Heltec T114 — Bare-bones PlatformIO Template

A minimal PlatformIO Arduino project for the Heltec Mesh Node T114 (nRF52840 + SX1262). The T114 is not in PlatformIO's official board registry and there is almost no documentation on setting one up outside of the Meshtastic firmware. This repo extracts exactly what is needed to get a clean standalone project running.

This template targets the variant without GPS and without TFT screen. If you need to build for these, check the meshtastic variant files for these versions.

What's working from the VSCode PlatformIO Extension?

• Build
• Upload
• Monitor

An example main.cpp is provided which inits LoRa, flashes the neopixel and prints hello to serial. Also ships with RadioLib by default for the SX1262.

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Hardware

MCU	Nordic nRF52840 (Cortex-M4F, 64 MHz)
Radio	Semtech SX1262
Flash	MX25R1635F QSPI (2 MB)
RGB LEDs	2× WS2812B (NeoPixel)
Button	1× user button
Bluetooth	BLE 5.0 (integrated)
USB	USB-C, CDC serial + UF2 bootloader

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Prerequisites

1. PlatformIO — CLI or VS Code extension
2. Python 3 — required by PlatformIO's build scripts
3. nrfutil — only needed for USB serial flashing (not needed for UF2 drag-and-drop)

   pip install nrfutil
   

4. The board must have the Adafruit nRF52 bootloader flashed. Factory T114 units ship with it.

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Quick Start

git clone https://github.com/Nateyo/Heltec-T114-PlatformIO-Base
cd Heltec-T114-PlatformIO-Base
pio run

PlatformIO will automatically download the platform, BSP, and libraries on first build.

Build output is in .pio/build/heltec-mesh-node-t114/:

File	Use
firmware.uf2	Drag-and-drop flash via USB
firmware.hex	Flash via JLink / nrfjprog
firmware.bin	Raw binary

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Flashing

Option A — UF2 (manual drag-and-drop)

1. Double-tap the reset button. The board mounts as a USB drive.
2. Drag firmware.uf2 onto the drive.
3. The board reboots automatically into your firmware.

Option B — nrfutil via USB (easiest!)

pio run --target upload

This uses the nrfutil DFU protocol over USB serial. The bootloader is not touched.

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Serial Monitor

pio device monitor

Or use the PlatformIO IDE serial monitor. Baud rate is 115200.

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Pin Reference

LoRa (SX1262) — SPI0

Signal	Pin
CS / NSS	P0.24
DIO1	P0.20
BUSY	P0.17
RESET	P0.25
MISO	P0.23
MOSI	P0.22
SCK	P0.19

DIO2 is wired internally as the RF switch. DIO3 drives the TCXO at 1.8 V. Neither should be driven from the MCU.

I²C

Bus	SDA	SCL	Notes
Wire (0)	P0.26	P0.27	RTC footprint — unpopulated on V1
Wire1 (1)	P0.16	P0.13	Header pins, general use

Other

Function	Pin
Green LED (active-low)	P1.03
NeoPixel data	P0.14
User button	P1.10
Battery ADC	P0.04 (AIN2)
ADC enable	P0.06 (drive HIGH to enable divider)
QSPI SCK	P1.14
QSPI CS	P1.15
UART1 RX	P1.07
UART1 TX	P1.05

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Using the LoRa Radio

RadioLib is included as a dependency. The pin constants from variant.h map directly to RadioLib's Module constructor:

#include <RadioLib.h>

SX1262 radio = new Module(SX126X_CS, SX126X_DIO1, SX126X_RESET, SX126X_BUSY);

void setup() {
    // 915 MHz, 10 dBm, BW 125 kHz, SF 7, CR 4/5
    int state = radio.begin(915.0, 125.0, 7, 5, RADIOLIB_SX126X_SYNC_WORD_PRIVATE, 10);
}

Change 915.0 to 868.0 for EU868 or 923.0 for AS923.

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Project Structure

t114/
├── boards/
│   └── heltec_mesh_node_t114.json   # Board definition (not in PlatformIO registry)
├── variants/
│   └── heltec_mesh_node_t114/
│       ├── variant.h                # Pin definitions
│       └── variant.cpp              # Pin map + hardware init
├── extra_scripts/
│   └── nrf52_uf2.py                 # Post-build: .hex → .uf2
├── bin/
│   └── uf2conv.py                   # UF2 conversion utility
├── src/
│   └── main.cpp                     # Your application
└── platformio.ini

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Why a Custom BSP?

The platform_packages entry in platformio.ini uses Meshtastic's fork of the Adafruit nRF52 Arduino BSP rather than the upstream version. The fork is needed because:

• The upstream BSP does not include the heltec_mesh_node_t114 variant
• It adds C++17 compiler support (-std=gnu++17)
• It carries the correct SoftDevice (S140 v6.1.1) and linker configuration for this board

The fork tracks upstream closely. You can follow its commit history to assess drift.

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License

Variant files carry the original LGPL-2.1 header from the Adafruit nRF52 Arduino BSP.
bin/uf2conv.py is sourced from the Meshtastic firmware repository.
Everything else in this repo is released under MIT.