RPi Interface Rev C

Inspiration

• LTE Breakout

• RPI Interface Rev B

Who

• Daniel Puratich hardware design

• Anthony Luo device selection, firmware

Features we aren’t adding but considered

• no ELRS

  • ELRS changes a lot quickly

  • could be saved for a future revision

• no cameras

  • mounting a camera makes placement complicated

Features

• Begin from RPI Interface Rev B

  • Keep the UART killswitch and one UART passthrough for the RPi to FC direct

  • Keep UART LED indicators

  • Keep CAN circuit

    • this can be used to control the lighting system

• Add an LTE modem to RPi interface rev c

  • relevant discord chat & here

  • quectel module he put

  • Quectel gets USB into the RPi and the STM. RPi eill be used initially and is drawn below because it requires less custom firmwqre, but using the stm long term seems nice.

  • Selected to get maximum mavlink datarate out of the Pixhawk

  • This is not intended to be able to stream data for “groundside compute” for autonomy proccessing as explained in https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2669412363/Autonomy+Compute+Integration+2025?search_id=fe948f35-631d-416c-b4d9-095d8cab5e37.

• Change buck converter to support 48V input so we can connect VBATT

  • this makes architecture decisions and harnessing easier

• Switch STM32

  • STM take in the three uarts form quectel

  • The other STM is smaller and doesnt have enough UARTs for this

  • STM will communicate with the RPi over SPI

• Increase board size a bit

  • this turns the board into a full normal RPi hat

  • This is required for cooling for the LTE module and a simple USB connection for the LTE hat

Part Numbers

• EG915NEAAC-N05-SNNSA

• STM32F415RGT6

Why

• Unlimited range & unlimited datarate is really attractive even if it comes at the cost of some weight and some power consumption.

• Maintaining C2 link is required for flight so full reliance on ELRS is scary even if we have overwhelming evidence for it’s reliability

Block Diagram