Business in the front, party in the back. Yes, I'm leaving the button like that. It's fine.
This is a Qualcomm Quickcharge Trigger, based loosely on this design, but only rigged for 12V.
Qualcomm's Quick Charge 2.0 sounds like a cool technology: USB power supply can output 9V or 12V, if QC2.0 compatible device requests so. I
When you press the button, it negotiates up from 5V to 12V from any QC 2.0 compatible charger.
Why? The 12V supply that runs my desk is a noisy, cheap pile of garbage that whines at 18kHz all the time, and my hearing is still good enough to hear that all goddamn night. Finding quiet 12V supplies that don't develop inscrutable hums a few months down the line is a crapshoot. On the other hand, cellphone chargers are usually impossibly quiet. I have a loose QC phone charger that I don't need for anything else, so if I can convince it to pump out 12V I can use that to run my desk. Hence, this pile of junk.
Tested and working, all I have to do is press the button to get it to put out 12V. Eventually I might get a 9V zener diode and an LED and set up an indicator that tells me if it's in 12V mode, but for now I'll lean on the fact that I built it and I know how it works.
This is NOT fully wired correctly, as in if you plug the USB cable in upside down it will not trigger correctly. Fixing this is not too hard but would require me to fuck around with the protoboard more than I already have and dealing with protoboard is miserable. I'll just put some alignment markers on the cable I'm using I guess.
I'll have to sit later with a hacksaw and cut this section of protoboard out. Bleh. Building a case for things like this is what makes me wish I had a 3D printer. The exposed pins on the bottom are a short risk so this will get a chunk of cardboard two-way taped to the bottom.
If you ever get a chance to stock up on industry standard barrel jacks, do it, I use these things everywhere.
Quickcharge is a dying protocol, being replaced almost wholly by USB-PD, but USB-PD requires putting an actual microcontroller in the mix whereas this can be done fully analogue, and I believe that even QC 3.0 is still simple enough that a human with some buttons and a few resistor ladders could query basically any voltage it can supply (which is many)
