ESP32 BACnet MS/TP WiFi Display. 86 BACnet Objects

ESP32-based BACnet/IP device with ST7789 TFT display featuring 86 BACnet objects: 40 Analog Values, 40 Binary Values, 2 Analog Inputs, 2 Binary Inputs, and 2 Binary Outputs (expandable).

It can simultaneously connect the BACnet device through WiFi (BACnet/IP), WiFi to Ethernet bridge, and MS/TP (RS485 using a MAX485 module).

You can easily add extra BACnet objects and map them to ESP32 GPIO for analog and digital inputs/outputs.

Features

BACnet/IP Protocol: Full BACnet/IP stack implementation
BACnet MS/TP: RS485 MS/TP support alongside BACnet/IP (dual stack)
Live Display: Real-time monitoring of BACnet objects on 170x320 TFT display
86 BACnet Objects:
- 40 Analog Values (AV1-40) - read/write with COV and NVS persistence
- 40 Binary Values (BV1-40) - read/write with COV and NVS persistence
- 2 Analog Inputs (AI1-2) - sensor inputs with COV and NVS persistence
- 2 Binary Inputs (BI1-2) - binary states with COV and NVS persistence
- 2 Binary Outputs (BO1-2) - writable control outputs with COV and NVS persistence
Writable Metadata: Object Name and Description are writable for AV/BV/AI/BI/BO
WiFi Connectivity: ESP32 with built-in WiFi for BACnet/IP communication
Arduino Framework: Leverages Arduino ecosystem for easy hardware control
Change of Value (COV): Implements BACnet COV notifications for efficient real-time updates
Persistent Storage: Attribute values modifiable from BACnet supervisor are automatically saved to ESP32 non-volatile memory (NVS) for retention across power cycles
NVS Override: When USER_OVERRIDE_NVS_ON_FLASH=1, NVS is erased on boot and all values reset to defaults
Centralized Configuration: User settings are centralized in main/User_Settings.c

Photos

Hardware Requirements

Microcontroller: ESP32-WROOM-32
- CPU: Xtensa dual-core LX6, up to 240 MHz
- RAM: 520 KB SRAM (internal)
- ROM: 448 KB (bootloader & libraries)
- Flash: 4 MB integrated SPI flash
  - App partition: 1 MB (see partitions.csv)
  - NVS partition: 64 KB (BACnet object persistence)
- WiFi: 802.11 b/g/n, 2.4 GHz
- GPIO: 34 programmable pins
- ADC: 12-bit SAR, up to 18 channels
- UART: 3× (UART0 = USB debug, UART2 = MS/TP RS485)
- SPI: 4× (VSPI used for TFT display)
- Operating voltage: 3.3 V (USB 5 V via onboard regulator)
Display: ST7789 SPI TFT (170x320 pixels)
Display Connections:
- MOSI: GPIO 23
- SCLK: GPIO 18
- CS: GPIO 15
- DC: GPIO 2
- RST: GPIO 4
- BL (Backlight): GPIO 32

Hardware Components

ST7789 TFT Display

Resolution: 170x320 pixels
Interface: SPI (4-wire)
Driver: Custom TFT_eSPI component with offset calibration for clone displays

WiFi Connectivity

Built-in ESP32 WiFi for BACnet/IP communication
Configured via main/User_Settings.c
Static IP option in main/User_Settings.c. Set USER_WIFI_USE_STATIC_IP to 1 or 0

BACnet MS/TP (RS485)

Transceiver: MAX485 or equivalent RS485 converter
UART: UART2
Connections:
- DI (TX) → ESP32 GPIO17
- RO (RX) → ESP32 GPIO16
- DE/RE → ESP32 GPIO5
Baud Rate: 38400 (default)
MS/TP Settings: MAC 7, Max Master 127, Max Info Frames 80
Discovery: Some controllers (e.g., NAE) require manual add on the MS/TP field bus

GPIO Summary

Pin	Component	Signal	Definition
GPIO 2	TFT Display	DC (Data/Command)	components/TFT_eSPI/User_Setup.h
GPIO 4	TFT Display	RST (Reset)	components/TFT_eSPI/User_Setup.h
GPIO 15	TFT Display	CS (Chip Select)	components/TFT_eSPI/User_Setup.h
GPIO 18	TFT Display	SCLK (SPI Clock)	components/TFT_eSPI/User_Setup.h
GPIO 23	TFT Display	MOSI (SPI Data)	components/TFT_eSPI/User_Setup.h
GPIO 32	TFT Display	BACKLIGHT	components/TFT_eSPI/User_Setup.h
GPIO 16	MAX485	RO (RX)	main/mstp_rs485.c
GPIO 17	MAX485	DI (TX)	main/mstp_rs485.c
GPIO 5	MAX485	DE/RE	main/mstp_rs485.c

Build Requirements

ESP-IDF v5.5.1
Python 3.11+
xtensa-esp-elf toolchain

Building

cd BACnet-ESP32-86objects
idf.py build

Flashing

idf.py flash -p COM3

Or use the provided build/flash tasks in VS Code.

Monitoring Serial Output

idf.py monitor -p COM3

Configuration

Display Offset Calibration

The ST7789 display has a framebuffer offset that's compensated in components/TFT_eSPI/User_Setup.h:

#define TFT_OFFSET_X 0   // Horizontal offset
#define TFT_OFFSET_Y 0   // Vertical offset

Legacy TFT_COLSTART/TFT_ROWSTART examples are also present in comments in the same file; use one offset method consistently.

