Requirements

Before I get too far down the road, I need to establish some high level specs.
The end product will:

• measure incoming water temperature (EWT)
• measure outgoing water temperature (OWT)
• measure return air temperature
• measure supply air temperature
• measure supply humidity
• measure outside temperature
• log the data somewhere somehow
• display the data on an LCD (of course)

It will be nice to have:

• measure KWh usage for whole house 
• measure KWh usage for HVAC
• pulse monitor for water meter (have one sitting in the closet)
• keep track of seconds the burner in the water heater is running
• RTC for data tagging

Devices:

• DS18S20 temperature sensor (few in the drawer)
• PIC16C84 (if we cannot smash the code in there, we will buy a bigger one)
• HSU-07 humidity sensor
• 16x20 LCD (need a good cheap source)
• Bluetooth serial module (these ain't the dark times with cables and stuff)
• 433MHz wireless modules (just in case)
• 74HC138 will slim down the 1-wire
• Flame sensor - Cool!

Misc:

• Google for data logging
• DesignSpark for PCB creation (seriously, I tried Eagle and could not figure it out).

Going Geothermal

In December of 2010, I finally made the decision to replace my aging HVAC and update it to a vertical closed loop geothermal system (Yes, it was expensive.  But, it was the right thing today and I wish more people would made decisions based on the future and not the hear and now).  While researching geothermal, I ran across individuals using Web Energy Logger to monitor their home ecosystems. For the longest time, I watched this house up in Plano and was been envious of not only the monstrous floor plan, but of the kick ass WEL monitoring system that is installed.  This simple event rekindled my interest in the PIC microcontroller and dusting off my BSEE (paper only).

Back in the mid 90's, while I was working at a small engineering company in Austin, TX, I spent an entire summer designing small control modules with the legendary PIC16C54 and PIC16C71.  Wow!  Things sure have changed.  Back then there were few alternatives (enjoyable) to PICs and they were quite the fan fair.  Today, the playing field is a tight battle among Microchip PIC, Atmel AVR and the TI MSP430 series of microprocessors.  With my rediscovered interest in microcontrollers (and being off the scene for so long, I figured I would dabble in each of them a bit).  Rather than bother with that story, let's just say old habits die hard (you always retreat to what you know).

If you are interested (if not skip on), this basically sums up my decision to stick with the PIC.

• I already know PIC assembly (but that ain't hard and I have no intention of using it)
• Free C compilers are available for all of them
• I don't use a Mac or Linux, so those are not driving factors
• The prices are about the same
• The MSP430 is too modern at 3.3V
• I already had a PIC programmer and two PIC16C84s laying around (yea, I typed 'C')

In all honesty, if I were to start all over, I would have picked the AVR, just for the social popularity.  But, here we are and here we go.