The first version may be a bit of a stretch — I tried to make it as small as possible, fitting in the 5x5cm limit of PCB manufacturers, so that it will be cheap to make the PCBs. Using the cheap ST7735 TFT display, and a cheap ATSAMD21E chip. I also tried to put all the components on one side of the board, but failed with that — the power and reset switch had to go on the back, as well as the buzzer.
There is a number of options you have for display shields for the D1 Mini: there is the nice OLED shield, there is a shield with a single WS1228B neopixel, there is the #D1 Mini Matrix Shield I’m still working on. But there is no high-resolution color display you could just slap on it. This “shield” doesn’t really deserve the name, it’s just a simple breakout board that connects the ST7735 display module with the SPI pins of the D1 Mini, and adds a trim pot for brightness control.
To save some pins, the CS pin is hardwired to GND, and the A0 pin is connected to MISO. That means you can’t connect other SPI devices while this is in, but that’s a rare enough case for me to care. It uses four GPIOs total, from GPIO12 to GPIO15. The backlight is connected to the 5V supply (to not strain the on-board 3V3 regulator) through a trim pot, so you can adjust brightness.
I used alternating holes for the module’s header, so that with some luck you should be able to plug in the module directly, without soldering a female pin header there — that should also save some space.
1Bitsy 1UP is a retro inspired handheld game console, the design is based on the 1Bitsy STM32F415RGT6 ARM Cortex-M4F 168MHz 192kb RAM and 1MB Flash micro controller. 2.8″ TFT with capacitive touch, SDCard Reader and a few other components.
The display used is a TFT LCD with I2C CapTouch and ILI9341 driver. (should be compatible with the display sold by Adafruit on their breakouts as well as the buydisplay.com 2.8″ tft with CapTouch sensor)
[Max K] has been testing the battery life of his self-designed watch under real-world conditions. Six months later, the nominally 3 V, 160 mAh CR2025 cell is reading 2.85 V, so the end is near, but that’s quite a feat for a home-engineered smart watch