### Build a Turbidity Sensor to Monitor and Control Microalgae Biomass Density

#### Parts needed

1. A turbidity sensor like this one in the photo below. The one in the listing has an open passage, so I have to buy another one with a close passage. The open passage can be to submerge the sensor directly to the reactor. An op-amp breakout such as this one (comes with an open channel turbidity sensor)make increase the gain of signal.
2. An Arduino board. It could be Nano, or Mega/Uno (if Yun Shield is used)
3. A potentiometer. Better to use the precision one from the link.
4. An OLED screen. I used SSD1306, but other types of LCD such as 16x02, 20x04 would work (and revise the code accordingly).
5. A replay board with two channels like this
6. Two of three-position switches for additional manual control
7. Pumps: I bought a 12V small peristaltic pump , and used a Cole Parmer dual channel pump in the lab as the main pump. If the main pump only has one channel head, then use the overflow tube to collect the surplus biomass, beware that a possible skimming of biomass on the top of the reactor if you are using a vigorous airlift mixing.
8. A Raspberry Pi or a laptop to log data for Option 2 or a Yun Shield for Option 1
9. My first implementation is with Option 1: Using Yun Shield to provide a timestamp, internet connect, and data storage with a microSD card. The Yun Shield is similar to Arduino Yun, using a minimal Linux (OpenWRT) on top of Atmel chip. Yun Shield is designed to as the same form factor as Arduino UNO/Mega. Using the Raspberry Pi (RPi) as Option 2 cames later. The cost of Yun Shield and RPi is almost the same ($35, 2018). For Option 2, data from Arduino UNO/Mega is captured by a Python script run on RPi. A full-fledged Linux distro on RPi with 40 GPIO (general-purpose input output) pins is potential to develop a stand-alone system. The total cost is in the range of$200. The Cole Parmer pump alone ranges about \$1000, and not included in the total cost. I did not make an exact summation.