The entire control board is based around a Silicon Labs Mighty Gecko wireless module, which is essentially a Arm Cortex processor with a wireless chip stuck on top of it on a PCB with a built in antenna and matching network. I was originally going to use a discrete Gecko series chip and build my own antenna/ matching network, but I decided it would be better keep it simple and use the module to start with. The plan is to drive the motor controllers with the Mighty Gecko and use Bluetooth to send control signals from a computer.
I chose to use single chip motor drivers for both the drive motors, which are DC motors for now, and the weapon motor, which is brushless. The weapon controller is a fan controller, which can supply 1.5A. I think this should be sufficient for a fairly small and light spinning weapon.
I decided to use Eagle for my PCB design because it's free.
Here's the final schematic that I settled on:
And the final board layout:
This ended up being a four layer board with internal ground and power layers. I sent it off for manufacturing at Osh Park and got the three boards I ordered back in just under two weeks. I placed my Digi-Key order when I got a shipping notification from Osh Park and got it on the same day that the boards arrived.
Upon opening the package, I realized that I left the vias exposed and didn't label the connector pinouts. Lessons learned.
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| PCB with quarter for size |
I built out the board in the Invention Studio with a soldering Iron and hot air reflow gun. It was a fairly time consuming process as I had to reflow each of the parts individually, though I think it came out pretty well. I heated the wireless module from the bottom side of the board to avoid incidentally reflowing all of its components and damaging it. Hopefully, there aren't any solder bridges to exposed vias under there. I need to get PTFE jaws for my Stick Vise. The nylon jaws got a bit melted from the reflow gun.
I realized that I used the wrong size connector for the debug header. The 2x5 connector pattern is supposed to be the same size as the connector on the ribbon cable. I'll hack something together for now and use the proper connector on the next version.
Some other thoughts:
- I should have included signal and power LEDs for debugging purposes
- I can probably make the board smaller with the proper size connector
The next step is software and testing, which will likely be an interesting endeavor.
