rpi-rgb-led-matrix/adapter/active-3

Adapter PCB to support up to 3 panel chains

• Supports up to three panel chains for newer plus models and Raspberry Pi 2 that have 40 GPIO pins.
• Uses HCT245 to level shift signals from 3.3V to 5V and shield the Raspberry Pi GPIOs from overloading.
• Open source KiCAD PCB EDA format.
• Optional: Pads to power the Pi with 5V, including optional capacitor footprints (use something like 22uF-100uF; might be useful to smooth noisy power supply in particular if you operate the panels from the same supply. I use a 22uF/6.3V ceramic capacitor).
• Connector for RxD input (literally the only GPIO pin left) in case you want to make your panel controlled with a serial interface (3.3V logic level).
• (not very pretty layout, was just lazy and let the auto-router generate the first pass)
• BOM:
  • 4x 74HCT245 or 74AHCT245 in 20-SOIC, 7.5mm package which should make it easy to hand-solder.
  • 4x 100nF ceramic capacitor (0805 package)
  • 1x 10kOhm resistor (0805 package)
  • 3x 16pin IDC (=2x8) male receptible to connect the panels.
  • 1x 40pin female connector to connect to the RPi.
  • 1x (optional) 22uF .. 100uF capacitor for 5V rail.
• The Gerber FAB files are provided as active3-rpi-hub75-adapter-fab.zip

The board is also shared on OSH Park (not affiliated).

Essentially, this is connecting the output pins through level shifting buffers (they are operated at 5V, but the HCT series chips accept 3.3V input levels from the Pi). The strobe, OE and clock signals are separately buffered for each connector.