"The BioBoard" is an Arduino-controlled sensor package that allowusers 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 wireless 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.
- Very robust, good for nasty environments
- Wide temperature range (−200°C to +1350°C for type K)
- Relatively cheap (approx. $15 for a DIY model incl. amplifier)
- Voltage is very small so requires an amplifier with digital out (41 µV/°C for type K)
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
- Hollow Tube Thermocouple Probe - $19 from Omega
- both wires in a sheath ~$1/foot, by the foot from McMaster Carr
- Omega bare wire is here. Omega is the ultimate source, but they seem to only sell it by the roll (25 foot minimum, buy both wires separately) or in the form of super nice manufactured probes ($)
- TC amplifier - $12 from Sparkfun
- DS18B20 digital temperature sensor - $3.95 from Hacktronics
- TC1047A microchip - $0.60 from element14
- Charlie has access to a good amount of Type K metal sheathed TC wire, plus assorted probes and a TC reader he can donate - as we go along our improving expertise will lead us to resources other people can use... like the relatively cheap McMaster Carr wire.
- We presently have a not-quite-functional prototype digital thermometer which uses a DS18B20 DTS; the sketch is compiling correctly, but there's de-bugging to be done (error msg reads: avrdude: stk500_getsync(): not in sync: resp=0x31).
- Instructable for how to build a thermocouple. This soldering method will work with the Omega wire, and better junctions can be made with a welder or capacitive discharge.
- USB Thermocouple Project
- 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?
- 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.
- We could also build this
Dissolved oxygen (DO) probes
Membrane electrode (a.k.a. strip an automotive O2 sensor for parts to make a membrane electrode)
- New sensors for out of date cars are available on eBay for $10
- Contain required platinum, anodes, and teflon membrane
- Sensors typically operate at ~300C
- Ordered 3 $6-$10 probes on ebay to futz with
- Plan is to knock out the zirconium matrix and add a KCl electrolyte to see if we can get a reaction started at room temperature.
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)
- ruthenium complex
- DO-BTA Dissolved Oxygen Sensor $209
- Yellow Springs Dissolved Oxygen Meters $80-104
- Currently lots of DIY spectroscopy projects under development
- Relatively easy build, can be made using a LED and an old cell phone CCD
- Can be used for chemical analysis as well
- Verification of results with known absorbance values should be easy
- Will likely need re-calibration for every use
- Also a spectroscopy technique, so as above
- Tried and tested method
- Re-calibration needed every time
Calibrated capacitance + conductivity sensor
Industry has commercial probes available which measure living biomass; we think we may be able to retroengineer such a thing. With enough calibration, it might be possible to do this by measuring capacitance alone.
[The basic principle behind these probes is the different electrical properties of living and dead cells; both are conductive - being essential very long and folded chains of carbon molecules - but living cells also act as capacitors (batteries); active transport across the cell membrane of electrically charged ions/molecules establishes a negative potential/charge on the order of -70mV in resting mammalian neurons.]
- [finesse.com/files/pdfs/app-tech-notes/TruCell.TN.AUvsOD.pdf .pdf with technical notes about a commercial OD probe]
- Industrial application of NIR spectroscopy in fermentation and cell growth monitoring
- Cell phone spectrophotometer
Arduino is the microcontroller of choice; which board will depend on which assembly we choose.
Ethernet shield set-up
- Cheap and simple
- Perhaps not enough power + pins for sensors
Sensor shield + biffer board set-up
- More power + pins for sensors
- The biffer board is excellent and tiny (1W)
- No experience with use of the sensor shield
- More parts = more $
- More parts also = more work + more potential complications
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.