Set a new standard for multifunctional testing with MCP3204 and STM32F446RE
Explore our multimeter's versatile measurement capabilities
Published Oct 08, 2024
Click board™
Multimeter Click
Dev Board
Nucleo 64 with STM32F446RE MCU
Compiler
NECTO Studio
MCU
STM32F446RE
Experience a new level of convenience and accuracy with our comprehensive multimeter technology that offers unmatched versatility and precision in measuring voltage, current, resistance, and capacitance
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Hardware Overview
How does it work?
Multimeter Click is managed by several different ICs, including operational amplifiers, NE555 timer, BCD decoder, frequency to voltage converter, and finally an A/D converter (ADC). The auxiliary ICs for providing -5V and the ADC referent voltage of 2.048V, are also present. The Click board™ uses the MCP3204, a four-channel, 12-bit ADC with an SPI interface, from Microchip. The conditioned signals are routed to each input of the ADC. The input channel is selected by the initial SPI command, after the #CS (chip select) pin becomes LOW. Three configuration LSBs are used to set the sampling channel (D0-D2), while the fourth bit (D3) sets the mode. The ADC is routed to work with single-ended inputs, and therefore this bit should always be set as 1. A differential input amplifier is used to amplify the voltage difference across the shunt resistor. One half of the MCP607, a dual CMOS op-amp from Microchip is used for that purpose. The value of the shunt resistor is 0.1Ω, which allows up to 1A of current to be measured. Since the ammeter is connected in series, the shunt resistor has to be of a very small value, in order to prevent interferences with the measuring circuitry. This is one of the basic requirements of the ammeter. The voltage drop at the shunt is amplified by the differential op-amp (by the factor of 10), and the op-amp output is routed to one of the ADC inputs, which is labeled I on the schematic. The op-amp uses half of the referent voltage (Vref) as the virtual GND so that both positive and negative values can be converted. When measuring a voltage, the internal
resistance of the voltmeter has to be large, since it is connected in parallel with the component across which the voltage is measured. The Click board™ uses the MCP609, a quad CMOS op-amp, configured as dual-buffer and a differential amplifier. It is the same device as the MCP607, but with four integrated op-amps. Two integrated op-amps work as buffers with voltage dividers at their non-inverting inputs, while the third op-amp acts as the actual differential amplifier. Again, the op-amp uses the virtual GND, set at half of the Vref for the output biasing. This allows both negative and positive voltage potential to be measured, across the load connected at the input terminal. The output from the differential amplifier is routed to the ADC input labeled as U. Measurement of the resistance consists of a voltage divider, which is formed by an unknown resistance connected to the resistance measuring terminal, and a selectable, known, reference value resistor. The voltage applied to the voltage divider is also known (Vref). The middle tap of the divider is routed directly to the ADC input pin labeled as R, allowing reading of the voltage which directly depends on the unknown resistance. The CD4028B, a BCD decoder IC from Texas Instruments is used to select the correct reference resistance range. Three input pins (A, B, C) of the CD4028B are used to activate one of 6 MOSFET gates, via the logic states of the AN, PWM and INT pins of the mikroBUS™, which connect the desired reference resistor to the measuring circuit. The capacitance property can be measured with
many multimeters commercially available, but it is not something included in some cheaper models. It consists of the NE555 precision timer, configured as an astable multivibrator. It generates impulses, set to about 50% duty cycle, with the frequency of 585Hz. This signal is converted by the LM2907MX, a frequency to voltage converter from Texas Instruments. The unknown capacitance is connected to the threshold input of the NE555, affecting the frequency of the pulses. The LM2907MX responds by changing the output voltage, fed to a differential op-amp. The higher the connected capacitance, the lower the LM2907 output becomes. The DC signal is then passed through another differential amplifier and routed to the ADC input labeled as CU, so it can be sampled by the ADC and read via the SPI. A software (or a firmware) running on the host MCU is required, in order to transform raw ADC readings and show them on an output device. The library provided with the Multimeter click offers a set of functions, which output straight-forward measurements and can be implemented easily in a custom code. Before actual measurement, as a part of the device initialization procedure, a calibration routine needs to be performed, so that components tolerances are taken into an account. Therefore, there should be nothing connected at the input terminals of the Multimeter click, until it is initialized by the software. The provided example application demonstrates how to use this click board, so it can be used as a starting point for future development.
Features overview
Development board
Nucleo-64 with STM32F446RE 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-M4
MCU Memory (KB)
512
Silicon Vendor
STMicroelectronics
Pin count
64
RAM (Bytes)
131072
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
Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the Nucleo 64 with STM32F446RE MCU as your development board.
Track your results in real time
Application Output via Debug Mode
1. Once the code example is loaded, pressing the "DEBUG" button initiates the build process, programs it on the created setup, and enters Debug mode.
2. After the programming is completed, a header with buttons for various actions within the IDE becomes visible. Clicking the green "PLAY" button starts reading the results achieved with the Click board™. The achieved results are displayed in the Application Output tab.
Software Support
Library Description
This library contains API for Multimeter Click driver.
Key functions:
multimeter_read_resistance- This function reads and returns resistance datamultimeter_read_voltage- This function reads and returns voltage datamultimeter_read_voltage- This function reads and returns current data.
Open Source
Code example
This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.
/*!
* \file
* \brief Multimeter Click example
*
* # Description
* This example showcases how to configure, initialize and use the Multimeter click. The
* click measures resistance in Ohms, voltage in mVs, current in mAs and capacitance in nFs
* using a dual CMOS and quad CMOS op-amps, an ADC and other on board modules.
*
* The demo application is composed of two sections :
*
* ## Application Init
* This function initializes and configures the logger and click modules. Additional
* calibration of the measurement components is done in the default_cfg(...) function.
*
* ## Application Task
* This function measures and displays resistance, voltage, current and capacitance data.
* It does so every second.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "multimeter.h"
// ------------------------------------------------------------------ VARIABLES
static multimeter_t multimeter;
static log_t logger;
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( )
{
log_cfg_t log_cfg;
multimeter_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.
multimeter_cfg_setup( &cfg );
MULTIMETER_MAP_MIKROBUS( cfg, MIKROBUS_1 );
multimeter_init( &multimeter, &cfg );
multimeter_default_cfg( &multimeter );
}
void application_task ( )
{
float resistance;
float voltage;
float current;
float capacitance;
resistance = multimeter_read_resistance( &multimeter );
log_printf( &logger, " * Resistance: %.3f Ohms * \r\n", resistance );
voltage = multimeter_read_voltage( &multimeter );
log_printf( &logger, " * Voltage: %.3f mV * \r\n", voltage );
current = multimeter_read_current( &multimeter );
log_printf( &logger, " * Current: %.3f mA * \r\n", current );
capacitance = multimeter_read_capacitance( &multimeter );
log_printf( &logger, " * Capacitance: %.3f nF * \r\n", capacitance );
log_printf( &logger, "------------------------\r\n" );
Delay_1sec( );
}
void main ( )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
