Introduction

• What

  • UART and GPIO 1:1 adapter for https://holybro.com/collections/standard-gps-module/products/m9n-gps GPS to CAN.

  • Support full pixhawk standards and our common CAN circuit

  • Basically just copy ESC CAN Adapter schematic but replace the DSHOT connection with a UART connector for the GPS. Layout wise you can make it a bit bigger, but keep all components on the same side so it’s easier to solder.

• Why

  • this is far cheaper than GPS devices that support CAN

  • allows us to space out the GPS antennas pretty far from each other

    • an example system is drawn in ESC CAN Adapter for why CAN is an advantage

• Competition

  • products that do this integrated already

  • https://holybro.com/collections/h-rtk-gps/products/dronecan-h-rtk-f9p-nxp-32k1-helical

  • https://holybro.com/collections/h-rtk-gps/products/dronecan-h-rtk-f9p-rover

  • https://holybro.com/collections/h-rtk-gps/products/h-rtk-unicore-um982

• Who

  • EE Reviewer: @Nolan Haines @Nathan Green @Ryan Scomazzon

  • Architecture & High Level Project Requirements: @Daniel Puratich

  • Engineer: @Omar El-Sawy

• When

  • unknown.

• Where

  • add links to stuff here please …..

• Table of contents:

Design

Open

Members:

• @Omar El-Sawy

Design Overview

The GPS CAN Adapter is as named, an adapter built for the GPS Sensor (MD9 https://holybro.com/collections/standard-gps-module/products/m9n-gps or MD10 https://holybro.com/collections/standard-gps-module/products/m10-gps ), 1 Primary, 1 Second. It involves converting UART to CAN with JST on both Ends, and vice versa using an STM32 chip in the middle as the translator. The UART sends/receives information at a rate of 115200 bits/s, which is processing by an STM32 chip, and then finally converted to CAN FD which transfers at a rough frequency of 15MBits/s.

Goal:

Create <$20 boards adapter to avoid buying more expensive GPS Sensors with CAN Support.

Why this project?

• We want to space GPS antennas out for better reception so we want to add CAN support to facilitate this. Also, better busability.

• Some GPS antennas support CAN but more expensive, doing this should be cheaper

Why CAN?

• CAN works better in noisier environments

• Higher Speed Communication

• Less noise and more signal integrity over long distances

Deadline:

• Ideally designed by the end of S24, bringup F24.

Block Diagram

Component Choice

1. STM32 Unit

Requirements:

• UART: 115,200 bits per second => 14,400 bytes per second,

• CAN: 1,000,000 bits per second => 125,000 bytes per second

• UART to CAN Performance:

  • Each byte is a UART interrupt, Interrupt Service Routine roughly takes 50 CPU Cycles

  • Each byte, Parsed/Converted might take 100 CPU Cycles

  • Each Byte Sent here might take 50 CPU Cycles

  • Total: Roughly 200 CPU Cycles

• UART to CAN Performance:

  • Each byte is a CAN interrupt, Interrupt Service Routine roughly takes 50 CPU Cycles

  • Each byte, Parsed/Converted might take 100 CPU Cycles

  • Each Byte Sent here might take 50 CPU Cycles

  • Total: Roughly 200 CPU Cycles

• STM32 Performance Requirement:

  • Total CPU cycles per second = 400 cycles/byte * 14,400 bytes (5.76 million cycles/second)

  • 5.76 MHz is the requirement but for safety lets multiply it by a 4x factor

  • 23.04 MHz Performance Requirement

• STM32 Port Requirement:

  • 1 CAN 2.0 Port Group

  • 1 UART TX and RX Pin

• STM32 Power Requirement:

  • As little power draw as possible

2. UART JST Connector

Best Choice: GHR-10V-S (https://www.digikey.ca/en/products/detail/jst-sales-america-inc/GHR-10V-S/807822?s=N4IgTCBcDaIOIAkBKBaAjABgGooMogF0BfIA )

Requirements:

• 10 Female Pin Slots

  • Has to work with the (M9N or M10N) GPS UART Connection and the primary one comes with 10 pins (https://holybro.com/products/m10-gps?srsltid=AfmBOopdTetTEMH0Xjdp2ZFBCizDOoz29fGs5ZMFO5TMhK5-Mm1J1kId ) (https://holybro.com/products/m9n-gps?srsltid=AfmBOorPXKD21Sc--PaH2gInPK4FlUbQ3PzcRkFwGLW4Bmo67MPXtt9r )

Pros:

• According to specs and recommendations of GPS connector GHS 1.25mm 10 pin male on their gps sensor

3. Programming/Flashing JST Connector

Best Choice: BM06B-GHS-TBT (https://www.digikey.ca/en/products/detail/jst-sales-america-inc/BM06B-GHS-TBT/807804 )

Requirements:

• Ports (in order):

  • 3V3

  • NRST

  • SWO

  • SWDIO

  • SWCLK

  • 3 GNDS

Pros:

• Default for flashing as said here: (STM32 Programming Connector Standard )

4. CAN Transceiver

Best Choice: TJA1051TK/3,118 (https://jlcpcb.com/partdetail/NxpSemicon-TJA1051TK_3118/C124020 )

Pros:

• recommended by pixhawk spec and used in our common CAN circuit.

Cons:

• Expensive

5. CAN Bus Connector

Best Choice:

Pros:

• Standard used by the team

4. Power Input

Best Choice: XT90

Pros:

• Standard used by the team for power supply

Considerations with CAN/UART:

CAN:

UART:

Mounting Board

Resources:

• System Architecture: https://uwarg-docs.atlassian.net/wiki/spaces/ARCHS22/pages/2249981953