Detect the press of an inductive touch button using LDC3114 and ATmega328P

Inductive sensing

Published Feb 14, 2024

Click board™

LDC Touch Click

Dev. board

Arduino UNO Rev3

Compiler

NECTO Studio

MCU

ATmega328P

Sense the presence and position of a conductive target object

Hardware Overview

How does it work?

LDC Touch Click is based on the LDC3114-Q1, a hybrid multichannel, high-resolution inductance-to-digital converter from Texas Instruments. This inductive sensing device enables touch button design for a human-machine interface (HMI) by measuring small deflections of conductive targets using a coil implemented on a printed circuit board. Button presses form micro-deflection in the conductive targets, which cause frequency shifts in the resonant sensors, and measures such frequency shifts determining when button press occurs. With adjustable sensitivity per input channel, the LDC3114-Q1 can reliably operate with a wide range of physical button structures and materials. The LDC3114-Q1 offers two main modes of operations: raw data access mode and button algorithm mode, which is controlled by register settings. The button mode can automatically correct any deformation in the conductive targets and offers well-matched channels allowing for differential and ratiometric measurements, which enable compensation of environmental and aging conditions

such as temperature and mechanical drift. On the other hand, it also implements a raw data access mode, where MCU can directly read the data representing the effective inductance of the sensor and implement further post-processing. This Click board™ communicates with MCU using the standard I2C 2-Wire interface to read data and configure settings, supporting a Fast Mode operation up to 400kHz. Also, the LDC3114-Q1 requires a voltage of 1.8V for its power supply to work correctly. Therefore, a small regulating LDO, the TLV700, provides a 1.8V out of 3V3 mikroBUS™ power rail. As mentioned earlier, this board contains four touch buttons, representing the only elements on the upper-top side of the board. Each button has its own LED indicator representing the activity in that field. If a touch event is detected on one of these onboard pads, the state of the corresponding LED will be changed, indicating an activated channel; more precisely, touch has been detected on that specific field. Alongside LED indicators, data from these channels can be

processed via the MCU through four pins labeled from S0 to S3, routed to the AN, RST, CS, and PWM pins of the mikroBUS™ socket, respectively. Besides, an additional interrupt signal is routed on the INT pin of the mikroBUS™ socket, indicating when a specific interrupt event occurs (touch detection, available new data, and more) alongside two power modes of operation. A Normal Power Mode for active sampling at 10, 20, 40, or 80SPS, and a Low Power Mode for reduced current consumption at 0.625, 1.25, 2.5, or 5SPS selectable through an onboard switch labeled as MODE SEL. This Click board™ can only be operated from a 3.3V logic voltage level. Therefore, the board must perform appropriate logic voltage conversion before using MCUs with different logic levels. However, the Click board™ comes equipped with a library containing functions and an example code that can be used as a reference for further development.

Features overview

Development board

Arduino UNO is a versatile microcontroller board built around the ATmega328P chip. It offers extensive connectivity options for various projects, featuring 14 digital input/output pins, six of which are PWM-capable, along with six analog inputs. Its core components include a 16MHz ceramic resonator, a USB connection, a power jack, an

ICSP header, and a reset button, providing everything necessary to power and program the board. The Uno is ready to go, whether connected to a computer via USB or powered by an AC-to-DC adapter or battery. As the first USB Arduino board, it serves as the benchmark for the Arduino platform, with "Uno" symbolizing its status as the

first in a series. This name choice, meaning "one" in Italian, commemorates the launch of Arduino Software (IDE) 1.0. Initially introduced alongside version 1.0 of the Arduino Software (IDE), the Uno has since become the foundational model for subsequent Arduino releases, embodying the platform's evolution.

Microcontroller Overview

MCU Card / MCU

Architecture

AVR

MCU Memory (KB)

Silicon Vendor

Microchip

Pin count

RAM (Bytes)

2048

You complete me!

