OpenTCC: An open source low-cost temperature-control chamber

Abstract

Microbial electrochemical technologies (MET) are emerging systems for environmental applications such as renewable energy production or pollution remediation. MET research often requires stable temperatures and low levels of electromagnetic interference. Due to the presence of electrical wires and sensors, heating MET using water jacket recirculation can raise safety issues, whereas heating coils may affect the results of electrochemical analyses. The proposed open-source temperature-control chamber (OpenTCC) aims to provide a low-cost solution for controlling temperature (in the range 20-55 °C) while simultaneously reducing the electromagnetic interferences caused by switching mode power supplies. OpenTCC consists of a light and cheap structure, incorporating eight heating pads and two Peltier-cooling modules powered by open-source electronic circuits. Its hardware is controlled by an Arduino microcontroller and a Python interface which provides data-logging and serve as a basis for programable temperature cycles. The system has a modular design to allow stacking several independent modules. OpenTCC provides a reliable and tunable temperature control at lower costs than currently available commercial temperature controllers and provides a platform for field-specific upgrades. Though optimized for MET, Open-TCC can be adapted to other laboratory applications due to its flexible design.

Keywords: Bioelectrochemistry; Electrical noise; Faraday cage; Incubator; Peltier element.

Graphical abstract

Fig. 1

Picture of the OpenTCC with incorporated old hard drives converted to magnetic stirrers (1), with brushless direct current (BLDC) motor driving electronics, and all the connections necessary for measuring and controlling electrode voltages in MET experiments (2). The image shows the temperature sensor AD22100 hanging from the top of the chamber (3) and the supplementary handheld thermometer (4).

Fig. 2

3D model of the OpenTCC that can be downloaded in format. fcstd and visualized using Freecad open source software. An additional. STEP file is provided for Autocad users.

Fig. 3

A) Detail of the installation of the Peltier thermoelectric modules. This can be downloaded from the /Schematics/structure. fcstd file on the repository of the project and visualized using Freecad open source software. B) Picture of the two Peltier modules installed at the back of OpenTCC.

Fig. 4

Circuit schematic for the Pt-100 temperature meter. Wheatstone bridge and instrumentation amplifier to obtain voltage differences between the reference voltage (between R w1 and R w2) and the divider (between RTD and R w3). The voltage difference is amplified by an instrumentation amplifier consisting of 3 op-amps to obtain a signal read on the analog input of the Arduino (A). Picture of the circuit designed for environmental temperature monitoring with two double op-amp ICs (B).

Fig. 5

Connections required to obtained temperature measurements from the AD22100.

Fig. 6

Schematics of the connections required to combine the switching control signals of the Arduino with the ATX power supply and heating/cooling modules (A). Two optocouplers isolated the Arduino circuitry from the MOSFET and power supply circuit. Limiting resistors were placed for the indicator LEDs. A flyback Schottky diode was placed across the fans to avoid inductive spikes during on/off operation. Pull-down resistors were placed at each of the MOSFET gates to avoid half-opened gates. Picture of the switching power circuitry box (B).

Fig. 7

Screenshot of the OpenTCC in operation. The phyton graphical user interface [A] shows the readings for internal and external temperature from the Arduino and allow to set the internal temperature by clicking in “New temperature”. The python program is run from the command line [B] where serial information serves for error handling. The python program creates a folder [C] and records the information from the Arduino in a new file each day, with related timestamps for posterior data analysis [D].

Fig. 8

Time required to achieve the set temperature of 20 (A), 30 (B), 40 (C) or 55 °C (D) from different initial temperatures (20, 30, 40 or 55 °C). Data was plotted applying R programming scripts to the raw data obtained from the PySerial_loop programs (repository: Plotting).

Fig. 9

Long-term (60 h) temperature control inside OpenTCC at 20 °C (A) or 50 °C (C) with the respective magnifications (B, D). Temperatures were registered inside (red) and outside (green) the chamber at 5 s intervals. The temperature inside the chamber shows steps between the temperature values corresponding to the data conversion of the temperature sensor around the hysteresis of the Arduino. Data was plotted applying R programming scripts to the raw data obtained from the PySerial_GUI program (OSF repository: Plotting). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 10

Electromagnetic interference (EMI) inside and outside OpenTCC. Plot A shows the frequencies rejected by the aluminium structure of OpenTCC between 30 and 35 kHz and 60–70 kHz. Plot B shows that the mains noise (50–60 Hz) is slightly dampened, but still present inside the OpenTCC. The plots were obtained by collecting screenshots from the Linux version of Aaronia Spectrum Analyzer software and cleaning and placing up the figures with GIMP software.