Short Summary

I've been building and developing autonomous planes, multicopter and rovers for over 5 years. Much of this has been through the CanberraUAV and Ardupilot organisations.

As these autonomous vehicles increase in their complexity, it's becoming more and more common to install a small Raspberry Pi to handle image processing, high level commands and communications.

Up until now, however, there has not been an easy way to connect the Raspberry Pi to the other systems in the vehicle - power, flight controller, sensors and other devices. The current method of custom wire harnesses and soldering can easily lead to power or communication failures.

The Pi-Connect is designed to make this integration easy and reliable by using a HAT on the Raspberry Pi that provides power, telemetry, UART and ADC interfaces. All you have to do is connect it to your flight controller and power systems and you're up and running!

 

What We Need & What You Get

At this point I have a working prototype of the Pi-Connect board. Several of these have gone out for beta testing with users around the world. Based on their feedback and my own testing I'm now able to manufacture the boards at a larger scale.

The below image shows the evolution of 4 revisions of the board. The 3rd image is the board used in beta testing and the rendered image is the proposed final version of the board.

Evolution of the board, left to right.

In order to manufacture the boards at a reasonable cost, I need a minimum number of orders. Scale does matter in the manufacturing industry!

The funding I raise here will be used for:

1. Finalising the board design and manufacturing a small run for testing
2. CE and FCC certifications
3. Manufacturing the boards

The finalisation of the board design (ie the differences from the beta board to the final board) will include an uprated power supply (from 3 to 3.5A), a push button instead of switch for the power, addition of a power plug and a rearrangement of the UART port types and placement. See the below image for an indicative layout.

The boards feature:

• 5.1V, 3.5A power supply that can supply the full 2.5/3A power to a Raspberry Pi without any voltage sag. The other 0.5A is used for the powered UARTs. It can accept anywhere from 7 to 30V input.
• Power plug (Molex Nanofit 1053131102)
• On/off toggle button with header for fitting a custom button.
• 3x UARTs. One is in Dronecode-standard JST-GH format, the two others (powered) in 0.1" FTDI header standard (one at 3.3V, the other at 5V). The two powered UARTs (SC16IS752)can collectively use up to 0.5A.
• 3.3V ADC (MCP3008) with inbuilt voltage monitoring.
• Compliant to the Raspberry Pi uHAT standard. This includes an EEPROM for HAT capabilities, backpower protection and 4x screw holes that match with the Raspberry Pi Zero (2x will match the regular Raspberry Pis) for secure mounting.

 

Major features and indicative layout of the final board

In terms of reliability and protection, the board will have:

• On shutdown, the power button will issue a shutdown command to the Raspberry Pi and will for it to cleanly shutdown before cutting power.
• Reverse voltage and ESD protection on the power input.
• Overcurrent protection on the powered UARTs and ADC. A short circuit on either will not affect the power to the Raspberry Pi.
• Auto thermal shutdown on the power supply.
• All parts used are high quality "name brand" parts, including TI, Yageo, Vishay and ON Semiconductor.

 

Pi-Connect in action - feeding in data from a Pixhawk, Arduino and analog light sensor

The board does not require custom software to access its features. Rather, it takes advantage of existing Raspberry Pi system drivers. All that is required is a few extra lines to the /boot/config.txt file.

For those that want a more complete solution, a small web application (run from the Raspberry Pi) can be used to manage and view the UARTs, ADC and network configuration.

Optional Web-based GUI for managing the UARTs and ADC

Each board will come with a 15 cm power cable and 15 cm telemetry cable, each with the appropriate plugs for the Pi-Connect.

The Impact

The Pi-Connect will make it easier to connect your Raspberry Pi to the rest of your on-board systems in your autonomous air/ground/water vehicle.

Specifically, it will allow:

• Usage of multiple high-power USB devices (such as 4G dongles and cameras) - without having to worry about power supply sag or reliability
• Monitoring of on-board system voltages and temperatures via the ADC
• Interfacing with serial devices (such as Arduinos, gimbals or smart cameras) via the additional powered UARTs

 

The Pi-Connect is ideal for autonomous vehicle developers or system integrators who want to reduce the size, weight, complexity and costs of cabling up a Raspberry Pi into their vehicles.

Risks & Challenges

The development of this board has already gone through 3 versions over that past 9 months. All functionality has been tested and confirmed in the latest board revision.

The UART, power button and ADC are all devices with existing drivers within the Raspbian OS. Thus, no driver development will be required.

The budget for the project includes test equipment, certification costs, cables, packaging and manufacturing. There is a small contingency for exchange rate fluctuations and a second test batch of boards (if required).

Project Budget

In terms of risks, there is:

• Bug in the final board revision or failed FCC/CE certification. This may delay the shipping time of the boards by 1-2 months while I fix the issue(s). This is unlikely as there's only minimal changes from the current prototype board to the final (mostly layout changes).
• Board manufacturer quality not suitable. The manufacturer used for these boards (Seeedstudio) I have used for all 3 prototypes of the board (including their full PCB assembly service in the current board revision). In this time I've not had any board failures due to manufacturing issues.