Accessories

Click Shield for Arduino UNO has two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the Arduino UNO board without effort. The Arduino Uno, a microcontroller board based on the ATmega328P, provides an affordable and flexible way for users to try out new concepts and build prototypes with the ATmega328P microcontroller from various combinations of performance, power consumption, and features. The Arduino Uno has 14 digital input/output pins (of which six can be used as PWM outputs), six analog inputs, a 16 MHz ceramic resonator (CSTCE16M0V53-R0), a USB connection, a power jack, an ICSP header, and reset button. Most of the ATmega328P 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 Arduino UNO board with our Click Shield for Arduino UNO, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.

Used MCU Pins

mikroBUS™ mapper

Channel 0 Data

PC0

Channel 1 Data

PD2

RST

Channel 2 Data

PB2

SCK

MISO

MOSI

Power Supply

3.3V

Ground

GND

Channel 3 Data

PD6

PWM

Interrupt

PC3

INT

I2C Clock

PC5

SCL

I2C Data

PC4

SDA

Ground

GND

Take a closer look

Click board™ Schematic

Step by step

Project assembly

Click Shield for Arduino UNO front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Arduino UNO Rev3 as your development board.

Arduino UNO Rev3 front image hardware assembly

Barometer 13 Click front image hardware assembly

Arduino UNO Rev3 MB 1 - upright/background hardware assembly

Necto No Display image step 8 hardware assembly

Debug Image Necto Step hardware assembly

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 LDC Touch Click driver.

Key functions:

ldctouch_get_int_pin This function returns the INT pin logic state.
ldctouch_get_data This function reads status, out_state, and all buttons raw data.
ldctouch_set_operation_mode This function sets the operation mode.

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 LDCTouch Click example
 *
 * # Description
 * This example demonstrates the use of LDC Touch click board by configuring 
 * the buttons to trigger on finger press, and reading the buttons state in the loop.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes the driver and configures the buttons to be active on finger press.
 *
 * ## Application Task
 * Waits for the button active event interrupt and then reads and displays the buttons
 * state and their raw data on the USB UART every 200ms approximately.
 *
 * @author Stefan Filipovic
 *
 */

#include "board.h"
#include "log.h"
#include "ldctouch.h"

static ldctouch_t ldctouch;
static log_t logger;

void application_init ( void ) 
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    ldctouch_cfg_t ldctouch_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.
    ldctouch_cfg_setup( &ldctouch_cfg );
    LDCTOUCH_MAP_MIKROBUS( ldctouch_cfg, MIKROBUS_1 );
    if ( I2C_MASTER_ERROR == ldctouch_init( &ldctouch, &ldctouch_cfg ) ) 
    {
        log_error( &logger, " Communication init." );
        for ( ; ; );
    }
    
    if ( LDCTOUCH_ERROR == ldctouch_default_cfg ( &ldctouch ) )
    {
        log_error( &logger, " Default configuration." );
        for ( ; ; );
    }
    
    log_info( &logger, " Application Task " );
}

void application_task ( void ) 
{
    static bool button_active = true;
    if ( !ldctouch_get_int_pin ( &ldctouch ) )
    {
        ldctouch_data_t button_data;
        if ( LDCTOUCH_OK == ldctouch_get_data ( &ldctouch, &button_data ) )
        {
            button_active = true;
            log_printf ( &logger, " Active button: -" ); 
            for ( uint8_t cnt = 0; cnt < 4; cnt++ )
            {
                if ( button_data.out_state & ( 1 << cnt ) )
                {
                    log_printf ( &logger, " %u - ", ( uint16_t ) cnt ); 
                }
            }
            log_printf ( &logger, "\r\n Button 0 raw data: %d\r\n", button_data.ch0_raw_button );
            log_printf ( &logger, " Button 1 raw data: %d\r\n", button_data.ch1_raw_button );
            log_printf ( &logger, " Button 2 raw data: %d\r\n", button_data.ch2_raw_button );
            log_printf ( &logger, " Button 3 raw data: %d\r\n\n", button_data.ch3_raw_button );
            Delay_ms ( 200 );
        }
    }
    else
    {
        if ( button_active )
        {
            button_active = false;
            log_printf ( &logger, " Active button: - none -\r\n" ); 
        }
    }
}

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;
}

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