Picture shows a Pro-Micro clone but I’m now testing with a Sparkfun Pro-Micro and showing same “symptoms”.
I’m building a mechanical Keyboard that uses the QMK firmware and a Pro-Micro. I’ve run into a rather interesting problem that has got me scratching my head. The PCB is this one here http://www.40percent.club/2016/11/mf68-revised-pcb.html. The GERBER files are there if you want to look at the board design. There’s nothing really special about it; standard 68 key configuration. The firmware does all the heavy lifting. Not using any LEDs.
I’ve added a USB mini connector to the board as designed (stronger then Pro-Micro USB connector). The Vcc and GND are wired to the Pro-Micro via the PCB traces. Vcc goes to both vRAW and VCC pins on the Pro-Micro (verified with a meter). Grounds are all connected also.
Now in order to make this work as designed I have to wire a jumper for Vcc, Gnd, Data +, Data - to a USB micro as shown in the picture.
Laptop USB mini > mini on PCB > Jumper to USB Micro > Pro-Micro (Picture)
Here’s the kicker, it doesn’t work. I get erratic operation in Windows. Windows will recognize the keyboard and then after a few minutes I’ll hear the USB disconnect and it’s gone. Sometimes laptop won’t see the “keyboard” at all.
If I connect directly with just a USB Micro to the Pro-Micro everything is fine.
I’ve tried a shielded jumper (grounded at one end). I’ve tried a USB cable with ferrite beads. I’ve tried open wire. The wire is only 2 inches so we’re talking a resonant frequency of ~600 MHz if it’s RFI, it’s way up there and very localized (doubt it).
Based on the schematic of the Pro-Micro I can only surmise maybe there’s some kind of feedback loop in the voltage regulator? I’ve tried with J1 shorted and open. Next step is solder the Pro-Micro back in without vRaw and Vcc and try using just the USB power.
Thoughts? Ideas?
