NRF52832-BME280-RADIO

Overview

A battery-powered wireless environmental sensor built around the Nordic nRF52832 and Bosch BME280. The radio link uses the nRF24L01(+)-compatible 2.4 GHz physical layer — nRF 2 Mbps GFSK, channel 99 (2479 MHz), 5-byte address 0xE7E7E7E7E7, 16-bit CRC and no data whitening. As a result, the transmitted packets can be received directly by:

• any nRF24L01 / nRF24L01+ module (or compatible clone) configured with the same channel, address and CRC, and
• any other nRF52832 (or nRF52-family) device running the matching RADIO configuration (Nrf_2Mbit, channel 99, address 0xE7E7E7E7E7, 16-bit CRC).

See Radio Protocol for the exact packet layout.

Features

• Register-level, non-blocking peripheral drivers (TWI, RADIO, SAADC, RTC, TEMP)
• Fully compensated BME280 readings using int64 arithmetic
• SAADC VDD monitoring — 12-bit, 64x oversampling, offset calibration
• nRF52 on-chip die temperature measurement
• 60-second periodic transmission interval (RTC2-driven)
• System ON idle with __WFE() sleep between cycles; HFCLK gated off
• Optional UART debug output (-DUSE_UART, 9600 baud, P0.06)
• Errata workarounds applied: PAN_028 #29, #30, #31

Hardware Specification

Component	Detail
MCU	Nordic nRF52832 (ARM Cortex-M4F @ 64 MHz)
Sensor	Bosch BME280 (I²C address 0x76)
Radio	2 Mbps GFSK, channel 99 (2479 MHz), +4 dBm TX
TX Period	60 seconds (RTC2 CC[0] = 983 040 ticks)
Power	2× AA / Li-Po, measured via SAADC VDD input

Pin Assignment

Signal	Pin	Notes
SDA	P0.26	TWI1, 400 kHz
SCL	P0.27	TWI1
UART TX	P0.06	Optional, 9600 8N1

Radio Protocol — Packet Format

The parameters below are chosen to be wire-compatible with the nRF24L01(+) modules (no data whitening, standard 16-bit CRC, default address 0xE7E7E7E7E7), so the same packet can also be received by another nRF52832 configured identically. Note: this firmware accesses the RADIO peripheral directly and does not require (or use) a Nordic SoftDevice, so the receiving nRF52 device must likewise run bare-metal (or without an active SoftDevice) to control RADIO the same way.

10-byte payload transmitted as a single RADIO packet (2Mbit mode, 16-bit CRC):

Offset	Size	Field	Description
0	1	Length	Payload length, fixed to 10
1	1	Seq ID	Rolling counter, bit 0 always set
2	3	Pressure	Compensated pressure, Pa (24-bit)
5	1	Die Temp	nRF52 junction temperature, °C ÷ 4
6	2	Temp	BME280 temperature, 0.01 °C
8	2	Humidity	BME280 relative humidity, 0.1 %RH
10	2	Voltage	VDD battery, 3600 / 4095 mV per LSB

Address field: base 0xE7E7E7E7, prefix 0xE7 (full address 0xE7E7E7E7E7).

Firmware Architecture

+----------+    +----------+    +-----------+    +-----------+    +-----------+
|  CLOCK   |--->|   TWI1   |--->|  BME280   |--->|Compensate |--->|  RADIO    |
| HFXO/LFXO|    | SDA/SCL  |    | 0x76 I2C  |    | int64_t   |    | ch.99 2M  |
+----------+    +----------+    +-----------+    +-----------+    +-----------+
                                                     |
                                               +-----v------+
                                               |   SAADC    |
                                               |  VDD meas  |
                                               +------------+
                                                     |
                                               +-----v------+
                                               |   TEMP     |
                                               | die temp   |
                                               +------------+
                                                     |
                                               +-----v------+
                                               |   RTC2     |
                                               | 60 s wake  |
                                               +------------+

Getting Started

Prerequisites

• ARM GCC toolchain (arm-none-eabi-gcc) >= 9-2020-q2-update
• GNU Make
• (Optional) nRF5x command-line tools for flashing: nrfjprog

Build & Flash

$ make
$ make jflash                # nRF52-DK / J-Link
$ make stflash               # ST-LINK (ST-LINK_CLI.exe)

UART Debug

Define USE_UART at build time to enable formatted output on P0.06 (9600 baud):

$ make CFLAGS="-DUSE_UART"

Supported IDEs

IDE	Project path
SEGGER Embedded Studio	IDE/ses/
IAR EWARM	IDE/EWARM/
Keil MDK-ARM (uVision)	IDE/MDK-ARM/

Project Structure

+-- main.c                 Application entry point and main loop
+-- Makefile               GCC build system
+-- .travis.yml            CI configuration
+-- LICENSE                MIT License
+-- drv/
|   +-- inc/               CMSIS-CORE + nRF52 register definitions
|   |   +-- CMSIS/         core_cm4.h, cmsis_gcc.h, cmsis_iccarm.h
|   |   +-- nrf.h          Master MCU header selector
|   |   +-- nrf52.h        nRF52832 peripheral struct definitions
|   |   +-- nrf52_bitfields.h  Bit-field enumerations (SVD-generated)
|   +-- src/
|       +-- gcc_startup_nrf52.S  Reset vector, data/BSS init
|       +-- system_nrf52.c       SystemInit, errata workarounds
|       +-- iar_startup_nrf52.s  IAR startup
+-- IDE/
    +-- ses/               SEGGER Embedded Studio project
    +-- EWARM/             IAR Embedded Workbench project
    +-- GCC/               Linker script + Makefile templates
    +-- MDK-ARM/           Keil uVision project

Known Errata Workarounds

Anomaly	Description	Workaround
PAN_028 #29	TEMP STOP clears register	Read TEMP before TASKS_STOP
PAN_028 #30	TEMP AFE not powered down	Explicit TASKS_STOP after DATARDY
PAN_028 #31	TEMP offset uninitialized	Manual load to 0x4000C504

License

Distributed under the MIT License. See LICENSE for details.