Water Turbidity

1. What is Water Turbidity?

Turbidity is the measure of relative clarity within water, and it is a crucial factor in determining the water quality of a sample. In this unit, we tested a grove turbidity sensor with a seeed xiao RP2040 chip, assessing samples' conductivity with differences in 1) opacity/transparency, and 2) the presence of sediments or suspended particles. This sensor measured the turbidity of water using the "refraction of wavelength" between the photo transistor (which detects different light levels + converts light levels to electric current) and the diode. Converting the values to a voltage output, it relayed the conductivity of the different samples. For this lab, we utilized four different samples: clear tap water, cleaner Lake Latin water, dirtier Lake Latin water, and muddy water.

2. Programming the Grove Turbidity Sensor

Provided Arduino code

For our different samples, we utilized an Arduino code that was provided to us. Under the void setup(), which only runs once, it initializes the serial monitor and sets the data rate of 9600 bits per. sec between the Arduino board and the monitor. Then under the void loop(), it takes the rate of the sensor at analog pin A0, converts the binary value to voltage, and prints it out on the serial monitor. For this code, the max voltage was 3.3 volts, so all values would be less than that. Finally, the delay(1000) line spaces out each voltage output by 1000 milliseconds, or 1 second. For dirtier/murkier water, the turbidity voltage output would be lower, whereas for cleaner/more transparent water, the output would be higher.

3. Comparing Different Samples

All four samples

Expansion board with RP2040

RP2040 connected to the turbidity sensor

Full set-up: turbidity sensor and RP2040 fully connected to the computer

Materials:

1 Grove turbidity sensor
1 RP2040 chip
1 breakout board
1 USB-C wire
Four water samples

Applications

Arduino IDE

Procedure

Collect four water samples, preferably two as the baseline measurement and two as
Connect the grove turbidity sensor to the RP2040
Plug the sensor into the computer with the USB-C wire
Import the provided Arduino code into the Arduino IDE application
Upload the code and open the serial monitor
Insert the sensor slot into the first water sample, noting how the voltage output on the serial monitor changed
1. The lower the voltage readings are, the higher the turbidity is (for murkier samples)
2. Likewise, the higher the voltage readings are, the lower the turbidity is (for clearer samples) :p
Repeat step 6 with the other three water samples

Links

For the first test, we used the clear water sample, collected from the water fountain. After uploading the code and inserting the grove turbidity sensor into the sample, we found that the voltage output averaged 1.07-1.09 volts. Because this was the first sample, we used this as one of the baseline measurements.

Set-up of first sample with the turbidity sensor

IMG_6948.MOV

Testing the first sample

Sensor output (V) on the serial monitor in Arduino IDE, averaging 1.08 V

For the second sample, we collected mud from a nearby field and mixed it with water from the water fountain. When we inserted the sensor, we found that the readings were significantly lower than that of the clean water, averaging around 0.22-0.24 volts. This was the second baseline measurement, as it showed how the sensor reacted with the opposite type of water.

Set-up of the second sample with the turbidity sensor

IMG_6947.MOV

Testing the second sample

Sensor output (V) on the serial monitor in Arduino IDE, averaging 0.23 V

For the third, test we used the relatively clean water sample taken from Lake Latin. Before testing it, we gave it a stir to ensure that all the sediments were relatively distributed. For this sample, we found that the voltage output was slightly lower than that of the clean water, indicating that it was less clear (higher turbidity). It averaged 1.05 volts.

Set-up of the third sample with the turbidity sensor

IMG_6945.MOV

Testing the third sample

Sensor output (V) on the serial monitor in Arduino IDE, averaging 1.05 V

Next, we tested our fourth sample, the dirtier water from Lake Latin, which was slightly more yellow in color. Similar to sample two, we gave this sample a stir and inserted the turbidity sensor. The results followed our predictions, averaging an output of 0.99 volts.

Set-up of the fourth sample with the turbidity sensor

IMG_6946.MOV

Testing the fourth sample

Sensor output (V) on the serial monitor in Arduino IDE, averaging 0.99 V

4. Conclusions

We found that the results ultimately aligned with our initial predictions: as the water got murkier and turbidity increased, the average voltage output on the serial monitor decreased.
- Clean water had the highest voltage output while being the clearest
- Muddy water had the lowest voltage output while being the murkiest

In this unit, I learned about water turbidity, basic analog vs. digital reads, and how to use the grove turbidity sensor on different types of water samples.
In general, there were a lot of varying reads for the turbidity sensor, so we tried to collect all of our data on the same day to ensure the most consistency.
Conventionally, clean water is less conductive than dirty water, meaning that electricity can't pass through it as easily; however, after testing out the sensors in this lab, it actually produced the opposite result.
- As turbidity increased (muddy), the voltage output actually decreased; as turbidity decreased (clear), the voltage output increased
- This was likely caused by an error in experimentation or faulty equipment.
In the future, I would try my best to avoid mixing or cross-contaminating different samples to make sure the results were as distinct as possible.

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