"The BioBoard" is an Arduino-controlled sensor package that allow users to monitor a range of physiochemical factors related to microbiological processes (e.g. algae growing, youghurt production, kombucha fermentation, sourdough culturing, etc.) in liquid media/cultures, with real-time data transmission and graphic data visualization designed to make key correlations between these factors easily graspable.
Goals / Features
As a minimum, we want to be able to monitor temperature, pH and dissolved oxygen. We'd also like to be able to measure biomass, either directly or by proxy. The current plan is to build a thermometer, a dissolved oxygen sensor and a biomass probe ourselves, and supplementing with a commercial pH meter. Failing that, we'll buy a thermometer and an oxygen probe as well and attempt to hack them instead, and concentrate on standardising data protocols, building the supporting controller hardware and making the graphics look pretty.
Important considerations are affordability, accessibility and required precision. Biologically relevant temperature range is approx. 0-100°C; accuracy should not be less than ±0.5°C at 25-35°C. pH range is (1-14), and required precision is approx. ±0.5, preferably better. dO probe should be able to measure % conc. with an accuracy of approx. ±2%, preferably better. Biomass probe will likely be measuring absorbance as a proxy for total biomass, and can be validated using classic spectrophotometer and CFU count.
Digital Temperature Sensors (DTS)
- Avaliable as one-wire devices, use single digital pin
- Require no amplification or moderation to connect to Arduino
- Good precision in biological range
- ±0.5°C accuracy from –10°C to +85°C for DS1820
- Very cheap ($0.75 to $3.95)
- Comparatively limited temperature range
- –55°C to +125°C for DS1820
- -40°C to +125°C for TC1047A
- Accuracy only ±2°C for TC1047A at 25°C
- Sensitive to mechanical damage and liquid, so require protection/casing
- Single analog pin use
- Very cheap ($1.75 from Hacktronics)
- Comparatively limited temperature range (-40°C to +125°C)
- Accuracy approx. ±1°C at 25°C
- DS18B20 digital temperature sensor - $3.95 from Hacktronics
- TC1047A microchip - $0.60 from element14
- HANNA Instruments HI 98103 $55
- Milwaukee pH600 $20 - doesn't look like it needs specific buffers for calibration, but the accuracy is probably not great. Maybe it's enough, though.
- Google shopping results approx. $40 upwards
- SOTA pH Electrode $100 - expensive, but so so sweet: designed for continuous measurement, and comes with any kind of connector.
pH tester units
- Jenco 610 pH tester for $30 - perhaps it could be hacked?
- pHduino - Arduino-based pH-amplifier circuit for interfacing with a commercial pH probe.
- pH meter construction - this could perhaps be adapted to use an Arduino instead of a voltmeter - not necessarily cheaper than buying, although it’d certainly be both fun and informative.
Dissolved oxygen (DO) probes
Optode (a.k.a. build an intensity- or time-based optode from scratch)
Recently, people have been using a ruthenium complex as a visual (fluorescent) indicator of oxygen concentration. This complex is excited by a blue LED, then its transmission is measured by a filtered photoresistor (more details here in pdf)
- All solid state (super low maintenance)
- No calibration needed
- Could be some serious tecnical hurdles to overcome on this one
- Ru molecule is expensive (~$70/mg)
Film Contruction Ideas
- Disperse catalyst in PVC powder, bake in oven on top of PET film under compression. May hit a rheology problem with the PET film. Melting point of PET is close to that of PVC.
- Film coat: PVC dissolves in 2-butanone, whereas PET will not. Make a thin liquid layer, then allow to evaporate. PVC morphology may not provide necessary mechanical stiffness after this process.
- ruthenium complex
- DO-BTA Dissolved Oxygen Sensor $209
- Yellow Springs Dissolved Oxygen Meters $80-104
- Diagram for the construction of a lead-silver galvanic probe
- A discussion of the various types of dissolved oxygen probes from the Southern Regional Aquaculture Center. This article also contains a diagram of the typical polarographic sensor
- Currently lots of DIY spectroscopy projects under development
- Relatively easy build, can be made using a LED and a photoresistor, phototransistor, an old cell phone CCD or other simple photodetector
- Validation of results with known absorbance values should be easy
- Will likely need re-calibration for every use
- Could be very hard to pack into a probe
- ASD19-N Single Channel NIR Absorption Probe
- TruCell - NIR probe promotion PDF; basic intro to using spectrometry for biomass measurements, incl. calibration curves and equations
- Industrial application of NIR spectroscopy in fermentation and cell growth monitoring
- Cell phone spectrophotometer
- Article on how to build your own spectrophtometer
- DIY Spectrometer
- DIY Spectrometer FAQ - lots of useful links to other DIY spectro projects
A bare-bones Arduino set-up with USB connection to a dedicated lap-top initially; later - when we have more time for integration - an ethernet shield will be added to the assembly to give us wireless data transmission to the server.
Data logging and visualization
Data should be timestamped, categorized (pH, temperature, etc) and transmitted in real-time
- JSON data serialization format
- HTTP for transmission to server
- Include "export to CSV" function with option for data set selection - should allow people to use a variety of programming languages and data analysis tools without a lot of work on their part or ours
Custom Rails app
- Receives data
- Logs to database
- Generates graphs on demand
- Add Comet server for live-updated graphs
- Include 'export to CSV' function to allow users to extract data for analysis with tool(s)
- All code on github so others can fork and add features
- We could add features that lets new users sign up and get a unique key which they use when transmitting their own data to the JSON web service on our server. The server then uses the key to associate the data with the user, and the user can look at their graphs and share them with others.