- HUD esp32-c3 xaio with waveshare oled display SSD1309 128x64 connected via SPI https://www.waveshare.com/wiki/1.51inch_Transparent_OLED the pins are 

#define OLED_CLK  7   // D5 - SPI Clock (SCL/SCK)
#define OLED_MOSI 6   // D4 - SPI Data (SDA/MOSI)
#define OLED_RES  3   // D1 - Reset
#define OLED_DC   4   // D2 - Data/Command
#define OLED_CS   5    // D3 - Chip Select

This device receive EUC battery voltage and current speed from the HUB. It also has 3 buttons left, middle and right respectively attached to pin d06, d07 and d08