The Xiaomi Mi Band 8
Like different smartwatch/well being monitoring bands in the marketplace, the Xiaomi Mi Band 8 is full of sensors, communication capabilities, and an environment friendly battery administration system- all in a compact wearable. The band runs on an Arm Cortex-M4 microcontroller inside an Apollo4 Blue Lite SoC from Ambiq, and resulting from this truth, Aaron Christohpel (atc1441 on GitHub) realized that he may hack it to run customized firmware due to the Ambiq SDK.
Accessing the MCU
There are a few methods to load packages and knowledge onto an Arm microprocessor, however the major methodology for debugging entails the SWD, or serial wire debug, header. By way of simply two or three pins, new executables and will be despatched and subsequently monitored with a debugger. Conveniently, the Reset, SWD Clock, and SWD IO had been all uncovered on the underside of the PCB as take a look at pads, thus permitting Christohpel to solder jumpers and connect them to a programmer. Two UART pin had been additionally obtainable to behave as serial debugging output.
Constructing a show driver
One of many greatest attracts of the watch is its giant 1.62″ AMOLED touchscreen with a decision of 192 x 490 pixels, making it a fantastic selection for embedded tasks that require human enter. Nevertheless, figuring out how the show driver was related to the microcontroller and even what mannequin the driving force is within the first place required some reverse engineering earlier than packages may very well be written.
After analyzing the show, Christohpel found it was pushed by an RM69330, which is frequent for spherical LCDs, together with the pins being utilized by the microcontroller’s SPI bus. Armed with this information, he constructed a driver that might write pixel knowledge to the display screen’s inside buffer after which present it. The ultimate take a look at of this proof of idea concerned exporting a number of frames from Rick Astley’s notorious “By no means Gonna Give You Up” video and looping by means of them to create a easy animation.
Different peripherals
Though the display screen is the primary attraction, the Mi Band 8 is finally a health tracker, and subsequently incorporates sensors for motion/orientation, coronary heart price measurement, and ambient mild sensing in addition to a Bluetooth Low-Power module. Presently, Christohpel has gotten the show, touchscreen, and light-weight sensor working in his newest undertaking launch and shortly plans on finishing accelerometer help.
Going additional
On account of its low price and spectacular array of sensors and display screen, the Mi Band 8 seems to be a promising system for future hacking and adapting into different tasks. To observe extra of Christohpel’s progress as he continues to unlock its performance, you may go to his GitHub repository right here.