Splitflap

Split Flap clock or calendar utilising four 28BYJ-48 stepper motors.

Bill of materials

What is needed for one digit.

Pinout

Motors:

Other GPIOs

Assembly

One assembled PCB which functions as the main board can drive four split flap digits including itself as well as three additional passive digits. Looking from the front of the clock / calendar the unit with the populated PCB is to the very left with the barrel jack protruding outward to the left side.

• On the three unpopulated PCBs the Hall sensors circuitry above the spool axis has to be provided. For this R7 can be shortened using a solder bridge, the Hall sensor (AH1815-W7) as well as the R1 resistor (10k 0603) need to be mounted. C1 (100nF 0603) can be omitted:

• Using M3x5 screws mount all four motors directly to the corresponding PCB using the spacer where it says "28BYJ-48". The nuts go to the other side of the PCB where the spacer has two cutouts for both nuts.

• On the main board connect the motor to the "Motor A" connector. The cable can be looped and secured using a zip tie threaded through the two holes next to the motor.

• On the main board solder the three switches and the RGB LED to the backside of the PCB.

• Solder the DCF77 connector to the pcb and temporarily tape the ferrite antenna to the PCB to protect the thin copper wires from the coil around the antenna.

• Add cog wheels with the M3x8 screws on two different sides

• Add the spacer

• Add the cover

• Connect all hall sensors

• Prepare the spool

• Add standoffs female-female or standoffs male-female respectively

• The driving cog wheel is assembled as follows:

    M3x16 + 5 washers + m3-nut-cog + 3 washers

The PCB

PCBWay kindly offered to sponsor the manufacturing and assembly of the second iteration of this pcb.

In this project the PCBs are used in both the electrical as well as the mechanical realm. The motors and cog wheels are directly mounted onto the pcb and for one clock or calendar four pcbs are stacked together.

The PCBs turned out flawlessly and the ordering process was smooth and efficient.

PCB V2.0

PCB V1.0

Flashing the PCB

cd ~/Downloads
IMAGE=ESP32_GENERIC_S3-FLASH_4M-20250415-v1.25.0.bin
wget https://micropython.org/resources/firmware/$IMAGE -nc
PORT=/dev/cu.usbmodem14401
esptool.py --port $PORT erase_flash
esptool.py --port $PORT --baud 460800 write_flash --flash_size=detect 0 $IMAGE --flash_mode=dout

Credits / Thanks

Troubleshooting

Special thanks to greybeard and KubaO who helped to trouble shoot some serious issues that arose during the development of the PCB.

3D models

• Credits for the ESP32 Devkit 3d model by Andrei Golyakov
• Credits for the SK6814mini 3d model by Laur V

Markdown tables

The Markdown tables were generated using the fabulous tool called tableconvert.