Breathe easy with accurate NO2 detection using 3SP-NO2-20 and STM32F031K6
Say NO to NO2 pollution
Published Oct 01, 2024
Click board™
NO2 Click
Dev. board
Nucleo 32 with STM32F031K6 MCU
Compiler
NECTO Studio
MCU
STM32F031K6
Our NO2 monitoring solution offers real-time data to individuals, cities, and industries, enabling them to combat nitrogen dioxide pollution for improved air quality
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Hardware Overview
How does it work?
NO2 Click is based on the 3SP-NO2-20 gas sensor from SPEC Sensors, which can sense NO2 concentration up to 20ppm. The sensor has a very short response time; however, the longer it is exposed to a particular gas, the more accurate data it can provide. This is especially true when calibration is performed. The sensor is sensitive to small dust particles, condensed water, and other impurities, which might prevent gas from reaching the sensor. It is advised to protect the sensor when used in critical applications. In ideal conditions, the lifetime of this sensor is indefinite, but in real-life applications, the expected operating life is more than five years (10 years at 23 ± 3 ˚C; 40 ± 10 %RH). Although very reliable and accurate, this sensor is great for building relative gas sensing applications. For example, it can detect an increased level of NO2 gas. However, when developing applications for the absolute gas concentration, the sensor must be calibrated, and the measurement data needs to be compensated. Factors such as humidity and temperature can affect measurements; the sensor reaction curve to a specific measured gas (nitrogen dioxide) is not completely linear, and other gases might affect the measurement (cross-sensitivity to other gases). For this reason, a range of calibration routines must be done in the working environment conditions to calculate the
absolute gas concentration. NO2 click uses the LMP91000, a configurable AFE potentiostat IC for low-power chemical sensing applications, from Texas Instruments. It provides the complete sensor solution, generating the output voltage proportional to the sensor current. A trans-impedance amplifier (TIA) with a programmable gain is used to convert the current through the sensor, covering the range from 5μA to 750 μA, depending on the used sensor. The voltage between the referent electrode (RE) and the working electrode (WE) is held constant, with the bias set by the variable bias circuitry. This type of sensor performs best when a fixed bias voltage is applied. The sensor manufacturer recommends a 200mV fixed bias for the sensor on this Click board™. The bias voltage and the TIA gain can be set via the I2C registers. In addition, an embedded thermal sensor in the AFE IC can be used for the result compensation if needed. It is available via the VOUT pin as the analog voltage value concerning GND. The Click board™ has two additional ICs onboard. The first is the MCP3221, a 12-bit successive approximation register A/D converter from Microchip. The second IC is the OPA344, a single-supply, rail-to-rail operational amplifier from Texas Instruments. It is possible to use the onboard switch, labeled as AN SEL, to select the IC to which the VOUT pin from the
LMP91000 AFE is routed. If the switch is in the ADC position, the VOUT pin will be routed to the input of the MCP3221 ADC. This allows the voltage value at the VOUT pin to be read via the I2C interface as digital information. When the switch is in the AN position, it will route the VOUT pin of the LMP91000 AFE IC to the input of the OPA344. The output of the OPA344 op-amp has a stable unity gain, acting as a buffer so that the voltage at the VOUT pin of the AFE can be sampled by the host MCU via the AN pin of the mikroBUS™. The RST pin on the mikroBUS™ is routed to the MEMB pin of the LMP91000, and it is used to enable the I2C interface section, thus making it possible to use more than one chip on the same I2C bus. When driven to a LOW logic level, the I2C communication is enabled, and the host device (host MCU) can issue a START condition. The RST pin should stay at LOW during the communication. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.
Features overview
Development board
Nucleo 32 with STM32F031K6 MCU board provides an affordable and flexible platform for experimenting with STM32 microcontrollers in 32-pin packages. Featuring Arduino™ Nano connectivity, it allows easy expansion with specialized shields, while being mbed-enabled for seamless integration with online resources. The
board includes an on-board ST-LINK/V2-1 debugger/programmer, supporting USB reenumeration with three interfaces: Virtual Com port, mass storage, and debug port. It offers a flexible power supply through either USB VBUS or an external source. Additionally, it includes three LEDs (LD1 for USB communication, LD2 for power,
and LD3 as a user LED) and a reset push button. The STM32 Nucleo-32 board is supported by various Integrated Development Environments (IDEs) such as IAR™, Keil®, and GCC-based IDEs like AC6 SW4STM32, making it a versatile tool for developers.
