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The Xiaomi Mi Band 8
Like different smartwatch/well being monitoring bands in the marketplace, the Xiaomi Mi Band 8 is filled with 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 attributable to this reality, 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 applications and knowledge onto an Arm microprocessor, however the major methodology for debugging entails the SWD, or serial wire debug, header. Through simply two or three pins, new executables and might 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 check pads, thus permitting Christohpel to solder jumpers and fix them to a programmer. Two UART pin had been additionally out there to behave as serial debugging output.
Constructing a show driver
One of many largest attracts of the watch is its massive 1.62″ AMOLED touchscreen with a decision of 192 x 490 pixels, making it an excellent selection for embedded tasks that require human enter. Nevertheless, figuring out how the show driver was linked to the microcontroller and even what mannequin the driving force is within the first place required some reverse engineering earlier than applications may very well be written.
After analyzing the show, Christohpel found it was pushed by an RM69330, which is widespread 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 check 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 principle attraction, the Mi Band 8 is in the end a health tracker, and due to this fact accommodates sensors for motion/orientation, coronary heart charge measurement, and ambient mild sensing in addition to a Bluetooth Low-Power module. At the moment, Christohpel has gotten the show, touchscreen, and light-weight sensor working in his newest mission launch and shortly plans on finishing accelerometer help.
Going additional
Resulting from 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 comply with extra of Christohpel’s progress as he continues to unlock its performance, you possibly can go to his GitHub repository right here.
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