Abstract
A simple temperature control system constructed from a $10 homemade, precise, solid-state, proportional thermoregulator, resistive heating element, and insulated enclosure is described. It is intended as one of a series of small heated units, each set to a different temperature and placed in a single, large, refrigerated area, such as a large cooler or air-conditioned room, but can be modified for cooling in a heated area. Its demonstrated temperature control precision over 24 hr was ± 0.02°C at the thermal sensor at a set point of 25° and ambient of 19° ± 2.5°. Control temperature precision, range, and span are determined by thermoregulator components, enclosure construction, and ambient conditions. This or similar systems have been used successfully in seed germination, postharvest, cell culture, and nutrient release studies.