NM-EPD-420
Overview
The NM-EPD-420 is an ESP32-S3 based 4.2-inch e-ink display development board. It is available with either a tri-color (Black / White / Red) e-paper panel or a dual-color (Black / White) e-paper panel, and features an audio codec (ES8311), environmental sensor (AHT20), RGB LED (WS2812), SD card slot, and optional LoRa modem (SX126x family) — making it ideal for low-power IoT dashboards, outdoor signage, and smart labeling applications.
Hardware Specifications
Core
| Item | Specification |
|---|---|
| MCU | ESP32-S3 (dual-core Xtensa LX7 @ 240 MHz) |
| Flash | 16 MB |
| PSRAM | 8 MB (QIO OPI) |
| Wireless | Wi-Fi 4 (802.11 b/g/n) + Bluetooth 5 LE |
Display
| Item | Specification |
|---|---|
| Panel | GDEY042Z98 tri-color e-paper (or GYE042A87 black/white e-paper), same pinout |
| Size | 4.2 inches |
| Resolution | 400 × 300 |
| Colors | 3-color (Black / White / Red) or 2-color (Black / White) |
| Driver | GxEPD2 |
| Interface | SPI (FSPI) |
The NM-EPD-420 currently supports both the tri-color panel (GDEY042Z98) and the black/white panel (GYE042A87). Their refresh performance differs as follows:
-
GDEY042Z98 Tri-color E-Paper:
- SKU: NM-EPD-420
- Full refresh (Black / White / Red) takes about 10 seconds; partial refresh is not supported.
- For weather stations, dashboards, and similar applications, the tri-color panel provides richer visual effects but slower refresh speeds, making it suitable for static content display.
- The default tri-color version does not include a LoRa module and is ideal for general desktop applications.
-
GYE042A87 Black/White E-Paper:
- SKU: NM-EPD-420-BW
- Full refresh (Black / White) takes about 2–3 seconds; partial refresh is supported, with partial refresh time around 1 second.
- For applications requiring faster content updates, the black/white panel (GYE042A87) is recommended.
- The NM-EPD-420-BW version supports a LoRa module by default, making it more convenient for indoor desktop LoRa node applications.
The LoRa version includes an HT-RA62 module (SX1262) for Meshtastic, MeshCore, and other LoRa applications. The non-LoRa version omits the module for general applications. The default NM-EPD-420-BW version supports LoRa to provide better screen refresh performance for relevant LoRa applications.
Onboard Peripherals
| Block | Part | Interface | Notes |
|---|---|---|---|
| Codec | ES8311 | I2C 0x18 + I2S | DAC → external PA → 8 Ω speaker |
| Microphone | LMD4737 PDM DMIC | I2S (DMIC mode) | 16 kHz sample rate |
| T/RH Sensor | AHT20 | I2C 0x38 | Power-gated via PIN_TEMP_CTL |
| RGB LED | WS2812 | RMT | 1 pixel |
| SD Card | μSD | SPI (HSPI) | Shared bus with LoRa |
| LoRa Modem | SX126x family | SPI (HSPI) | CS / RST / BUSY GPIOs |
| Buttons | USER, BOOT | GPIO | Active LOW, external pull-up |
| Audio Amp | External Class-D | EN GPIO | Enabled by PIN_PA_CTRL HIGH |
Pinout
EPD (FSPI)
| Signal | GPIO | Direction |
|---|---|---|
| SCK | 2 | OUT |
| MOSI | 1 | OUT |
| MISO | - | - |
| CS | 46 | OUT |
| DC | 4 | OUT |
| RST | 5 | OUT |
| BUSY | 6 | IN |
SD + LoRa (HSPI)
| Signal | GPIO | Direction |
|---|---|---|
| SCK | 9 | OUT |
| MOSI | 10 | OUT |
| MISO | 11 | IN |
| SD CS | 7 | OUT |
| LoRa NSS | 8 | OUT |
| LoRa RST | 12 | OUT |
| LoRa BUSY | 13 | IN |
| LoRa DIO1 | 14 | IN |
I2S (ES8311)
| Signal | GPIO | Direction |
|---|---|---|
| MCLK | 21 | OUT |
| BCLK | 15 | OUT |
| LRCK / WS | 17 | OUT |
| DOUT (ESP→DAC) | 18 | OUT |
| DIN (ADC→ESP) | 16 | IN |
I2C + Others
| Signal | GPIO | Direction | Notes |
|---|---|---|---|
| SDA | 39 | I/O | AHT20 + ES8311 shared bus |
| SCL | 38 | OUT | |
| TEMP_CTL | 40 | OUT | AHT20 power gate (HIGH = on) |
| PA_CTRL | 41 | OUT | External amplifier enable |
| USER button | 45 | IN | Active LOW |
| BOOT button | 0 | IN | Active LOW, RTC GPIO |
| LoRa EN | 47 | OUT | LoRa module power enable, active HIGH |
| Codec EN | 44 | OUT | Audio codec power enable, active HIGH |
| ADC EN | 43 | OUT | ADC module power enable, active HIGH |
| BATT_ADC | 3 | IN | Battery voltage divider sampling input |
Authoritative source: src/config.h