For the first RPi power-up in PiCon One, I prepared the Raspberry Pi SD card, using the original Raspbian Lite image. After flashing the card, I updated /boot/config.txt to enable the serial console, adding 'enable_uart=1' at the end of the file. The boards 6-pin console connector links up to GPIO14 (pin-8 TXD) and GPIO-15 (pin-10 RXD) on the RPi, and is made to fit common USB console cables such as FTDI RS232R cable with the 6-pin plug.
The first power-up of a new "alpha" board is a big moment: Will it work at all? And what will it be that I missed this time?
For the good news, the board lights up and the serial console came to life. For not so good news, the board went into a permanent reboot cycle. This happened six seconds into the boot process, exactly when it enables peripherals and I2C. I got a power surge issue.
Good power rail design is one of my weak spots, and I have been taking shortcuts for the "alpha" board. I only roughly estimated the power draw, didn't account for peaks, and I am running dual power 5V/3.3V by using 3.3V supplied from the RPi.
A quick fix was to solder a sufficiently strong stabilizing capacitor. I added 470uF to the 5V power rail on the back of the board. Now the boot process completes fine, and the board is running nice and stable. The 24-test with basic load went OK, I also needed to check out the heat situation inside the enclosure. Doing another proper "burn-in" test is on my "To-Do" list.
If you are reading along and are experienced with power rail design: I'd love to hear recommendations for the next board revision. Improving the power rail is high on my list to get right.
With the board now operating stable, its time to verify and set up the peripherals.