The generic heating / cooling controller (hcctl) is a flexible bang-bang thermostat controller based on an ATTiny25.
The project has been expanded to accept a simple SPI temperature sensor. The test case uses a MAX31855 Cold-Junction Compensated Thermocouple-to-Digital Converter for K type thermocouples. The MAX31855 is around US$5 at Digikey for singles, but the tests were conducted using Adafruit MAX31855.
MAX31855
Thermocouples bring two challenges for hcctl:
- low noise amplification of very low sensor voltage;
- compensation of the ‘cold junction’ temperature; and
- high resolution ADC.
The MAX31855 provides a solution to all of these challenges in a single inexpensive chip. Continue reading SPI input for the generic heating / cooling controller