Data Logger Collecting Temperature, pH and Dissolved Oxygen with Timestamp
- Make a data logger for less than $500. The logger can store data for the temperature, pH and Disoled Oxygen with a time stamp and using I2C communication.
- Why I2C (Inter-Integrated Circuit) communication mode? The main reason is one microcontroller can stack up (daisy-chained) as many sensors with two wires given that each sensor/client has an unique address.
1. Parts needed
This data logger is specfic to the need I have with a photobioreactor culturing microalgae. Culturing microalgae needs several key parameters in which the temperature is for thermo control and biological status, pH is for CO2 supply and control, and Dissolved Oxygen (DO) is for photosynthesis activity. This data logger can be used for other biological systems such as with aerating or pH static control.
are microscopic algae, found in fresh water and marine environments. Their size ranges from a few micrometers to a few hundred micrometers. Their function to the Earth system is similar to the plants that is, to convert solar energy to reduce carbon dioxde to organic carbon. This is vital to the Earth. Converting photon energy to chemical-bond energy is the first step to keep the solar energy in Earth. The oldest form of microalgae dated back 3-4 billion years ago. Together, the microalgae produce a half of the atmospheric oxygen (according to Wikipedia.)
Microalage in Industry Context
One disadvantage of microalgae in compare with solar photovoltaics is a much lower efficiency in converting solar energy to equipvalent energy either in term of chemical bond or in electron potential. Comparing effiency in energy context favors the photovoltaics to electricity conversion. The argument for microalage is a neutral-carbon process or zero generation of new carbon dioxide in contrast to fossil fuels. The carbon atoms acted as electron carriers collecting electron during photosynthesis and releasing those to oxygen during combustion. Meanwhile, burning fossil fuels releases carbon dioxide to the atmostpher and thickens a layer of greenhouse gases. The microalga biomass after harvest is extracted for liquid fuel to displace some percentage of fossil fuels. The value of microalgae is the type of compounds they produced and not merely by the energy they harvested.Source: https://www.cosia.ca/initiatives/greenhouse-gases/projects/algae-project
What the hell to do with this data logger?
Microalgae needs CO2 as the building block or the material to dump electrons splitted from water. Before the photosysnthesis happens, the oxidation potential of carbon in carbon dioxide is plus 4 (+4), which means the carbon atoms is stripped away the electrons. Carbon dioxide is a stable gas because both carbon and oxygen atoms are at their lower energy status.
Photosynthesis happens in two main stages:
After one round of photosynthesis, CO2 molecules are consumed which leads to a tiny increment of the pH. If the reaction happens for a long time, most bio-available forms of inorganic carbons are exhauted and slows down the reaction rate. Now, I need to build a system to automatically replensishing CO2 just enough; otherwise, the pH is too low for the microalgae that effects functional groups on the cell's membrane. Balancing the CO2 can be done by installing an in-situ pH probe and reading the pH value to turn on/turn of a solonoid valve. When the solonoid valve is open, the CO2 is injected and dissolved in the microalgae culture and that reduces the pH of water. In the mean time, energy light from LEDs or from the Sun heats up the reactor. For research and improvement, retrieving the data DO, pH, and temperature with a high resolution (minute scale) would help to reconstruct what has happened. For the photosysnthesis of microalgae, replacing the plant in the reaction below for microalage, and submerse the reaction into water. That is what happening in the microalgae culture.
Podcast >>> Algae: Food, Fuel or What?
Stuff You Should Know podcast, one of my favorite recently made one for microalgae, take a listen: Algae: Food, Fuel, What?
Gallery of the parts
Lists of parts with the price (2017):
- Arduino MEGA 2560, $35, https://goo.gl/6EdBGu
- Power adapter for Arduino board, $5.98, https://goo.gl/BzuZbk
- LCD module I2C (display), $8.99, https://goo.gl/za3cBn
- Real-Time Clock (RTC) breakout, $7.5, https://www.adafruit.com/product/3296
- MicroSD card breakout board, $7.5, https://www.adafruit.com/product/254
- 4GB SD card, $6.98, https://goo.gl/tCY2ys
- Waterproof DS18B20 Digital sensor, $9.95, https://www.adafruit.com/product/381
- pH probe + Kits+ Standard buffers, $149.15, https://www.atlas-scientific.com/product_pages/kit...
- DO probe + Kits+ Standard buffers, $247.45, https://www.atlas-scientific.com/product_pages/kit...
- Breadboard, jumper cable, $7.98, https://goo.gl/3g3mTe
- (Optional) Voltage Isolator, $24, https://www.atlas-scientific.com/product_pages/cir...
- (Update) Voltage Isolator with USB connector, $50, Voltage Insolator with USB port.
As of September 2018, the Atlas-Scientific has updated the design of the insolator. The pH/DO breakout can be plugged on top the insolator. The USB port is convenenient for a advance setup such as with Raspberry Pi.
In addition, the isolation of water is much less in air. The voltage insolator is not cheap, but it worths to invest and reduces the headache later.
- The price was updated on 2017, slightly changed in September 2018. The DO and pH probes contribute to the major of the total cost. A simple data logger to collect only temperature could cost less $20.
- Certain parts (like the generic board: Arduino, temperature sensors) can be bought from other vendors (Aliexpress, eBay, Chinese seller) for a lower price. pH and DO probes are recommended to get them from Atlas Scientific or other trusted vendors.
- A multimeter is recommended to check conductivity and voltage. It costs about $10-15 (https://goo.gl/iAMDJo)
Links above are for a reference. I do not affiliate for any of the vendors.