I’ve been a fan of the Tado smart thermostat for a while. I didn’t quite make it onto the UK beta test, but bought one as they were first available. Way before Nest, Hive and the others. It’s a nice device. It knows when you’re home and what the weather is, so adjusts your heating to be warm by the time you get home.
Of course, I couldn’t resist a peek inside even before I installed it. It was great to find that the internals involved a TI Stellaris ARM microcontroller in one of the three components, MSP430s on the other two, and all three were linked with CC1101 sub-1GHz radios. The developers were also really helpful. When I had problem with my Sky Broadband’s rubbish DNS, they created and remotely deployed firmware for me within 24 hours. They also told me that it used 6LoWPAN (i.e. IPv6 over a mesh network) to communicate between the components.
Fast forward a couple of years and i decided to upgrade my Tado v1 to a v2. Whilst there was some discount of the list price for returning my v1 device, it seemed far more fun to play around with the hardware. I’m going to hack it. Nothing devious or underhand, of course. I’m just going to make use of this nice piece of hardware.
First the connector. This contains a LM3S9997 microcontroller. This has now been superseded by TI’s Tiva range – and Tado now use a STM32 in the v2 connector. However, there’s nothing wrong with this device. It does the job. A bit of snooping showed a couple of unpopulated SMT headers on the top – and similar large pitch versions on the underside. I traced the ICDI (debugging) pins on the LM3S and discover not only that the go to one of these headers, but that it is even in a standard ARM JTAG header format. Result! Thank you Tado. Hardware developers that care! You’ll see my new 10-pin addition in the photo above, along with the still unpopulated 8-pin header.
All I needed to do was solder on a header and connect an ICDI to it. Unfortunately I couldn’t find the proper debugger – they’re a bit old for what I work with. The newer XDS110 on my CC2650 LaunchPad wouldn’t play with the older LM Flash programmer software. Whilst the really helpful Bluehash over on 43oh.com kindly offered to send me the correct debugger, I decide to see if I could hack something together. A bit of ribbon cable and some iffy soldering and my old Stellaris LaunchPad was called into action. Now I could dump the flash contents – so that I can revert to if needed – and program new firmware.
All I’ve done so far is dump the Tado firmware and take a peek. Nothing too revealing in all those bytes – other than a reference to Contiki 2.6. Whilst I don’t know much about Contiki yet, I know it’s TI’s preferred route to getting 6LoWPAN working to provide an edge router for newer devices like the CC1310 – an ARM microcontroller with a Sub-1GHz radio built in. Anyway, that’s enough for now. We have a vague plan…