Open Flow Meter

An Arduino powered flow-meter for use in geography river studies and environmental monitoring projects

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Build a flow meter to measure water speed in rivers.The current build shows water speed in Km/h and costs about 60USD for all the parts (a typical off the shelf unit will cost about USD1000).

Flow meters are great tools for river surveys but are often prohibitively expensive, especially for secondary schools and field studies centres. LabQuest has somewhat of a monopoly on these sensors for use in schools and we think its high time there is an easy to make, low cost and hackable solution for these tools. Here I'm using an Auduino, plus touch screen shield and a 'flow volume sensor' designed for measuring flow volume in plumbing.

Field Test:
They are multiplying:

The build 20th of January 2021:

Improvements since the DN50 build: Internal battery housing, on/off switch, aviation connector, DN80 sensor, detachable sensor pole.

Here is one of the earlier designs using an DN50 sensor.

I have switched to using a DN80 sensor, I have created a new Arduino housing that now has an on/off switch, an aviation connector for the main cable and internal battery housing. I'm working to change the firmware to read MPS instead of Km/H.
After that I will do some tweaking comparing the readings with a purpose build flow meter to increase the accuracy. If all of these steps go as planned then I will complete the build instructions and finish this project.

Arduino hosing n battery 2.FCStd

FreeCAD Auduino Housing

fcstd - 6.96 MB - 12/17/2020 at 05:57


DN80 mount.FCStd

FreeCAD Sensor links

fcstd - 4.40 MB - 12/17/2020 at 05:56


  • 1 × DN80 water sensor 3"
  • 1 × Arduino Uno R3 (clones also work)
  • 1 × HiLetgo 2.4 Inch TFT LCD Display Shield Touch Panel ILI9341 240X320 for Arduino UNO MEGA
  • 1 × length of 3 strand wire (we used silicon copper wire as its really soft and flexible)
  • 1 × set of 3D printed parts From:

View all 10 components

  • Added meters per second readout

    Eben03/29/2021 at 11:27 0 comments

    The new calibrated version of the skit file is ready for download under V5 from our Gitlab.
    We added meters per second to the display readout so now you can see both Kph and M/S.

  • Calibration

    Eben03/27/2021 at 15:32 0 comments

    Calibration with a commercially made flow meter:

    In the image above we have the commercial flow meter on the left, a m/s to km/h conversion in the centre and the open flow meter on the right.

    At first the open flow meter was providing a reading 4 times faster than the reading from the commercial unit, but after adjusting some settings both units give quite similar readings. Additional work needs to be done, however so far this will be more than good enough for GCSE, A Level and IB students usage.

  • Battery Lid

    Eben12/29/2020 at 08:31 0 comments

    The battery lid now fits better and the new version has been uploaded to: Make sure to print the new version as the old version did not fit!

  • 24 hour submersion test

    Eben12/25/2020 at 04:53 0 comments

    Here I leave the sensor in water for 24 hours to see if the silicon waterproofing of the electronics works.

    When I switched on the control box and turned the prop, it still worked as before, so I'm happy enough with this waterproofing technique for now.

  • First complete unit

    Eben12/24/2020 at 15:03 0 comments

    Here is the first fully assembled unit:

    It features an: on/off switch, aviation connector, rechargeable battery, configurable intervals for taking speed tests and has a quick detach system from the ranging poll (this means we can carry less on field trips by using the range poll to hold the flow meter).

  • Sensor testing

    Eben12/19/2020 at 03:50 0 comments

    I tested a range of different pipe sensors at the start of this project back in April 2019:

    I wanted to use the small clear sensor shown on the far right, however it could not measure slow moving water. The first sensor I built that was used for field work in a test was using the DN50 (the large black sensor, centre left of the image). But it still did not perform well in slow moving water.
    The current build is now using the DN80, the one on the far left of the above image.

View all 6 project logs

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Dan Maloney wrote 12/18/2020 at 22:16 point

Yes, my sensor is a smaller version made for 3/4" pipe, and I calibrated it while it was plumbed up to such pipe. In my case, the exact volume needs to be known, but it seems like the number needs to be more relative in your application.

  Are you sure? yes | no

Dan Maloney wrote 12/17/2020 at 17:55 point

I'm curious how you calibrated the flow sensor. I'm working on a similar project ( and managed to get my sensor calibrated gravimetrically. Wondering what method you used.

  Are you sure? yes | no

Eben wrote 12/18/2020 at 13:03 point

Thanks for sharing. Am I right that your system is to measure flow volume (litres of water pumped per unit of time)?

I'm working on a sensor that can be put on a poll to measure flow speed in a river. In your case it should be easier as the pipe sensor you have is designed for measuring volume. I brought quite a few different pipe sensors to test out but settled on the largest one I could find as that was able to give better readings in slow moving water.
I'm not aware of anything to calibrate on the sensor. It just pulses once for every rotation of the prop and you can use that combined with knowing the width of the pipe to measure how much water passes through.
I will update my project here once I get the hardware sorted out a bit more about the accuracy of the unit. However for my use case it dose not need to be very accurate, it's just for teaching children how to do data collection in the field (the data they collect is not going to be used for anything).

  Are you sure? yes | no

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