Turbidity Meter

For the subject of measuring water, we had to make our own sensor. We were allowed to choose which phenomena to measure. We chose to make a turbidity sensor. By following this instructable you will be able to make this sensor yourself!

Materials

• Arduino Uno
• Breadboard
• Cables
• Light sensor
• Resistor ( 5k ohm)
• LCD
• Item profile (+/- 45 cm)
• Laser
• Straws
• Sensor holder (laser printed)
• Laser holder (laser printed)
• Sample holder (laser printed)
• Jar (see-trough)

• Connect the laser to 3V and GND
• Connect the sensor as in the picture
• The LCD screen can be connected as follows:
• GND to GND, VCC to 5V, SDA to A4 and SCL to A5
• Use a 5K-ohm resistor (You can measure the variable resistor using a Volt meter)

Use a volt meter to measure the resistants through the variable resistor.

Laser print the holders for the laser, sample, and LDR sensor. Use the template below, print on wood preferably on 6 mm plywood.

Place the holders in the ibrium profile so the setup looks like the image above.

Place the LDR in the straw and place the straw in the holder. The black straw prevents background light. If the light shines through the straw, make it dark by adding thick black paper around it.

You can turn the laser so the light falls directly on the LDR.

Use our code to read off the Volt and NTU values at the display.

We put the display in a box, which is not necessary but it makes the display easier to read.

Use paper to make sure the laser points directly at the LDR. You can check the intensity with the Volt output (5 V is 100%).

Put your sample in a see-through jar, and read the NTU and Volt values of the display. Write the values down for the calibration. We found the following values:

Water = 0.8 NTU (4.64 volt)

Coca Cola = 2.2 NTU (2.74 volt)

Coca Cola zero = 10.5 NTU. (1.8 volt)

Use the following Python code to calibrate the sensor and display:

import numpy as np

from scipy.stats import linregress

def poly(fitted, obser):

  err = obser - fitted

  S = np.sum(err**2)

  E = np.sqrt(1 / (len(obser)) * S)

  return E  

y = np.array([0.8, 2.2, 10.5]) #NTU

x = np.array([4.64,2.74,1.75]) #volt

pol2 = np.polyfit(x, y, deg=2)

c = pol2[0]

d = pol2[1]

e = pol2[2]

g = c * x**2 + d * x + e

print(f'c = {c:.2f},d = {d:.2f},e = {e:.2f}'

This step is optional. But it makes the device more presentable and easier to carry around.