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Compiled by: Wang Tongxue
LED dice schematic and PCB were drawn using Eagle. To avoid making the cube too large, only two different PCBs were designed: the power board and the MCU control board. Both PCBs are square with a dimension of 25mm x 25mm.
The power board has a charging circuit and a lithium battery socket, while the MCU control board has the main control chip, ADXL345 gyroscope, and necessary power management circuits. All LEDs draw power directly from the lithium battery, and the MCU is powered by the LDO MCP1700, while the lithium battery charging chip is the MCP73831. There is one complete power board and MCU board (i.e., all components soldered on both sides), while the other 4 PCBs are power boards with only LEDs soldered.
The uniqueness of these PCBs lies in the serrated holes on both sides, with three through holes on each side (cut in half for easy soldering for electrical connections, as shown in the image). On one hand, these holes make the physical object look more like a cube and keep everything in place; on the other hand, they transmit power signals and WS2812 control signals, distributing the three signals + 5V, GND, and LED control signals throughout the cube. The sequence of the PCBs is shown in the figure below. This is a flat layout of a cube, where edges of the same color indicate they are connected in the physical object. Arrows indicate the direction of WS2812 control signal transmission.
Assembling the cube is not easy, but to make it easier, a small soldering aid tool is used to solder at least three of the six PCBs together. Doing this twice will yield two PCB edges, and once everything is normal, they must be connected. Before soldering the lithium battery socket, make sure to solder the three PCBs together. Otherwise, you will have to modify the holes in the .stl file to fit the battery socket.
When the dice starts working, WiFi is not enabled to save some power, which is called modem-sleep. Checking the ESP datasheet shows that the MCU consumes only 15mA in modem-sleep mode, while it requires 70mA in normal mode, making this mode suitable for battery-powered devices. Therefore, before calling the setup function, the following code is needed:
void preinit() { ESP8266WiFiClass::preinitWiFiOff(); }
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