Taking Apart the WiFi Honeywell Thermostat

Written 2016-08-02

Tags:Honeywell Atmel Atmega 

I have another thermostat

It was made by Honeywell, and I found it at the store. This one uses WiFi and is pin-compatible with my existing one.


What is in the box?

Another Box


What is inside?

One assembled thermostat, front


One assembled thermostat, back


We can see three subsection of the device. In the center is the umbilical to the home. On the left is the WiFi section. The rest of the PCB is covered by the frame.

What is under panel number one?


Under a pair of plastic clips we find a small PCB fitted to the main PCB. In this shot I have actually removed the main PCB already.

What could it be?

IMG_1236 IMG_1235

It is a USI SiP WiFi WM-N-BM-01 radio module with an Atmel ATSAM4S16B microcontroller for interfacing to the thermostat.

Where does it go?


Right to the same 4-pin serial connector we saw last time.

Any other changes from last time?


Thermostat microcontroller is now an AVR XMEGA256 instead of the ATMEGA645V. This upgrades the codespace and horsepower available while staying in the same family.