PCB pin trace

Source: the user's EasyEDA PCB JSON (editorVersion: 6.5.51, XIAO reference U8), provided on 2026-09-27. GPIO translations were checked against the installed Arduino XIAO_ESP32C3 pins_arduino.h. Top/bottom refer to the PCB drawing's Y axis.

Signal	PCB net / connection	XIAO label	ESP32-C3 GPIO
Upper button, S2 (Y=3249.5)	S2.2 -> U8_3 -> U8 pad 3	D2/A2	4
Lower button, S1 (Y=3290)	S1.1 -> U8_2 -> U8 pad 2	D1/A1	3
RTC SDA	U7_SDA -> U8 pad 5	SDA/D4	6
RTC SCL	U7_SCL -> U8 pad 6	SCL/D5	7
EPD SCK	U5_4 -> U8 pad 9	SCK/D8	8
EPD MOSI	U5_3 -> U8 pad 11	MOSI/D10	10
EPD CS	U5_5 -> U8 pad 4	D3/A3	5
EPD DC	U5_6 -> U8 pad 8	RX/D7	20
EPD RST	U5_7 -> U8 pad 7	TX/D6	21
EPD BUSY	U5_8 -> U8 pad 10	MISO/D9	9

Both buttons close to GND. R1 (100 kOhm) pulls U8_2 to VCC, and R2 (100 kOhm) pulls U8_3 to VCC. Firmware also enables the requested internal pull-ups. XIAO pad numbers are footprint terminal numbers, not GPIO numbers.

Upper button / buzzer conflict

Assembly clarification: the user confirmed that this is an older design and U3 is not fitted. The loading concern below does not apply to that assembly.

U3 (GSC4417YA-16R4000) pad 1 is on U8_3, and pad 2 is GND. The routed trace from U3 pad 1 at (4024.61, 3344.5) joins S2's net at (4033.126, 3323.151). Thus the buzzer and upper button share the same GPIO-to-ground path; this is more than a duplicate net label in the footprint. If fitted, the buzzer may load the pull-up and keep GPIO4 LOW even with S2 released.

Check the USB raw-input logs first. If GPIO4 stays LOW, power off and isolate U3 before retesting the button. Do not drive GPIO4 HIGH to test it: pressing the button would short that output to ground. A board revision should separate the button input from a suitable buzzer driver/output.

This trace establishes the design's connections, not solder continuity on the assembled board. It does not diagnose the reported RTC/display freeze; USB logs now distinguish RTC seconds, loop progress, and display BUSY waits.