FreeRTOS Configuration

Arduino framework requires FreeRTOS tick rate of 1000Hz. This is set in sdkconfig:

CONFIG_FREERTOS_HZ=1000

User Settings (Centralized Configuration)

Most user-configurable settings are centralized in main/User_Settings.c and declared in main/User_Settings.h, including:

WiFi SSID/password and static IP settings
BACnet Device Instance and BBMD registration
BACnet/IP and MS/TP enable flags (USER_ENABLE_BACNET_IP, USER_ENABLE_BACNET_MSTP)
MS/TP parameters (MAC, baud rate, max master, max info frames)
Default object names, descriptions, units, and initial values

BACnet Object Configuration

Analog Values (AV1-40): Configure names, descriptions, units, and initial values in main/User_Settings.c
Binary Values (BV1-40): Configure names, descriptions, active/inactive text, and initial states in main/User_Settings.c
Analog Inputs (AI1-2): Configure names, descriptions, units, and COV increments in main/User_Settings.c. Read-only inputs suitable for sensor integration.
Binary Inputs (BI1-2): Configure names, descriptions, active/inactive text in main/User_Settings.c. Read-only binary states.
Binary Outputs (BO1-2): Configure names, descriptions, active/inactive text, and initial states in main/User_Settings.c. Writable control outputs with priority support.

Architecture

Components

components/bacnet-stack - BACnet/IP stack (modified from bacnet-stack/bacnet-stack)
components/TFT_eSPI - TFT graphics library
main - Application code
- main.c - BACnet initialization and main loop
- analog_value.c/h - Analog Value object creation and NVS persistence
- binary_value.c/h - Binary Value object creation and NVS persistence
- analog_input.c/h - Analog Input object creation and NVS persistence
- binary_input.c/h - Binary Input object creation and NVS persistence
- binary_output.c/h - Binary Output object creation and NVS persistence
- display.cpp - TFT display driver
- wifi_helper.c - WiFi configuration helpers

Display Layout

Item	Type	Display
AV1	Analog Value	Numeric (1 decimal)
AV2	Analog Value	Numeric (1 decimal)
AV3	Analog Value	Numeric (1 decimal)
AV4	Analog Value	Numeric (1 decimal)
BV1	Binary Value	ON/OFF + Status Dot (Blue=OFF, Green=ON)
BV2	Binary Value	ON/OFF + Status Dot (Blue=OFF, Green=ON)
BV3	Binary Value	ON/OFF + Status Dot (Blue=OFF, Green=ON)
BV4	Binary Value	ON/OFF + Status Dot (Blue=OFF, Green=ON)

BACnet Integration

The device broadcasts its Device ID and manages BACnet objects that can be read/written by any BACnet/IP or BACnet MS/TP client (e.g., YABE, Tridium Niagara, Metasys).

BACnet Objects Exposed

Device: Configurable in main/User_Settings.c
Analog Values: Instance 1-40
Binary Values: Instance 1-40
Analog Inputs: Instance 1-2
Binary Inputs: Instance 1-2
Binary Outputs: Instance 1-2

Modifications to bacnet-stack

This project uses the official bacnet-stack with the following modifications:

components/bacnet-stack/ - Configured as ESP-IDF component
Simplified for embedded systems (reduced features, optimized for ESP32)
WiFi-based BACnet/IP instead of Ethernet

For a list of specific changes, see BACNET_STACK_CHANGES.md (if available).

Development Notes

Display Boundary Constants

The display code uses boundary constants for easy layout modification:

#define DISP_X0    17      // Left edge
#define DISP_Y0    40      // Top edge
#define DISP_X1    151     // Right edge
#define DISP_Y1    278     // Bottom edge
#define DISP_WIDTH 135
#define DISP_HEIGHT 239

Position all elements relative to these constants to avoid hardcoding coordinates.

Troubleshooting

Display offset issues

If text appears misaligned, adjust TFT_OFFSET_X and TFT_OFFSET_Y in components/TFT_eSPI/User_Setup.h and recompile.

WiFi connection fails

Check SSID/password in main/User_Settings.c, then verify WiFi init/connection flow in main/wifi_helper.c.

Linker errors with Arduino

Ensure CONFIG_FREERTOS_HZ=1000 is set in sdkconfig and rebuild with idf.py fullclean && idf.py build.

Name		Name	Last commit message	Last commit date
Latest commit History 2 Commits
.devcontainer		.devcontainer
components		components
docs		docs
main		main
.clangd		.clangd
.gitignore		.gitignore
CMakeLists.txt		CMakeLists.txt
LICENSE		LICENSE
OBJECTS_CONFIGURATION.md		OBJECTS_CONFIGURATION.md
README.md		README.md
SETUP.md		SETUP.md
dependencies.lock		dependencies.lock
partitions.csv		partitions.csv
sdkconfig		sdkconfig

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ESP32 BACnet MS/TP WiFi Display. 86 BACnet Objects

Features

Photos

Hardware Requirements

Hardware Components

ST7789 TFT Display

WiFi Connectivity

BACnet MS/TP (RS485)

GPIO Summary

Build Requirements

Building

Flashing

Monitoring Serial Output

Configuration

Display Offset Calibration

FreeRTOS Configuration

User Settings (Centralized Configuration)

BACnet Object Configuration

Architecture

Components

Display Layout

BACnet Integration

BACnet Objects Exposed

Modifications to bacnet-stack

Development Notes

Display Boundary Constants

Troubleshooting

Display offset issues

WiFi connection fails

Linker errors with Arduino

References

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