NM-EPD-420 Factory Test Quick Start

This guide walks you through running the factory test firmware on the NM-EPD-420 board.

What This Firmware Does

The factory test firmware exercises every on-board peripheral in a fixed sequence (T0–T11), shows a result page on the EPD for every step, and lets the operator confirm or reject each step with the USER and BOOT buttons. At the end a one-page summary screen lists every test as PASS / FAIL / SKIP.

• Boots the board and initialises every peripheral driver
• Runs 10 hardware tests one after another
• Renders a dedicated screen for every test on the 3-color e-paper panel
• Plays audio tones and Beethoven's Ode to Joy through the ES8311 codec
• Records a short voice clip from the LMD4737 DMIC and computes RMS
• Probes I2C, scans Wi-Fi, mounts an SD card, talks to the LoRa modem
• Prints a structured summary on the EPD and a machine-parseable line on the serial port

A complete run typically takes ~3 minutes, dominated by EPD full-refresh time (~10 s per page on a 3-color panel).

Test Sequence

Test	Item	Description	Screen
T0	System startup	Serial / EPD init, welcome screen, wait USER
T1	EPD display	White / Black / Red fill + text demo (four-color SKU adds yellow fill / text)	—
T2	WS2812 RGB LED	RED → GREEN → BLUE → WHITE cycle
T3	Buttons	USER key and BOOT key press detection	—
T4	ES8311 codec	Sweep 500/1k/2k/3k Hz + Ode to Joy melody
T5	DMIC mic	Voice record + speaker loopback + RMS check
T6	AHT20 sensor	Temperature & humidity over I2C
T7	Battery ADC	Battery divider voltage (SKIP if not fitted)	—
T8	Wi-Fi scan	2.4 GHz AP scan, expect ≥ 1 network
T9	SD card R/W	FSPI mount + write / read-back verify
T10	LoRa SPI bus	Reset modem, check BUSY low	—
T11	Summary	Per-item PASS/FAIL/SKIP table + verdict

On the four-color SKU NM-EPD-420-4C, T1 checks white, black, red, and yellow full-screen fills followed by black / red / yellow text. Each full refresh takes about 25–30 seconds on this panel and partial refresh is not supported, so T1 takes noticeably longer than on the tri-color or black/white versions.

Operator Workflow

   power on
      │
      ▼
   ┌─────────────┐
   │ T0 Welcome  │ ──► press USER
   └─────────────┘
         │
         ▼
   ┌─────────────┐
   │ T1 – T10    │
   │ for each:   │
   │   show screen
   │   run hardware
   │   USER = PASS
   │   BOOT = FAIL
   └─────────────┘
         │
         ▼
   ┌─────────────┐
   │ T11 Summary │ ──► halt; power-cycle to retest
   └─────────────┘

Buttons are debounced (5 – 10 ms samples) and gated against EPD BUSY so a press during a refresh cannot be consumed as a verdict for the next test.

Build & Flash

Prerequisites: PlatformIO Core (or VS Code + PlatformIO extension).

# Clone the repository, then in repo root:
$env:IDF_GITHUB_ASSETS = "dl.espressif.cn/github_assets"   # optional, China mirror
pio run                                                    # build
pio run --target upload --upload-port COM38                # flash
pio device monitor --baud 115200                           # serial console

The commands above use the default nm-epd-420 environment (tri-color panel). For the four-color SKU NM-EPD-420-4C, select the nm-epd-420-4c build environment instead:

• pio run -e nm-epd-420-4c — build
• pio run -e nm-epd-420-4c --target upload --upload-port COM38 — flash

Or one-shot via VS Code tasks:

• Build (nm-epd-420)
• Upload (nm-epd-420)

The first build downloads the ESP-IDF toolchain (~hundreds of MB) into %USERPROFILE%\.platformio. Subsequent builds take ~25 s.

Serial Output Example

[FACTORY TEST] Board: NM-EPD-420
[FACTORY TEST] FW: v1.3.10
[FACTORY TEST] T0 - System startup OK
...
[FACTORY TEST] T1 START - EPD Display
[T1] Round 1/4 - Filling screen WHITE ...
[T1] BUSY self-check: sawHigh=1  highMs=2873
...
[FACTORY TEST] ===== SUMMARY =====
[FACTORY TEST] T1   EPD Display    [PASS]
[FACTORY TEST] T2   WS2812 RGB LED [PASS]
...
[FACTORY TEST] Overall: FACTORY_TEST=OK

Troubleshooting

Issue	Solution
sawHigh=0 on T1	Check BUSY-pin wiring (open net, cold solder joint, wrong GPIO)
EPD misbehaves after porting	Look at Display::resync() in src/ui/display_helper.h
No audio on T4	Verify PIN_PA_CTRL is HIGH and external PA is enabled
SD card fails on T9	Ensure HSPI pins (7–11) are not occupied by other functions
Wi-Fi scan empty on T8	Move closer to an AP or check antenna connection

Reference

• NM-EPD-420 GitHub Repository
• Product Overview