Earlier today I did the third stream in the Serpano series, this time we focused on the MCU, and as a bonus we managed to squeeze in a quick display and button test.
As you can see, the DC-DC Buck is still bodge city, but the SAMD51 MCU, QSPI Flash and the display are all there, lookin' good!
After soldering those up, I flashed a uf2 bootloader on the SAMD51 using OpenOCD and a CMSIS-DAP dongle and then I made a quick new board define for Serpano in CircuitPython.
That was enough to get the screen going, which I did, by doing a quick draw test, looks good!
We still have a few things to solder + test: the battery charging, the i2c pot used to control the adjustable voltage rails, and the current sensing chip so we can measure the current usage of the adjustable voltage rail.
So during the second stream I soldered and tried to get the DC-DC Buck working, but no luck, I was getting strange voltages and it was all over the place, I'm still not 100% sure what went wrong, I will have to debug it a bit more.
However, after the stream I went ahead and soldered another board with minimum components, just the ones that were required to get the circuit going, then I started measuring and comparing to the reference designs and came to the conclusion that I might've missed some important components, mainly capacitors. I also put in different inductors I had laying around.
As things are right now, I have the second board working with voltage levels close to where they are supposed to be, however I double-checked my math and they should be more on point, so still something seems off, but I think it's good enough to test the rest of the board.
This means that on the next stream we will solder up and try to bring up the samd51 chip with the uf2 bootloader and then CircuitPython.
So the first Serpano stream happened yesterday, with a bit of a rocky start and my multimeter battery dying, we prevailed and got first first part soldered!
The board offers 3 ways to power it, USB PD, LiPo battery, and DC Jack, I soldered the USB connector and the PD chip as well as the DC Jack, fuse and power switch. Then I soldered the first part of the power path, the DC boost, which converts whatever input voltage we have to 15V, and as you can see in the next photo, it works! I tested with 5V in from USB and 12V in from DC Jack and we get a nice 15.1V (as expected).
On the next stream we will solder the 3x DC buck so we can get 3.3V (for powering most of the system), 5V (for battery charging), and the adjustable voltage used on the power rails.