 2015
    I think the simplest way to solve the original problem of avoiding the manual operation of the filling pump
    Is 2 wires submerged in the pool at the point(level) of the "full water" in the pool.
    Since the pool water is conductive once the water reach that level a low resistance will be present.
    that can be used to stop the pump.
    Another 2(1) wires at a lower water level could be used to activate the pump.

    The idea is very simple and you can play around with it.
    Hysteresis is needed to avoid the pump from switching on and of at the full level.
    It can be made to work with only 2 wires.

    If you do want to measure the water level continuously ,a float device may be useful.
    Like the one used in auto fill toilet to mechanically move the lever of a slide potentiometer etc.
  5. kellys_eye


    Jun 25, 2010
    Seconded - I use a similar system to keep my hens water supply topped up - might do this for the pond too (6000 litres) - but neither have a potentiometer fitted at the moment. Sounds like I should be doing this to supplement my proposed remote water supply monitoring project (we have a weir and collection tank for domestic water).

    Problem with the pond arrangement is that the water level migh only change by an inch before you consider topping it up and I'm dubious of the accuracy of a level/pot arrangement for such a small movement.

    I've seen the water level sensors in my F-in-laws boat (domestic water) that consists of a float that rides up/down a post. Float has a magnet and the post has reed switches but the depth change is considerable (half a meter and more). The fuel tank sensors are the float/lever type though.

    @Ian - if you get a system going then please post the result here so I can copy you!
  6. BobK


    Jan 5, 2010
    Yep, my pond has a mechanical float based auto-fill valve.
  7. Ian

    Ian Administrator

    Aug 23, 2006
    Thanks guys - I'll check out the float/potentiometer method and see how doable it would be. Our pond is only small (and is raised), so I can't easily get it to auto-fill without running pipes above ground (although if I was to build a pond from scratch, I'd definitely do this).

    Will do :)
  8. Alec_t


    Jul 7, 2015
    Capacitive sensor?
  9. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Consider an LVDT with a float attached to the core. The M-12 series, available from might do it for you. Several stroke lengths are available, but the M-12 100 (±100 mm stroke) seems appropriate for your task.

    If you want battery IoT operation, LVDT excitation will have to be intermittent, perhaps on command through a coded network link, since continuous excitation would soon deplete the battery. And even an inexpensive LVDT might be too much cost for this home project.

    An alternative sensor is the Texas Instruments inductive sensor LDC1000 which can be configured as a "poor man's" LVDT. This is available integrated with a TI microprocessor and a USB interface.

    Attached Files:

    Ian likes this.
  10. Ian

    Ian Administrator

    Aug 23, 2006
    Thank you all for the replies - some of the methods like the LVDT would be too expensive for this project unfortunately, as it's just for a bit of fun. I was hoping to do the build for under £20 or so - I've got most of the components already, so should be doable with a bit of planning.

    I think I'm going to go down the route of using an ultrasonic sensor to measure the pond level, as they're cheap and should give reasonably accurate measurements. The JSN-SR04T is only ~£7, but it has a minimum sensing distance of 200mm, which I may need to work around with placement.

    edit: I found this continuous liquid level sensor, but it's a bit expensive for a useless project: - it looks nice though, so I'll see if it's possible to create something similar.
    Last edited: Sep 2, 2017
  11. Irv


    Jun 7, 2017
    How about a series of hall sensors sealed in a plastic tube, with a ring magnet attached to a float sliding up and down the tube?
    Ian and davenn like this.
  12. Bluejets


    Oct 5, 2014
    The pot idea seemed simple enough. Could be further expanded to an lcd readout without too much trouble but unnecessary I think.
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    If using a method involving conduction, I'd AC couple the signal to the probe. This will reduce problems with electrolysis.

    If you have the signal probe deepest in the pool and a series of probes each shorter than the previous one, you should be able to get an indication of the level. With a little engineering, you should be able to do it all in a single long probe.
    Ian likes this.
  14. ritesht


    Jan 6, 2019
    Sorry for bumping up an old question but I’m in the same boat of requirement.

    And to my surprise there are quite a few new sensors in town:

    This one has 2 transducers instead of 1 therefore has less minimum detection distance as compared to JSN SR04T. It is also completely sealed and waterproof.

    Before finalizing on this I had bought another one which was a waterproof modified version of HC-SR04 from here

    The 1st one is much more rugged and waterproof as compared to the latter one.
  15. Bluejets


    Oct 5, 2014
    Ultrasonics units like this always have 2 elements.
    One is the transmitter and the other is the receiver.
  16. Ian

    Ian Administrator

    Aug 23, 2006
    Many thanks, I hadn't seen some of these models before. I ended up putting the project on hold, but I'll check out the specs of these sensors as I'm still keen on building it.
    ritesht likes this.
  17. ritesht


    Jan 6, 2019
    Yes. Some have only 1 transducer and that same transducer is used as both transmitter and receiver, as is the case with JSN-SR04T. Because of this the minimum distances are high because the same transducer needs time to switch from transmitting mode to receiving mode. Having 2 transducers nullifies this problem and therefore gives lesser minimum distances.
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