Digi Xbee3 Cellular to Pressure Sensor with MicroPython

ScottRaeker · March 3, 2021, 9:59pm

Introduction

Off the shelf hardware is used to demonstrate integrating an absolute barometric pressure sensor with Digi International’s LTE-M/NB-IoT cellular smart modem. The project utilizes the XB3-C-A2-UT-001 mounted in an XBIB-U-DEV eval board wired to a Mikroelektronika Pressure 4 Click board over I2C. MicroPython example code is provided for the XBee3 smart modem to communicate with the Pressure 4 Click temperature sensor over I2C… Mikroelektronika’s Pressure 4 Click™ board uses Bosch Sensortec’s BMP280 barometric pressure/temperature sensor.

Hardware Requirements

XB3-C-A2-UT-001 Digi XBee3 LTE-M/NB-IoT Cellular Smart Modem at Digi-Key
Mikroelektronika Pressure 4 Click™ board at Digi-Key

Accessories

Digi International XBIB-U-DEV eval board at Digi-Key (note: male pin headers soldered to XBIB-U-DEV board 20 pin header to facilitate wiring)

Supplier Documentation

Digi International XBee3 Cellular LTE-M/NB-IoT User Guide
Digi International Digi MicroPython Programming Guide
Digi International XBIB-U-DEV Reference Guide
Digi International XBIB-U-DEV Schematic
Mikroelektronika Pressure 4 Click™ board
Bosch Sensortec BMP280 datasheet
:

Hardware Setup

Pressure 4 Click Board

1 -	16 -
2 -	15 -
3 -	14 -
4 -	13 -
5 -	12 - SCL
6 -	11 - SDA
7 - +3.3V	10 -
8 - GND	9 - GND

XB3 20 pin header

1 - +3.3V	20 -
2 -	19 - SCL
3 - NC	18 -
4 - NC	17 -
5 - NC	16 -
6 - NC	15 -
7 - SDA	14 -
8 -	13 -
9 -	12 -
10 - GND	11 -

Wiring Diagram

Example Code

github.com

eewiki/Xbee3-MicroPython/blob/master/samples/pressure4click.py

# Micropython code example for Digi International Xbee3
# cellular module interface to Bosch BMP280 based
# Mikroelektronika Pressure 4 Click board barometric sensor 
# sensor 
#
# Wiring Diagram:
# XBee ->  Pressure 4 Click
#  19  SCL  12 
#   7  SDA  11 
#   1  Vcc  7 (+3.3V)
#  10  GND  8,9 


import utime
import ustruct
import machine


# set i2c clock to 100KHz
# Bosch i2c adress = 1110110 (0x76)

This file has been truncated. show original

Description

MicroPython code that runs on a Xbee 3 cellular module connected to a Pressure 4 Click board over I2C. The example code scans the I2C bus and prints active addresses, reads/prints the BMP280 chip id; writes the BMP280 data acquisition settings, reads/prints the calibration parameters and reads/prints pressure and temperature in a continuous loop.

Bosch Sensortec BMP280 Pressure and Temperature Calculation Background

Configuration settings and calculations used are based on section 3.12 of revision 1.19 of the BMP280 datasheet. Below table is from the datasheet.