Gain insight into the invisible forces of magnetism with MLX90393 and STM32F091RC
Unraveling the magnetic mysteries
Published Feb 26, 2024
Click board™
Gaussmeter click
Dev. board
Nucleo-64 with STM32F091RC MCU
Compiler
NECTO Studio
MCU
STM32F091RC
Explore the versatile world of gaussmeters and find out how these portable wonders can transform the way you measure, control, and understand magnetic fields
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Hardware Overview
How does it work?
Gaussmeter Click is based on the MLX90393, a micropower magnetometer based on the proprietary Triaxis® technology from Melexis. This IC is based on the Hall effect principle, which allows it to detect very small fluctuations in the magnetic field. The Hall sensor plates, featuring the patented IMC technology, are located in the center of the die, which is located in the center of the package. The measurement current, generated as a result of the Hall effect, is passed through the transimpedance amplifier (TIA) and sampled by the 19-bit A/D converter (ADC). The output is the truncated to 16-bits, by applying the bit-shifting operation, programmed by the user (RES_XYZ bits). This allows the range to be dynamically set, according to measurement conditions, leaving unused MSBs or LSBs out. Additionally, it is possible to set the TIA gain level in the range from 0 to 7 to best match the field strength. The value of the RES bits and the gain level both affect the sensitivity of the sensor. The MLX90393 datasheet contains a table with the RES and GAIN, and corresponding µT/LSB values. When required, it is possible to set the oversampling rate of the ADC decimation filter. This will provide less noise and more consistent readings. However, oversampling affects the data acquisition time, as the sampling process has to be repeated a number of times, depending on the oversampling rate. If the fast response is required, the oversampling and digital filtering functions
should be turned off. The measurement is affected by the temperature. Therefore, the MLX90393 is also equipped with the temperature sensor, used to provide the required measurements. The thermal sensitivity drift compensation can be enabled by the appropriate bit in the configuration register. Two sensitivity drift compensation factors can be used, one for temperatures greater than the reference and other for the temperatures lesser than the reference value. Wakeup on Change (WOC) mode is used to alert the MCU via the interrupt pin when certain conditions are met. It can be configured to trigger an interrupt on the INT pin if the difference between the reference measurement value and the current measurement value exceed a threshold defined by the user. The interrupt is reported on the INT pin of the IC, routed to the INT pin of the mikroBUS™, and/or on the INT/TRIG pin, routed to the mikroBUS™ PWM pin (labeled as TRG), if it is configured that way. The INT/TRIG pin can also be set as the trigger input, by configuring the corresponding bits (TRIG_INT_SEL and EXT_TRIG). These pins are active HIGH. Besides the WOC mode, there is also Burst and Single Measurement modes. Both of these modes can use the INT pin to signalize that there is a conversion data ready to be read. Once the MCU reads the data, the INT/Data Ready event will be cleared. The Burst mode provides data in programmed intervals, while Single Measurement
mode will provide one reading when commanded, signal it via the INT pin and revert to IDLE mode, consuming less power. The MLX90393 sensor contains 1KB of volatile (RAM) memory. This memory is used to store config parameters and register values, but also there are some free locations for storing user information, e.g. compensation values and similar. Besides 1KB of volatile memory, there is also 1KB of non-volatile memory. During the POR, the complete content of the NV memory is automatically copied to the RAM restoring the saved working parameters that way. There are also commands available for the user, in order to store to or restore RAM data from the non-volatile (NV) memory. However, it is not recommended to write to the NV memory area too often, as this type of memory has an inherently limited life cycle. This Click board™ allows both SPI and I2C communication protocols. To select a proper protocol, the SMD jumpers labeled as SEL COM should be moved to the appropriate position (I2C or SPI). Please note that both jumpers need to be at the same setting (both as SPI or both as I2C). The I2C address of the Click board™ is selectable by the onboard SMD jumpers, labeled as I2C ADDR. These two jumpers directly set the values of the LSB address of the IC. The 7-bit address of the device is 00011XXZ, where XX are the values set by these jumpers, while Z is the R/W bit.
Features overview
Development board
Nucleo-64 with STM32F091RC MCU offers a cost-effective and adaptable platform for developers to explore new ideas and prototype their designs. This board harnesses the versatility of the STM32 microcontroller, enabling users to select the optimal balance of performance and power consumption for their projects. It accommodates the STM32 microcontroller in the LQFP64 package and includes essential components such as a user LED, which doubles as an ARDUINO® signal, alongside user and reset push-buttons, and a 32.768kHz crystal oscillator for precise timing operations. Designed with expansion and flexibility in mind, the Nucleo-64 board features an ARDUINO® Uno V3 expansion connector and ST morpho extension pin
headers, granting complete access to the STM32's I/Os for comprehensive project integration. Power supply options are adaptable, supporting ST-LINK USB VBUS or external power sources, ensuring adaptability in various development environments. The board also has an on-board ST-LINK debugger/programmer with USB re-enumeration capability, simplifying the programming and debugging process. Moreover, the board is designed to simplify advanced development with its external SMPS for efficient Vcore logic supply, support for USB Device full speed or USB SNK/UFP full speed, and built-in cryptographic features, enhancing both the power efficiency and security of projects. Additional connectivity is
provided through dedicated connectors for external SMPS experimentation, a USB connector for the ST-LINK, and a MIPI® debug connector, expanding the possibilities for hardware interfacing and experimentation. Developers will find extensive support through comprehensive free software libraries and examples, courtesy of the STM32Cube MCU Package. This, combined with compatibility with a wide array of Integrated Development Environments (IDEs), including IAR Embedded Workbench®, MDK-ARM, and STM32CubeIDE, ensures a smooth and efficient development experience, allowing users to fully leverage the capabilities of the Nucleo-64 board in their projects.
