After connecting to the machine and entering the control page, users can see the web pages on their devices. The page consists of three main parts: temperature control, module switches, and data recording.
Temperature controlling
To limit the temperature to a certain range, we need a sensor to acquire the temperature and a heater to provide enough data needed. DS18B20 is chosen as the sensor. PTC (positive temperature coefficient) heaters are used because the resistance of PTC heaters rises as temperature goes up, and the current decreases, making it keep stable at a certain temperature. This is less likely to cause fire hazards caused by control failure compared with normal heating filaments.
Figure 1: PTC heaters.
Figure 2: PTC dress around a bottle.
The sensor is immersed in the fluid to get an accurate temperature. The sensor and wires are sealed in silicone rubber tubes to avoid damage of fluids to the sensor.
Figure 3: Temperature sensor sealed in silicone rubber tubes.
The program will detect the temperature and automatically switch on or off the relay connected to the heaters, limiting the temperature within a small range.
Figure 4: Temperature control on the web pages.
Modules
The machine is mainly a two-layer box made of Acrylic, whose 20cm wide inner layer is black to block light out, avoiding the impact from natural light. LED, mini pumps, and a stirrer were on the 30cm wide transparent outer layer. The NodeMCU controls some relays and further passes the control to the modules. Sensors are also connected to the Microcontroller, providing data on the conditions inside the box.
Figure 5: Multi-channel relay connected to NodeMCU.
The structure is highly extensible. The two-layer enables users to assemble modules at any position and hides the modules inside, providing both flexibility for maintainers and simplicity for users.
LED strips provide light to control the microbe. USB sockets can simplify the mounting and unmounting of different lights. There are UV LEDs for sterilization, blue lights, and red lights to provide conditions to control the microbes.
Figure 6: UV LEDs, blue LEDs, and red LED.
Three modules driven by motors are attached to the outer panel by screws. Extra holes on the outer layer make room for future extensions. A mini air pump, about 5cm long, aims to pump the air into the bottle and test the oxygen-controlled suicide switch. A mini peristaltic pump transfers the fluid, which will help add the microbe from one tube to the main bottle or transport the produce. A magnetic stirrer is at the bottom of the machine to speed up diffusion in the bottle. Sizes of the modules and length of screws are carefully chosen within the two-layer gap, keeping the simplicity of the machine's look from the outside.
Figure 7: Motors hidden in the two-layer structure: fluid pump(left), magnetic
stirrer(middle), air pump(right).
Users can control the modules by clicking the buttons on the webpage. States of modules refresh automatically for multi-user cases. The webpage provided by the machine is also flexible.
Figure 8: Buttons on the web page to control the modules.
Data acquisition
The data are shown on the web pages and refreshed automatically. Users can check or uncheck the 'auto record' button to decide whether proceed to record the data. Smartphones and computers have higher performance than the SoC in the machine. This recording function is implemented on the webpage, instead of the machine. Thus, users can fully take advantage of their devices connected to the box, without adding storage devices to it.
Figure 9: Data recorded by the web page.
Go back to the overview page
Acknowledgements
