Adafruit 16x24 red LED matrix (HT1632)

Troubleshooting
2
  1. Is your code being flashed (D7 indicating, or other way to tell)? See How to get started?
  2. Could it be 3.3V out of Photon, is a bit shy for a 5V input?
  3. What does " I can’t seem to get the display to work" mean? Wrong characters, no lights, ?