Around the ThermoClock: A precision automated temperature control system for Ex Vivo circadian studies

Temperature treatment is commonly used to manipulate circadian rhythms in cells and tissue cultures. However, it is often laborious and error-prone in prolonged studies. We present the ThermoClock, an Arduino-based temperature regulation system designed for precise, automated temperature control in ex vivo and in vitro studies, particularly circadian rhythm research. Built with off-the-shelf components and open-source software, ThermoClock is easy to fabricate, costing approximately $450 and requiring under 10 h to assemble. Its modular design enables simultaneous control of multiple conditions, reducing manual intervention and user error. Individual ThermoClock modules use a Proportional-Integral-Derivative (PID) controller and off-the-shelf electronics to realize real time, precise temperature controls, while being cost-friendly and accessible to construct and operate. Assembled ThermoClock can operate up to five temperature modules, greatly enhancing experimental versatility and throughput. An Arduino script is provided to automate the temperature controls based on user-input temperature setpoint schedules. ThermoClock is designed to function in an incubator and shows significantly faster heating and cooling (p < 0.001) compared to a programmable incubator. It reaches the target temperature within five minutes after a setpoint change.