Turbidity Sensor

This turbidity sensor is specially designed for the course ‘Measurements for water’ given by Delft University of Technology. In this manual, we will explain how you can build your own turbidity sensor.

We are going to build a sensor that can measure the amount of light that shines through a sample to determine the turbidity of the sample. If the sample has a high turbidity the amount of light from the laser that reaches the sensor will be lower. So, the LDR sensor will be measuring the difference in light intensity that shines on the sensor.

A list of all things needed to build the sensor:

Electronics:

· Particle Photon

· Breadboard

· LDR-sensor

· Resistors

· LED’s

· Wires

· USB Micro B cable

· Push button

· Laser

Setup:

· Box

· Duct tape

· Wooden blocks

· Square glass

· Black paint

Tools:

· Soldering iron

· Wire cutters and strippers

· Knife

The first thing that’s need to be done is the setting up the electronics. We will be working with a Particle Photon and a breadboard. When the Photon is all setup and connected with the internet, the wires and the sensors can be installed. In the picture the schematics of the breadboard can be seen. The setup can be adopted equally as seen in the picture. We used a button to start the measurements and a LED to indicate us if the Photon is measuring.

The code that can be used for driving the sensor can be found below. It measures the light intensity from the laser on the LDR sensor when the button is pressed. A light will flash constantly if the button is pressed and measurements are being done by the Particle Photon.

Description of the code

In the picture you see the programmed code that we have written for our sensor. In the first part you see the description of what is plugged in, in which pin. In the second part, the void setup, we tell the photon that the LED is an output and the LDR and pushbutton are inputs. In the last part, the void loop, we say that if the pushbutton is pressed down the photon has to take a measurement every second of the LDR and convert that into an percentage of light that has been transmitted. This value (of the LDR) and percentage are published to the particle cloud. If the pushbutton is not pressed down, the LED will blink and nothing is measured.

The setup is quite simple. We are going to build a setup that will be placed in a box. The box will prevent, that light from the surrounding will be shining on the LDR sensor, so that the measurements will be more accurate. We used a simple shoebox, which we painted black. A sample in a small glass can be placed between the laser and the sensor. Wooden blocks are used to lift the laser to the same height as the LDR (these heights have to be measured and be the same). Depending on which glass used, the laser may be bended by the angle of the glass. The use of a glass with straight walls may prevent this. The push button en LED are placed outside the box, so you are able to start measuring when te box is closed.