Split-Flap Display

A modular, 3D-printed split-flap display controllable over RS485 from a Raspberry Pi. Each module holds 64 characters and modules can be chained together to build a display of any width.

YouTube Build Video: https://www.youtube.com/watch?v=-C8_AtxEEQc

---

How It Works

Each module contains:

• A 3D-printed drum that holds 64 individual flaps (one per character)
• A stepper motor driving the drum through a gear train
• A Hall effect sensor for homing
• A custom driver PCB (ATtiny1616 + RS485 transceiver + ULN2003 stepper driver)

Modules communicate over a shared RS485 bus. A Raspberry Pi running a Python web interface sends commands over USB-RS485 to each module individually by address.

---

Repository Structure

cad/                       - 3D printable parts (Bambu Lab profiles included)
flaps-generator/           - OpenSCAD code to automatically generate (custom) flaps
pcb/
  driver-v2/               - Driver PCB KiCad project used in the video build
  driver-v3/               - Updated driver PCB KiCad project, slightly cheaper to manufacture
  bus-board/               - Bus board KiCad project
  bus-board-5-module/      - 5-module variant of the bus board
firmware/                  - Arduino firmware for the PCBs
frontend/                  - Raspberry Pi Python web frontend
docs/datasheets/           - Component datasheets
BOM.md                     - Bill of materials

OnShape Model: https://cad.onshape.com/documents/87c916b33ca5d6492b457485/w/b3e5f0f05f6619e6e7931347/e/582ef2164e20b0aa994708ab

---

Parts List

See BOM.md for the complete bill of materials, broken into three sections:

• PCB / Electronics — all SMD components with JLCPCB part numbers for easy ordering
• Module BOM — 3D printed parts and hardware per module, with quantities scaled to 45 modules
• Other Components — system-level parts (Raspberry Pi, power supply, C14 connector, etc.)

---

Ordering the PCB from JLCPCB

The driver board is designed to be ordered from JLCPCB with their PCB Assembly (PCBA) service so the SMD components arrive pre-soldered.

Step 1 — Export Gerbers from KiCad

1. Open the project in pcb/driver-v2/
2. In KiCad PCB editor, go to File → Fabrication Outputs → Gerbers
3. Export to a folder, then zip the contents
4. Also export the drill file from the same menu

Alternatively, pre-exported Gerber and PCBA files are already be present in the KiCad project folder.

Step 2 — Upload to JLCPCB

1. Go to jlcpcb.com and click Order Now
2. Upload the Gerber zip file
3. Set your desired quantity (minimum 5)
4. Leave most settings at default; adjust PCB colour if desired

Step 3 — Enable PCB Assembly (PCBA)

1. Toggle PCB Assembly on
2. Select Standard PCBA and set the assembly side to Top Side
3. Click Confirm

Step 4 — Upload BOM and CPL Files

1. Upload the BOM file from the KiCad project folder — this maps component values to JLCPCB part numbers. The part numbers in BOM.md match what is in this file.
2. Upload the CPL (Component Placement List) file — this tells JLCPCB where each component sits on the board
3. Review the component matches on the next screen. All parts should auto-match using the C-numbers in BOM.md. Confirm any that need manual review.

Step 5 — Review and Order

1. Check the parts list — confirm quantities and part numbers match the BOM.md PCB section
2. Proceed through the review screens and place your order

Note: A few through-hole parts (pin headers, JST connectors) are not included in PCBA. These are listed in the BOM and will need to be soldered by hand.

---

3D Printing

All printable files are in the cad/ folder. A Bambu Lab print profile is included in cad/64FlapsWithLetters (parts and bambu print profile)/ for the flaps. Print the flaps in the correct colour for each character — see the video for details on the full 64-character set.

Parts per module:

• Enclosure Body, Right Cover, Left Cover
• Drum Body, Drum Cap
• Motor Gear, Center Gear, Gear Plate
• DIN Rail Mount, Wire Retainer
• 64 Flaps

Creating your own flaps

If you want to generate your own flaps, with your own font, size and characters, you can use the OpenSCAD script to automatically generate this.

---

Firmware

Located in firmware/. The firmware is Arduino-based and targets the ATtiny1616.

• Flash via UPDI programmer (see https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md if you need to make one)
• Each module needs a unique address (0–44) stored in EEPROM. Be sure to edit this between flashes.

---

Frontend

Located in frontend/. A Python web interface running on a Raspberry Pi sends display commands over USB-RS485 at 115200 baud.

Need a USB-serial dongle. I used this one: https://www.adafruit.com/product/5994

---

License

This project is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0).

You are free to share and adapt this project for non-commercial purposes, as long as you give appropriate credit to Adam G Makes and distribute any derivatives under the same license.