Making a smart thermostat, smarter

I had already conceived a smarter thermostat in a DIY project utilizing the Cool, Heat and Fan controlling circuitry creatively to provide a more even and economical distribution of my HVAC system. Even though I already had a C wire hookup to support a centrally powered unit, my DIY approaches were always clunky looking and lacked aesthetic appeal to be located at the front entrance to my condo. I already had the opto-isolators and triacs to implement nice solid-state-relays to avoid mechanical relays, but especially painful was trying to hide the buck converter from 24vac to 5vdc for my processor of choice, the ESP32S3. The specs were simple....

1. No display, only remote control depicting "I'm warm or I'm cool" via phone interface or Alexa voice control

2. Integral inside temp sensing with the ability of remote room sensors

3. Internet access to retrieve outdoor weather conditions.

4. Integral geofencing to determine at home presence

5. NTP access to get time and date info for scheduling, if I choose.

Then came Amazon Prime Day! Their Wifi Smart thermostat made by Honeywell was bring offered for $50 ($30 off list)! It was an attractive unit. Very simple and had the Alexa interface built in, obviously. I ordered it immediately and received the unit the next day. Installation was as simple as the many videos and Alexa coaching illustrated, but the hidden surprises were just being revealed.

The first disappointment was the fact that the unit's temperature display could not be calibrated. My existing Honeywell thermostat allowed me to "calibrate" the display to show 3 degrees lower than it measured. That is a big psychological factor, especially with my wife... I always set the thermostat to be a comfortable temperature at the point where we sit and that is not at 5 feet above the floor at the front door. To resolve this I wanted to implement spec #1... No display.

The best feature was the fact I could control not only the temperature and fan via Alexa routines, but also the active and inactive display brightness! I could turn the display off! Spec #1 check!

The second surprise I learned is that the thermostat provided a circulate mode where the fan would periodically come on to even out the AC and avoid the sudden blast of cold air when it kicked on. This is exactly what I had planned in my DIY design. This was a nice surprise indeed.

I have to mention that these features are never discussed in the reviews or descriptions of the unit. I hope your imagination for the possibilities is starting to peak, as mine did.

The unit does not have the ability to have remote temperature/humidity sensors or geofencing, but Alas! I have my ESP32S3 all polished up and ready to take on the tasks planned for my DIY thermostat. On top of that, I could locate it where I wanted the temperature to be sensed (near my TV chair LOL). I eventually settled on using an S2 that I had in my drawer only because with the native usb and no bluetooth, it was ideal for this no-brainer task (and little else), but any ESP32 would work. I often debug my code using an esp32 dev board with an integrated serial that is consistent with the multiple resets and reprogramming. The scripts are pretty simple and as usual I do everything using the Arduino IDE. As with all my devices, I add Arduino OTA, so the lack of a serial chip quickly becomes moot.

I've built and programmed many sensor and Alexa controlled devices and utilize two main services/libraries to give me full closed loop control. The first is the fauxmoESP library which provides for an Alexa controlled device on my network and secondly I use www.virtualsmarthome.xyz which proves the ability to trigger Alexa routines via a url from my devices. Both of these, at the time of writing this, are free of charge, but a donation to their cause is always appropriate once you see their uses.

The third service I use regularly is callmebot.com. It provides for alert messaging through WhatsApp, which I use a lot having extended family across Europe. I initially used SMS messaging though the email gateways for AT&T and T-mobile, but they proved untimely and unreliable. Callmebot.com offers their service for free, but for $4 per year option, the service is invaluable for immediate alert messaging. I use them now all over my projects, not just the thermostat,

So that's the story. Having all the components in hand it was all left to my imagination to implement my "Smarter" thermostat.