She’s transmitting! So far so good. Still I made a couple of stupid mistakes:
Stencil: The appertures are far to big for the large parts (Hasn’t Mitch from Hackvana told me this before? Grmbl…). It seems like my solder paste was stored too long at room temperature. The solder and the flux had separated and when I applied it it was flowing everywhere under the stencil. Not good! I mixed the paste with a toothpick and returned it into a clean syringe. Then after several hours cooling in the fridge I tried a second attempt. The PCB and the stencil were cleaned with 91% Isopropanol and the stencil was properly aligned. The cold solderpaste was no longer flowing around and left a clean print on the PCB. Not easy, if you do this the first time…
Serial: The serial connection to the GPS seems to be bedeviled! We’ve had the rxd/txd signals reversed at the PP5 and also on the PP6 PCB. Of course I wanted to fix this, so I immediately changed the Eagle files to have the rxd and txd lines correctly lined up. However I must have forgotten about this, because later I changed them again => Twice reversed = still wrong! How stupid can I be? Well the fix is ugly but easy. I simply need the crossed wire jumpers on the solder jumper pads. I was hoping that this stupid error was finally cleared out, but….
Solar Regulator: I’m not sure yet if it works. Just running first tests. However it seems that the tracker can’t be started with solar power alone. The GPS draws too much current before it gets the first lock. I don’t know what I’ll do about this. Probably the GPS must be switched off at boot and only if the micro recognizes that there is enough power, it should be switched on in a controlled manner. This scenario is predestinated for a brownout, something that I try to prevent under all circumstances. Probably I need to use the hardware solution to switch the GPS off. The transistor is already preconfigured on the PCB, though I currently have only a solder bridge to short it out.
Still plenty things to solve. Noone said this was easy… But still having fun!