Fermentation controller

Projects
Participants	Algoldor, Justa
Skills	electronics, Biology, Brewing, Coding, Construction, Making, Open source projects, PCB Design, UI design
Status	Planning
Niche	Electronics
Purpose	Fun

Outline

The fermentation controller has been a longstanding item on the wishlist of Fermentation-god Frantisek Apfelbeck of Noisebridge fame. The goal is to have a simple to construct device that will manage fermenting a number of products; managing the aspects involved such as temperature control, timing, etc.

One of the specific goals is to implement one that supports heat-cycles where one keeps the fermentation-batch at different temperatures for periods of time to ensure that, in a multi-species culture, each species will have a time for optimal growth.

Other aims are to ensure easy construction , safe operation and ease-of-use.

Basic requirements

The device is primarly engaged in timing and controling temperature within a preferably insulated enclosed space containing a batch of liquid. Direct heating and/or cooling of liquid is assumed but perhaps not guaranteed.

The operation of the device should be field-adjustable. As such it requires a way of providing feed-back on the device and allowing for input of parameters or adjustments of settings.

It would be good to have a way of storing presets on the device for easy re-use, as well as preservation of operational settings during power-down.

Since the device is involved with controlling temperature , it requires both a device to measure temperature as well as a device to control it. For our current purposes, it is assumed that keeping the temperature high enough is the basic design challenge, but optional cooling-devices should be kept in mind as well.

Given that the heating of larger batches of liquids might well involve greater amounts of power than is easily feasible through low-voltage devices, the need for a safe way to drive HVAC currents might be introduced.

Since the device involves controlling temperature in 'cycles' , it is obvious it will require an accurate way to time it's operation. Since the device could concievably undergo power-cuts due to deployment on renewable and unreliable power-sources such as solar or wind-power. Having the device 'forget' how far it is into it's operation would mean an almost guaranteed failure of the fermentation-batch.

With the above in mind; the device could concretely consist of:

• A microcontroller with enough IO for driving the below peripherals as well as internal or external eeprom-memory for storing settings/presets.
• A/some temperature-measurement peripheral(s)
• A display device of some kind with accompanying set of inputs.
  • A graphical LCD or character LCD
  • A set of buttons in cursor-layout and/or rotary encoders or joystick could all serve as inputs
  • Alternatively; one could replace or augment the onboard input/output through means of using an existing and commonly available communication-device as input/settings controller and display. Think smartphone + Bluetooth/wifi
• A way to heat things; preferably liquids. Immersion-heaters come to mind. Either 12V or 110/220VAC should be considered; keeping options open for easy adjustment of existing design to fit specific needs
• An option to add a cooling device. Either through the means of air-displacement and/or evaporation, or more brute-force approaches such as peltier and/or refrigeration-units.
• An immersible, rugged and food-safe way to measure the temperature of a gas, liquid or perhaps solid attached to the fermentation-product. It should be able to survive the usual range of temperatures from -20 to +100 or so, and be accurate within the range of 5 to 50 degrees celsius.
• Unless realized through means of battery-backup and brown-out protection, the device might benefit greatly from having a small dedicated-purpose battery-assisted real-time-clock module onboard to preserve the device's sense of time.

Basic prototype

With the above requirements in mind and the wish to have a platform that's easy for me and others to develop/prototype for, I have chosen to take the basic 'Everything is an arduino, unless specified otherwise' approach. Using that guideline, it becomes easy to have whole sections of the hardware-requirements covered with full support in the development-environment used. Arduino has a large number of well-supported peripherals available to it, despite it's further flaws. Also, the arduino environment and language is well understood by many , making it easy to find references and assistance when stuck on a particular part of things.

Given that the Arduino is basically an AVR Atmega168/328 with some power-select logic and , often, a USB->Serial convertor onboard, the choice of further peripherals must come with a number of considerations in mind:

• They preferably use 5Volts as a working voltage
• They interface through one of the available buses on the AVR; SPI, I2C or even serial.
• The perhaps come in easily acquired pre-made 'shields' available for the Arduino, if at a cost low enough to warrant not simply making one yourself.
• The AVR has the benefit of containing built-in EEPROM memory, usable for storing settings/etc.

Parts for my current 'working draft prototype' have been ordered and shipped by now and should be underway. Most of them have been acquired through [DealeXtreme] An overview of the parts I intend to use:

• [Some Arduino Board ] Approx $15
• [An LCD and Keypad shield for Arduino ] $6.90 A real bargain given that it solves user interaction in one fell swoop.
• [An Arduino prototyping shield] $2.30 Makes for easy interfacing to Arduino IO-pins and add extra onboard peripherals as well as connectors to off-board devices.
• [An DS18B20-based temperature probe] $5.90 Not cheap, but totally foolproof to work with. Great for first prototypes, can later be retooled into calibrated PT100 setup or otherwise.
• [A solid-state relay for HVAC] $6.70 These make safely interfacing with HVAC a problem that anyone can easily and safely implement; taking the pain out of having to do your own opto-isolation and creating a seperate PSU for the isolated HVAC-related switching circuit.
• [An RTC (real-time-clock) module based on the DS1302] $3.60 Battery-backuped, precise, cheap. Comes with an extra 31x8 bits of backuped RAM; perhaps saving the EEPROM-flash from getting written too often. Yet to be purchased, however.
• Various and miscellaneous bits of hardware; think plugs, sockets, powercords, wire-terminals, pinstrips, resistors, diodes, etc. Perhaps MOS-FET for driving fan or other low-voltage peripherals.