Siot splice kit

rPI/Odroid Exansion Board

Features

This board is designed to provide a number of expansion features to Raspberry PI and ODROID-C4 SBCs.

• CAN
• RS485
• 1-wire
• LCD/Touchscreen
• pass through rPI expansion connector to provide use of unused pins.
• XBee socket (Digi, Nimbelink, etc radios)
  • reference design: https://nimbelink.com/products/raspberry-pi-skywire-adapter/
  • supports both standard 40-pin expansion and compute module
• LoraWan radio

MPU Interface

• rPI4 pinout
• ODROID-C4 pinout

MPU/MCU communication link

There is a UART and SPI ports (todo) wired between the host MPU and the MCU on the expansion board.

• UART is likely simplest as the existing CAN firmware implements a USB serial port. Also, for RS485, it is just a pass through.
• SPI would allow us to run both CAN and RS485 at the same time.
• may only be two hardware SPI chip selects, so not sure how well more than 2 SPI devices will work.

MCU Implementation

A STM32F042K4Tx MCU is used to implement the following functionality:

• CAN Interface
• Board ID EEPROM (implements i2c slave)

Reference

• ST Web Site
• Datasheet
• Reference manual
• Programming manual

CAN

Can is typically implemented using a SPI CAN controller (ex MCP2517), but these devices do not offer any buffering so are a poor choice for non real-time operating systems like Linux. Thus, we've chosen to use a MCU to provide the CAN interface and hopefully leverage firmware from the following projects:

• https://github.com/linklayer/cantact-hw
• https://github.com/normaldotcom/candleLight_fw
• SLCAN

HAT ID EEPROM

RS485