Jan 14, 2018 update: I have replaced the board layout picture with a new version that reflects significant repositioning of the components which leads to simplification of the traces and better access to usb ports and microsd cards in the final design.
There is something relaxing about nudging traces and components around on a pcb layout. Last night I spent some more time working on a new board design which I present here:
If you can’t guess from the schematic, this is a fixed wing autopilot built from common inexpensive components. The whole board will cost about $100 to assemble. I figure $20 for the teensy, $20 for the pocketbeagle (on sale?), $15 for a nice voltage regulator, $15 for the IMU breakout, $25 for the board itself. Add a few $$$ for connectors, cables, and other odds and ends and that puts the project right around $100.
The layout is starting to come together. It still requires some more tweaking. I’d like to label the connectors better, thicken the traces that carry main power, and I’m sure I’ll find some things to shift around and traces to reroute before I try to build up a board.
I am doing the design work in ExpressPCB, mainly because I know how to use this tool, and in the small quantities I would need, board prices are not a big factor. The board itself will cost about $25/ea when ordering 3 (that includes shipping.)
This is actually an evolution of an autopilot design that has been kicking around now for more than 10 years. The basic components have been improved over the years, but the overall architecture has remained stable. The teensy firmware and beaglebone (linux) autopilot software are complete and flying — as much as any software is ever complete. This board design will advance the hardware aspects of the AuraUAS project and make it possible to build up new systems.
This new board will have a similar footprint to a full size beaglebone, but will have everything self contained in a single board. Previously the system included a full size beaglebone, a cape, plus an APM2 as a 3rd layer. All this now collapses into a single board and drops at least two external cables.
A few additional parts are needed to complete the system: a ublox 8 gps, a pair of radio modems, and an attopilot volt/amp sensor. The entire avionics package should cost between $200-250 depending on component and supplier choices.
Source code for the teensy firmware, source code for the beaglebone AP, and hardware design files are all available at the AuraUAS github page: https://github.com/AuraUAS