After showing how to connect the LCD Touchscreen from adafruit in Part 5 for this Java SE Embedded thermostat project, I figured out a simpler solution for the relays needed to turn on and off the furnace, fan, and A/C of a home heating and cooling system (just like the Nest thermostat).
So, it's time to show how to do a time-honored tradition in high tech start-up prototyping: Refactoring.
I found this cool Single Relay Board from Parallax. It can control up to 120VAC at 10 amps, but we only need to control 24VAC 1 amp relays for the home furnace, fan, and A/C. And most importantly, this Single Relay Board can take a 3.3 VDC signal from a microcontroller or Raspberry Pi running the Java SE Embedded platform (like we are doing in the project). No need for SPI or i2c, just a straight GPIO high value (3.3VDC) from the Raspberry Pi header pins from a Java SE Embedded app will control the relays. Cool!
So, I've got a bit of refactoring to do of my previous blog posts to swap in 3 of these Single Relay Boards (go ahead and order 3 if you are playing along at home). But, it's all good. Refactoring is part of the process of high tech start-up prototyping, right? :-)
Full series of steps: