How does it work?
The fermenter is composed of a small fan, a heating pad, an electronic board with a micro-controller, a screen and a button, and a temperature sensor. The sensor measures the temperature in the fermenter, the heating pad produces heat in exchange for electricity and the fan spreads it evenly. The interface (screen, button) allows the selection of the ideal temperature for the desired fermentation and the programming of a timer.
The printed circuit board (PCB)
After several prototypes were made in Fab Lab Barcelona using a Roland SRM-20 mini milling machine and a single-sided PCB, we finally decided to go one step further and reduce the size of our PCB by designing a two-sided PCB to better fit the design of our fermenter. The PCB is now designed in Fusion360 and produced by a PCB manufacturer. Below are the schematic and manufacturing files.
Schematics
PCB design
The PCB was designed with the following constraints in mind:
- The display, rotary encoder and RGB LED on the top side, all other components on the other side. This is to facilitate assembly, which can be done later by a pick and place machine.
- The USB port of the Raspberry Pico is oriented to the right. This allows easy access once assembled in the cabinet for any updates.
- Connectors for the power supply, fan, heating pad and sensor at the front. This allows easy access to connect and disconnect inputs/outputs as required, even when fully assembled.
List of components
- Domingo Fermenter PCB
- Raspberry Pico
- Fan 12V
- Heating Pad
- Temperature sensor (MCP9808)
- OLED display
- Rotary encoder
- Power jack with switch
- Sensor connector
- Sensor cable
- JST 2-pin cables (3x)
- JST 2-pin connectors (3x)
- Voltage regulator
- Capacitor 10uF (2x)
- LED RGB
- Resistor 220R (3x)
- Resistor 10K (4x)
- MOSFET (2x)
- Diode
- Power supply 12V 2A
Assembly
Soldering tips and tricks
- We find it easiest to start soldering the small components on the back side (where the Domingo logo is) so you can keep the PCB flat on your work surface.
- The diode has a direction and therefore a line painted on its packaging. It indicates the ground. It goes to the side of the longest line seen on the PCB.
- The connectors have legs on both sides that must be soldered as well to strengthen the components in place. Especially because they will receive forces when connecting and disconnecting cables.
- The direction of the Raspberry Pico can be seen from the small rectangle on the PCB indicating the Pico’s USB port. Solder it accordingly.
- The RGB LED ground leg can be identified by the white dot printed on the PCB.
Connections
- The JST-2Pin connectors are placed so that the 12V line is on the right pin and the GND line on the left pin. Make your cable accordingly.
- The sensor cable comes ready to use, so no potential mistakes here.
Software
The fermenter software is written in MicroPython so that the code is relatively easy for anyone to read and is also designed to be taught in workshops.