Microcontroller Overview
MCU Card / MCU
Architecture
ARM Cortex-M0
MCU Memory (KB)
256
Silicon Vendor
STMicroelectronics
Pin count
64
RAM (Bytes)
32768
You complete me!
Accessories
Click Shield for Nucleo-64 comes equipped with two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the STM32 Nucleo-64 board with no effort. This way, Mikroe allows its users to add any functionality from our ever-growing range of Click boards™, such as WiFi, GSM, GPS, Bluetooth, ZigBee, environmental sensors, LEDs, speech recognition, motor control, movement sensors, and many more. More than 1537 Click boards™, which can be stacked and integrated, are at your disposal. The STM32 Nucleo-64 boards are based on the microcontrollers in 64-pin packages, a 32-bit MCU with an ARM Cortex M4 processor operating at 84MHz, 512Kb Flash, and 96KB SRAM, divided into two regions where the top section represents the ST-Link/V2 debugger and programmer while the bottom section of the board is an actual development board. These boards are controlled and powered conveniently through a USB connection to program and efficiently debug the Nucleo-64 board out of the box, with an additional USB cable connected to the USB mini port on the board. Most of the STM32 microcontroller pins are brought to the IO pins on the left and right edge of the board, which are then connected to two existing mikroBUS™ sockets. This Click Shield also has several switches that perform functions such as selecting the logic levels of analog signals on mikroBUS™ sockets and selecting logic voltage levels of the mikroBUS™ sockets themselves. Besides, the user is offered the possibility of using any Click board™ with the help of existing bidirectional level-shifting voltage translators, regardless of whether the Click board™ operates at a 3.3V or 5V logic voltage level. Once you connect the STM32 Nucleo-64 board with our Click Shield for Nucleo-64, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.
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-64 with STM32F091RC 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 Gaussmeter Click driver.
Key functions:
gaussmeter_write_reg- This function writes 16-bit data to the specified register addressgaussmeter_get_data- This function reads the temperature and axis data from the chipgaussmeter_digital_read_int- This function reads the digital input signal from the INT pin.
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 Gaussmeter Click example
*
* # Description
* This example showcases how to configure and use the Gaussmeter Click. This Click measures
* magnetic fields around the device using a 3 axis measurement system. Alongside the magnetometer,
* the Click contains an integrated temperature sensor which provides data for the thermal compensation.
*
* The demo application is composed of two sections :
*
* ## Application Init
* This function initializes and configures the Click and logger modules.
* Additional configuring is done in the default_cfg(...) function.
*
* ## Application Task
* This function reads data from the magnetometer and the temperature sensor and displays that
* data using the UART console every 400 milliseconds.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "gaussmeter.h"
// ------------------------------------------------------------------ VARIABLES
static gaussmeter_t gaussmeter;
static log_t logger;
static uint8_t buf_idx;
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( )
{
log_cfg_t log_cfg;
gaussmeter_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.
gaussmeter_cfg_setup( &cfg );
GAUSSMETER_MAP_MIKROBUS( cfg, MIKROBUS_1 );
gaussmeter_init( &gaussmeter, &cfg );
Delay_ms ( 100 );
gaussmeter_default_cfg( &gaussmeter );
Delay_ms ( 500 );
}
void application_task ( )
{
float temp_buf[ 4 ] = { 0 };
uint8_t error_bit;
uint8_t axis_check;
uint8_t cnt;
error_bit = gaussmeter_get_data( &gaussmeter, temp_buf );
if ( !error_bit )
{
axis_check = 1;
buf_idx = 0;
}
for ( cnt = 0; cnt < 4; cnt++ )
{
switch ( gaussmeter.aux.command_byte_low & axis_check )
{
case 1:
{
log_printf( &logger, " * Temperature: %.2f C\r\n", temp_buf[ buf_idx++ ] );
break;
}
case 2:
{
log_printf( &logger, " * X-axis: %.2f microT\r\n", temp_buf[ buf_idx++ ] );
break;
}
case 4:
{
log_printf( &logger, " * Y-axis: %.2f microT\r\n", temp_buf[ buf_idx++ ] );
break;
}
case 8:
{
log_printf( &logger, " * Z-axis: %.2f microT\r\n", temp_buf[ buf_idx++ ] );
}
}
axis_check <<= 1;
}
log_printf( &logger, "----------------------------------\r\n" );
Delay_ms ( 400 );
}
int main ( void )
{
/* Do not remove this line or clock might not be set correctly. */
#ifdef PREINIT_SUPPORTED
preinit();
#endif
application_init( );
for ( ; ; )
{
application_task( );
}
return 0;
}
// ------------------------------------------------------------------------ END
