It’s taken some time, but it’s finally working! It’s hard to debug when you don’t know what’s at fault.
- Is it the PCB design? I’ve never done anything as complicated or as high frequency as this.
- Is the the PCB manufacture? I decided to get the board made by DirtyPCBs rather than home etching, so at least that took one potential source of screw-up out of the equation.
- Is it my soldering? I’ve never done anything as fine as the LQFP (larger chip) and QFN (smaller one on the right). They’re both 0.5mm pitch but at least the LQFP has pins that stick out rather than just metal patches on the edges of a square block.
- Is it the design of the antenna? This is the work of the very talented Mathieu Stephan (from here) so probably not the weakest link.
- Is it the firmware? I’ve had the code running on a MSP430F5529 LaunchPad, but I’ve switched down to a smaller F5510 and reassigned the pins.
Well, it took three tries – as you can see from the scribble on the board above. There’s a mistake around the TPS77333 voltage regulator which truned out to be a footprint error in the Eagle-supplied libraries. It’s now a bodged-in TPS77533. There’s another by the LED which I’ve had to swap for two separate ones rather than a red/green single package. My mistake on the pinout there.
It turns out the problem was the soldering of the QFN packaged TRF7970A. Buying a microscope helped me sort it out and it’s finally there! It’s finally working! There’s more to do, of course. I need to fix the mistakes. The software could be tidier. Version 2.1 will be perfect (probably). I’ll publish the design and code when it’s tidy, but in the mean time if anyone’s interested in any of it, let me know.
I laser cut a simple acrylic enclosure. It’s just black acrylic on the back – with some 5mm neodymium magnets press fitted into holes so it attaches firmly to my PC.
Some clear acrylic makes up the front so I can see the LEDs and the fruits of my labours. M3 nylon bolts go into threaded holes on the rear piece.
It’s been harder and slower than I expected but I’m very happy.