The next part of my project is focused on reading the CO senor. The CO sensor I am using is the Hanwei MQ7 (data sheet: https://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-7.pdf).

The CO sensor requires a 5v power supply that may be provided with a 5v fixed regulator or the 5v pin of the micro-controller. The more difficult part to control is the heater element that requires a shifting voltage to toggle between 1.4v and 5v. Fairchild semiconductor makes a Adjustable/Fixed voltage regulator that is a fixed 5 volts when no controller resistor is hooked up to the control pin and between 1.25v and 32v when the resistor is active on the control pin. By using a solid state relay we can isolate the adjustment pin of the regulator to provide our 5 volts when the relay is open and 1.4 volts when the relay is closed and connected to the the proper resistance value. I just used a 50k trim pot to speed the implemenaation up.