Hey Geekhack,
I recently built my first keyboard using a Rev2 Zeal60 RGB LED PCB I got from the recent MassDrop offering. Everything went well and the process from start to finish has gotten me pretty hooked on this hobby.
I started running into some issues when I attempted to add underglow via an led strip. I eventually got it working but made the mistake of changing two different things between two troubleshooting attempts, so now I have questions. Below is the guide I originally referenced as well as the components I used.
I should note at this point, I did all my firmware through QMK's master branch using the Zeal60 keyboard folder from Wilba6582's fork. I wanted to learn QMK as part of this, but still wanted to at least stay in the spirit of using the software Zeal recommended.
Tusing's original wiring setup suggested connecting the strip's 5v pad to the F1 thermistor. Baethus' plank underglow guide,
which is referenced in the QMK documentation, recommends going off the VCC pinout.
Considering Tusing recommends increasing the maximum power consumption to 900, is their approach trying to access a more stable power source for that level of power or will the VCC pinout still be able to service the LED strip without issue?
That question is part of why I connected to the VCC pinout instead of the thermistor. When I followed Tusing's guide to the letter, I found that QMK threw a wraparound errror when I tried to make the hex file. Digging into the source code, it looks like this is due to the consumer of USB_MAX_POWER_CONSUMPTION, MaxPowerConsumption, being a uint_8 variable. I mainly work with OO languages, but if I remember right that's basically an unsigned char which should only have values between 0-255. I haven't debugged deep enough to see if there's any magic happening to defeat that limitation. If this were purely software, I'd have no qualms changing from an 8 to 16 bit value to see what happens. Considering there's hardware I've put time, care, and money into connected to this, I'm very hesitant to make this change without being better informed. All things considered, I haven't even really added the two other strips I intend to use on the current configuration to see if a deeper dive is even needed or if the brightness is fine as is. Can anyone more experienced than myself weigh in?
My intention is to do an updated write up that details, start to finish, everything involved in this mod. I want to spell out everything so anyone new to the hobby, like myself, can not only have a guide to follow but also be presented with factors to consider before taking on a mod like this.
edit - Still haven't found any answers yet. I've posted to the google group for the LUFA usb drivers to get more info around the safety of changing the variable. Beyond that, I'm also rewiring my LEDs tonight to see if there's a noticeable change in brightness by using the F1 thermistor over the VCC pinout.