Wow. Today I soldered the final pieces onto the board, and ran into huge problems. There is good news and bad news:
- The ISP talks to the AVR correctly, and I burned the bootloader onto the chip.
- Some of the LEDs light up
- The voltage regulator puts out 5V
- Plugged the board into a mislabelled power supply, and let the magic smoke out of the voltage regulator (oh no!)
- Got bizarre LED output from a seemingly-simple serial out command (see the video)
- The FTDI doesn’t work
- I have no idea where to start looking
The code seems okay, and the schematic looks correct. However, the oscilloscope shows a hideous CLK (register clock) signal that modulates all around and can’t stay steady. The result suggests an inadvertent RC circuit with painful oscillations.