Microcontroller Overview
MCU Card / MCU
Architecture
ARM Cortex-M0
MCU Memory (KB)
32
Silicon Vendor
STMicroelectronics
Pin count
32
RAM (Bytes)
4096
You complete me!
Accessories
Click Shield for Nucleo-32 is the perfect way to expand your development board's functionalities with STM32 Nucleo-32 pinout. The Click Shield for Nucleo-32 provides two mikroBUS™ sockets to add any functionality from our ever-growing range of Click boards™. We are fully stocked with everything, from sensors and WiFi transceivers to motor control and audio amplifiers. The Click Shield for Nucleo-32 is compatible with the STM32 Nucleo-32 board, providing an affordable and flexible way for users to try out new ideas and quickly create prototypes with any STM32 microcontrollers, choosing from the various combinations of performance, power consumption, and features. The STM32 Nucleo-32 boards do not require any separate probe as they integrate the ST-LINK/V2-1 debugger/programmer and come with the STM32 comprehensive software HAL library and various packaged software examples. This development platform provides users with an effortless and common way to combine the STM32 Nucleo-32 footprint compatible board with their favorite Click boards™ in their upcoming projects.
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Click board™ Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the Nucleo 32 with STM32F031K6 MCU as your development board.
Track your results in real time
Application Output
1. Application Output - In Debug mode, the 'Application Output' window enables real-time data monitoring, offering direct insight into execution results. Ensure proper data display by configuring the environment correctly using the provided tutorial.
2. UART Terminal - Use the UART Terminal to monitor data transmission via a USB to UART converter, allowing direct communication between the Click board™ and your development system. Configure the baud rate and other serial settings according to your project's requirements to ensure proper functionality. For step-by-step setup instructions, refer to the provided tutorial.
3. Plot Output - The Plot feature offers a powerful way to visualize real-time sensor data, enabling trend analysis, debugging, and comparison of multiple data points. To set it up correctly, follow the provided tutorial, which includes a step-by-step example of using the Plot feature to display Click board™ readings. To use the Plot feature in your code, use the function: plot(*insert_graph_name*, variable_name);. This is a general format, and it is up to the user to replace 'insert_graph_name' with the actual graph name and 'variable_name' with the parameter to be displayed.
Software Support
Library Description
This library contains API for NO2 Click driver.
Key functions:
no2_enable- Device Enable functionno2_read_adc- Function for read ADC sensor datano2_get_no_2_ppm- Get NO2 Data function
Open Source
Code example
The complete application code and a ready-to-use project are available through the NECTO Studio Package Manager for direct installation in the NECTO Studio. The application code can also be found on the MIKROE GitHub account.
/*!
* \file
* \brief No2 Click example
*
* # Description
* This application measures NO2.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes I2C driver and device configuration.
*
* ## Application Task
* Gets NO2 (Nitrogen dioxide) data as ppm value and logs to USBUART every 500ms.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "no2.h"
// ------------------------------------------------------------------ VARIABLES
static no2_t no2;
static log_t logger;
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( void )
{
log_cfg_t log_cfg;
no2_cfg_t cfg;
/**
* Logger initialization.
* Default baud rate: 115200
* Default log level: LOG_LEVEL_DEBUG
* @note If USB_UART_RX and USB_UART_TX
* are defined as HAL_PIN_NC, you will
* need to define them manually for log to work.
* See @b LOG_MAP_USB_UART macro definition for detailed explanation.
*/
LOG_MAP_USB_UART( log_cfg );
log_init( &logger, &log_cfg );
log_info( &logger, "---- Application Init ----" );
// Click initialization.
no2_cfg_setup( &cfg );
NO2_MAP_MIKROBUS( cfg, MIKROBUS_1 );
no2_init( &no2, &cfg );
no2_default_cfg( &no2 );
log_printf( &logger, "NO2 is initialized \r\n" );
Delay_ms( 300 );
}
void application_task ( void )
{
float no2_value;
no2_value = no2_get_no_2_ppm( &no2 );
log_printf( &logger, "NO2 value : %.2f ppm \r\n", no2_value );
Delay_ms( 500 );
}
void main ( void )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
