As regular readers of my blog will know I’m an ardent fan of the Nordic nRF51 (and nRF52) series of Bluetooth Low Energy MCU’s.
So when I found out that a number of fitness tracker / smart watches, used the nRF51822 and could be easily opened and reprogrammed I was very interested and ordered 2 of them to try.
Unfortunately soon after I ordered them, it became clear that the model I had ordered would probably not be powered by an nRF51822, and hence started my quest to understand what models of smart watch do, really, use the nRF51.
Firstly, the model number of the watch I ordered was a TW64 – which is where the confusion starts.
A number of completely different watches are sold as a TW64 but contain completely different processors.
The ones I ordered, from eBay, had the Quintic QN9021 ( http://www.nxp.com/products/microcontrollers-and-processors/more-processors/application-specific-mcus-mpus/bluetooth-low-energy-ble/ultra-low-power-bluetooth-le-system-on-chip-solution:QN9021) listed as the main processor, however when I opened mine up, it actually contains a Dialog DA 14850 processor (http://www.dialog-semiconductor.com/products/connectivity/bluetooth-low-energy/smartbond-da14680)
Either way my watch unfortunately didn’t contain an nRF51
However searching for “TW64 nRF51822” does find some watches marketed as a TW64 which do contain the nRF51822, which lead me to Shenzhen DO Intelligent Technology Co., Ltd. on Alibaba.
I contacted them to find out more details and found that all of their smart watch/ fitness trackers use the nRF51822
Their product numbers are P101,P102,ID100HR,ID105,ID105HR,ID107,ID107HR,ID101HR,ID110HR,ID111HR and ID115HR
So if you are looking for an nRF51 based smart watch, your best bet is to search using one of those model numbers, and double check the details in the eBay / AliExpress / Gearbest etc listing to confirm it does mention the nRF51822
In the end I decided to buy an ID100HR and a ID107HR, via AliExpres.
When my ID100HR arrived, and I unscrewed the back of the case on the watch, I was pleasantly surprised to find that the watch contained an nRF51822QFAC, which is the 32k RAM version (top of the range for this MCU), and also that the watch has both the 16Mhz main crystal and also the 32kHz low power mode crystal.
With the help of Goran Mahovlic, I can now reprogram this watch using the Arduino IDE and can read from the accelerometer sensor, and write to the display, as well as get input from the button and turn on and off the vibration motor.
I have yet to investigate how the Silicon labs Si1142, Heart Rate sensor is interfaced to the MCU, but as its I2C, its possible its wired onto the same bus as the Kionix kx022-1020 accelerometer.
So it should be possible to use this feature of the watch as well.
If anyone wants to give this a try for themselves, please also read my previous postings about programming the nRF51822 using the Arduino IDE and also refer to my latest Arduino for nRF51822 repo on github.