Freezer / Incubator
This page describes how to build a freezer/incubator using a thermoelectric device. The thermoelectric device creates a temperature gradient: cooling or heating the interior of a container relative to the outside air. We place it between two heatsinks with fans to improve the heating and cooling.
- In open air, it can refrigerate the contents.
- Inside a refrigerator, it can freeze the contents.
- Inside a household freezer, it can provide a consistent -20°C, useful for storing biological compounds.
- By reversing the polarity of the thermoelectric device, you can use it as an incubator (for example, for petri dish cultures).
Beyond aiding lab work, the system provides a chance to learn about feedback loops and basic control theory.
- foam cooler
- thermoelectric device (from sparkfun)
- heat sink grease (from newegg)
- two heat sinks with fans (from newegg)
- zip tie (6 to 8")
- 12V power supply
- barrel connector adapter
- Arduino Uno
- Grove shield
- temperature probe
- OLED display
- Grove wires
- short red wire
- hot glue
- double-sided foam tape
- Cut a hole in the foam cooler for the heat sink stack. Use one of the heat sinks as a guide.
- Place the thermoelectric device between the heat sinks. Apply heat sink grease if the heat sinks don't already have it.
- Secure the heat sinks using a zip tie.
- Connect the black wires from the fans and thermoelectric device to the negative side of the barrel connector.
- Connect the red wire from the thermoelectric device to one side of the relay.
- Connect the short red jumper wire from the other side of the relay to the positive side of the barrel connector.
- Also connect the red wires from the fan to the positive side of the barrel connector.
- Place the Grove shield on the Arduino.
- Connect the relay to D8.
- Connect the temperature probe to D4.
- Connect the potentiometer to A0.
- Connect the OLED display to an I2C pin.
- Use a drill bit to create a hole (slightly undersized) in the foam cooler for the temperature probe.
- Place the heat sink stack and temperature probe into the foam cooler. If desired, secure them with hot glue.
- Use double-sided tape to hold the relay and OLED display.
- Create a data flow for the Arduino.
- What is the largest temperature difference you can obtain with your thermoelectric device?
- Is the amount of cooling different when starting at a lower temperature?
- How much of a difference is made by running the fans?
- How often does the relay switch when running the data flow?
- What improvements would you make to the data flow rules?