Water Velocity Meter

This measuring device can measure the velocity of free-flowing water.

Materials:

1. 1m long Tube (PVC) with a 30mm diameter, 3mm thickness and a bend as can be seen in the photo
2. Metal wire with a 1mm diameter
3. Standard PLA
4. 6 small neodymium magnets with 8mm diameter and 2mm thickness
5. 1 roll of duct tape
6. 15cm long tube (PVC) with 70mm diameter and close on one end
7. A box 170x120mm or approximate dimensions made of PVC with a see-through lid which can be screwed on
8. An Arduino Uno
9. A breadboard
10. Approximately 30 wires
11. A battery pack to connect to the Arduino Uno
12. Batteries
13. Display screen 1602A
14. A Hall sensor
15. Hot glue gun with glue sticks
16. A drill
17. 10mm drill bit
18. 3mm drill bit
19. Screwdriver

Facilities:

1. 3D printer with a minimum bed size of 20x20mm
2. 3D printing software (Creality print was used to build this device): https://www.creality.com/pages/download-software
3. Arduino software: https://www.arduino.cc/en/software

First, the wheel needs to be 3D-printed. Use the attached stl-file. Using standard PLA, you can start printing while keeping the following settings:

1. 20% infill
2. 0.2mm layer thickness
3. No supports

This print should take about 3 hours so you can continue with step 3 until this is done. After it is done, remove the extra bits on the edges of the part.

Using duct tape, stick the magnets onto the wheel. This should be done on the outside edge of each spoke of the wheel as is made clear in the photo.

An important note is that the magnets should face the same way with the negative side pointed towards the outside as illustrated in the photo. To know which side is which, use the hall sensor to determine the side. Moving the magnet toward and away from the hall sensor allows you to check whether the graph moves down when the magnet gets closer. Use the attached code and Arduino setup to check this. Open the serial plotter to see the graph.

Attached is a setup layout. Apart from connecting the hall sensor, you can use singular wires to connect everything. The hall sensor will be mounted at a later stage. It will be close to the wheel and away from the Arduino board so we need to make a longer wire to accommodate this. Attach 5 wires to get enough length. Use duct tape in the connecting sections to ensure they don't come loose.

Take the long PVC tube and get your drill with the 10mm drill bit. Drill a hole in the middle of the tube and make sure it only goes through one side. Drill another hole on the bend, again making sure it goes through one side.

Then put the long wires that you made to connect the hall sensor through both holes. So it should go through one and come out the other. After that, you can connect your hall sensor.

Now that the hall sensor is connected to your Arduino with the wires going through the long tube, you can attach the hall sensor to the wheel attachment. This is the smaller tube with one of the ends closed. Stick the hall sensor onto the outside of the tube on the closed end using duct tape. Make sure it is centred.

Now we attach the wheel to the small tube with the closed end pointed towards the wheel.

First, grab the metal wire and put it through the hole in the wheel. Make sure you have an even amount of wire sticking out on both ends and proceed to bend the wire 90 degrees. Both wires should be pointing in the same direction.

Then stick the two ends of the wire to the sides of the small tube using duct tape. There are two important things you need to keep in mind when doing this:

1. Centre the magnet on the edges of the wheel to the hall sensor which is stuck on the bottom of the small tube.
2. Mount the wheel as close as possible to the tube to make sure the magnets on the edges of the wheel can get as close as possible to the hall sensor for better reading.
3. The wheel should still be able to spin freely without hitting anything

The wheel assembly can now be attached to the support structure. You should still have some metal wire sticking out above the small tube. Use this part of the wire to attach the wheel assembly to the support structure using duct tape. Use enough duct tape as there should be minimal play as this affects measurements.

Grab your PVC box and drill three 3mm holes in the bottom. Place it on the bent part of the tube as can be seen in the photo. Pull the wires you used to connect the hall sensor through these holes so you can connect them later to your Arduino which will sit in the box.

Hot glue the box to the tube to secure it, then migrate your Arduino setup to the box. The display screen should be visible as seen in the pictures. The lid should be able to close to place your electronics in the box appropriately. Be careful when doing to not disconnect one of the wires by accident.

Now that the setup is done, you can upload the code that converts the sensor readings to water velocity. First, you need to check the rest value of the hall sensor. Do this by manoeuvring the wheel so the hall sensor is between two spokes. Then use the Magnet_checker.ino file from step 2 to get the graph for the hall sensor's values. Fill in the rest value of the sensor in lines 34 and 66, replacing the number 480.

Then connect the Arduino to your laptop. Now upload the code to your Arduino using Arduino software. You can find the code attached. After that, you can disconnect your laptop and proceed to connect the Arduino to the batteries.

Congratulations, you have now completed the build of the water velocity meter! You can now use it in the field.