Monitor pH in various samples for diagnostic insights with MCP607 and STM32F091RC
Decode the secrets of acidity and alkalinity
Published Feb 26, 2024
Click board™
pH 2 Click
Dev. board
Nucleo-64 with STM32F091RC MCU
Compiler
NECTO Studio
MCU
STM32F091RC
With a solution like this one designed to determine the acidity or alkalinity of a sample, measured using the pH electrode, you can embark on various applications and activities across different industries and fields
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Hardware Overview
How does it work?
pH 2 Click is based on the MCP607, a low-bias current operational amplifier from Microchip. This Click board™ operation is based on measuring hydrogen ion activity and produces an electrical potential or voltage. An electric potential develops when two liquids of different pH come into contact at opposite sides of a pH electrode thin glass membrane. The pH electrode represents a passive sensor, which means no excitation source (voltage or current) is required. It is classified as a bipolar sensor because its output can swing above and below the reference point. This board is a perfect solution for a wide variety of pH-sensing applications, including water treatment, chemical processing, medical instrumentation, and environmental test systems. pH 2 Click is used to detect the concentration of hydrogen ions in a solution and convert it into a corresponding
usable output signal. Because the pH electrode produces a bipolar signal, the electrode signal is first level shifted by the MCP607, a low bias current Op Amp set up in a unity-gain configuration with configurable reference for its calibration. Second, due to the high impedance of the electrode, another Op Amp inside the MCP607 provides the required high-input impedance buffer. A buffered signal can be then converted to a digital value using the MCP3221, a successive approximation A/D converter with a 12-bit resolution from Microchip using a 2-wire I2C compatible interface, or can be sent directly to an analog pin of the mikroBUS™ socket labeled as AN. The selection can be performed using an onboard SMD switch labeled OUT SEL, placing it in an appropriate position marked as AN or ADC. It is important to note that a pH electrode's sensitivity varies over
temperature. For this reason, it is possible to add the DS18B20, 1-wire thermometer via the DQ terminal to the pH 2 Click, whose temperature can be monitored via the DQ pin on the mikroBUS™ socket. In addition, the user can digitally monitor different statuses in operation through the ST1 and ST2 pins on the mikroBUS™ socket or through visual detection on the STAT1 and STAT2 LEDs. 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-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.
This probe can be used with all pH meters with an input for the BNC connection with a 1m cable. The sensitive part of the probe (in the shape of a ball) is partially protected by a probe's plastic body, which reduces the possibility of mechanical damage. The EPH101 is used to measure the pH value of various liquids (due to the present plastic protection), and it can also be immersed in liquids inflowed in a system). It is stored in a plastic gel bottle with a very long shelf life. A pH (potential of Hydrogen) probe measures the hydrogen ion activity in a liquid. A membrane at the tip of a pH probe permits hydrogen ions from the liquid to be measured to defuse into the outer layer of the membrane while larger ions remain in the solution. The difference in the concentration of hydrogen ions outside the probe vs. inside the pH probe creates a small current proportional to the concentration of hydrogen ions in the measured liquid.
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 pH 2 Click driver.
Key functions:
ph2_calibrate- Ph 2 calibrate functionph2_calculate_ph- Ph 2 calculate pH value functionph2_calibrate_offset- Ph 2 calibrate offset 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 main.c
* @brief pH 2 Click Example.
*
* # Description
* This library contains API for pH 2 Click driver.
* The library initializes and defines the I2C bus drivers or
* ADC drivers to read data from pH probe.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes the driver and performs offset calibration,
* as well as calibration in pH-neutral substance.
*
* ## Application Task
* This example demonstrates the use of the pH 2 Click board by
* reading pH value of the substance where probe is placed.
*
* @author Stefan Ilic
*
*/
#include "board.h"
#include "log.h"
#include "ph2.h"
static ph2_t ph2; /**< pH 2 Click driver object. */
static log_t logger; /**< Logger object. */
void application_init ( void )
{
log_cfg_t log_cfg; /**< Logger config object. */
ph2_cfg_t ph2_cfg; /**< Click config object. */
/**
* 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.
ph2_cfg_setup( &ph2_cfg );
PH2_MAP_MIKROBUS( ph2_cfg, MIKROBUS_1 );
err_t init_flag = ph2_init( &ph2, &ph2_cfg );
if ( ( ADC_ERROR == init_flag ) || ( I2C_MASTER_ERROR == init_flag ) )
{
log_error( &logger, " Communication init." );
for ( ; ; );
}
log_printf( &logger, " ================================ \r\n" );
log_printf( &logger, " Performing calibration \r\n" );
log_printf( &logger, " ================================ \r\n" );
log_printf( &logger, " Disconect BNC connector, \r\n" );
log_printf( &logger, " short-circuit it, \r\n" );
log_printf( &logger, " adjust offset potentiometer \r\n" );
log_printf( &logger, " ================================ \r\n" );
log_printf( &logger, " STAT1 - turn clockwise \r\n" );
log_printf( &logger, " STAT2 - turn counter-clockwise \r\n" );
log_printf( &logger, " ================================ \r\n" );
ph2_calibrate_offset( &ph2 );
log_printf( &logger, " Calibration completed \r\n" );
log_printf( &logger, " ================================ \r\n" );
log_printf( &logger, " Connect probe back \r\n" );
log_printf( &logger, " ================================ \r\n" );
Delay_ms( 5000 );
log_printf( &logger, " Place probe into pH \r\n" );
log_printf( &logger, " neutral substance for \r\n" );
log_printf( &logger, " mid point calibration \r\n" );
log_printf( &logger, " ================================ \r\n" );
Delay_ms( 5000 );
log_printf( &logger, " Starting calibration \r\n" );
log_printf( &logger, " ================================ \r\n" );
ph2_calibrate( &ph2, 7 );
log_printf( &logger, " Calibration done! \r\n" );
log_printf( &logger, " ================================ \r\n" );
log_info( &logger, " Application Task " );
log_printf( &logger, " ================================ \r\n" );
}
void application_task ( void )
{
float pH_val = 0;
ph2_calculate_ph( &ph2, &pH_val );
log_printf( &logger, " pH value: %.3f \r\n", pH_val );
log_printf( &logger, " ================================ \r\n" );
Delay_ms( 1000 );
}
void main ( void )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
