Relatively simple in concept, this was a 3 channel comparator system based on one or two remote LM35 temperature sensors placed in the growth chamber, and two remote precision linear potentiometers mounted on the front panel . For simple chambers – those without the CMP3000 control system – it would function as a simple heat and/or cool controller.
For larger systems, it replaced the electro-mechanical failsafe alarm/shutdown system, providing an accurate, repeatable, easily settable minimum and/or maximum limit for chamber temperature.
It was a fairly simple circuit, but had to accomplish its task with only a single supply, single ended comparator chips, and one circuit board for multiple configurations. The system was designed to be fail-safe in the event of a sensor malfunction or open pot. There were configurations where its range was -30C to +30C, and others where it was +10C to +70C.
This product taught me straight analog circuitry, summing notes, differential nodes, analog hysterisis, fail-safe operation, and chatter reduction. Pretty cool for a fairly simple circuit!