It's a nice keyboard but it surely does not examine to the complete machined aluminium frame on the MNT keyboard. That is another very fastidiously designed aluminium half In the close-up above you may see the opening for the USB-C connection for the keyboard and the internal cutouts for the show daughterboard with the screw mounting. The design for the audio at FOSDEM would be less complicated though, no networking is required on the mixer but as a substitute the USB connection could be used for control. The ribbon connector is the connection to the OLED show board. In the current revision of the board this has been replaced with the TPS65130 regulator. It's a switching regulator that runs at 100Khz max. Specifically I had a capacitor in the feedback path for the switching regulator that was two orders of magnitude too giant. This receives 5V from the USB connector or the battery energy (or both) and feeds them into the regulator to generate the 3.3v rail. With just a few extra parts the resistor divider can be fully disconnected from the battery stopping the facility leakage.

This revision of the facility supply was scrapped because with the right inductor the facility provide merely grew to become too large for the board and i did not wish to make the board any bigger because the inside of the FOSDEM box could be very area constrained. This version of the facility supply was not full but since it was missing a couple of capacitors and i came upon that the inductor I chosen was manner too small to function correctly. It seems these capacitors were non-compulsory anyway in accordance with the datasheet so after removing these from the facility supply it already grew to become a lot more reliable. Or implement a phantom energy provide. After coping with all this I now finally understand why so much of the audio gear has old-school transformers to power them: it makes it very simple to make a twin-rail supply. The MCP34063 is also a long time old expertise by now. Then I remembered I have an old Behringer Ultramatch Pro within the dusty racks of decommissioned hardware. I have not been capable of finding just an inventory of CEC opcodes and their arguments so I am unable to actually confirm this.

Thanks to the schematics being out there in the guide it is simple to search out that that is the swap to allow programming. This being a extra niche product sadly does make it a bit on the costly side. After initially working for a bit I did not get it to generate the correct voltages once more, even after restarting the board. I had additionally added an OLED panel to the board for testing so I added a little bit of code that shows the audio ranges of all the inputs and outputs of the board on that screen. The components of the hardware design are modular sufficient to reconfigure them for other audio wants and now the line-stage inputs are working it will likely be neat to figure out a digitally managed microphone preamp. This additionally means it's now attainable to construct the firmware for the FOSDEM audio mixer with out first downloading a pre-compiled ARM compiler so it will probably run shortly in Alpine in CI.

At the very least the board was now dependable enough that I could work a bit on the firmware and all of the functionality that did not rely on the opamps was working nice. While loads of the hardware is specified for the precise requirements of a FOSDEM room it does provide a neat base to work off for designing digital audio mixers. To start I decided to open up one of many USB powered audio interfaces I already had and see what the designers of that system did to repair this. To repair that I changed the best management button into the Hyper key, that is the button with the three dots on it. The management of the mixer would happen by means of the infrastructure FOSDEM already has where the volunteers in the rooms can control the containers with a webpage from a phone and a few software on the SBC contained in the field will communicate with the mixer over a serial port. There's additionally an preliminary implementation of the serial management protocol.