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Embrace the future of stretch force measurement using PIC18LF2455

From flex to facts

Stretch Click with EasyPIC v7

Published Nov 01, 2023

Click board™

Stretch Click

Development board

EasyPIC v7

Compiler

NECTO Studio

MCU

PIC18LF2455

Revolutionize applications across industries by harnessing conductive rubber cords to accurately measure and optimize stretch forces for enhanced design and performance

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Hardware Overview

How does it work?

Stretch Click is based on the circuitry that allows measuring the stretch forces of the 2mm diameter conductive rubber cord. In a "relaxed" state, the resistance is about 130 ohms per centimeter. The resistance increases as you stretch it out (the particles get further apart); for example, a 15cm piece is proportional to 2.1k ohms (25cm long stretch is 26/15*2.1K = 3.5k ohms). You can stretch the rubber about 50-70% longer than the resting length, so a 15cm piece shouldn't be stretched more than 25cm. Once the force is released, the rubber will shrink back, although it's not very

"fast" and it takes a minute or two to revert to its original length. The resistance of the cord increases when stretched, impacting the reverse voltage on the voltage divider, which can be measured. The Stretch Click allows stretch force readings to be available on an analog AN pin of the mikroBUS™ socket. It's not a true linear sensor, and the resistance may vary from batch to batch, so we consider it a way to measure stretching motion, but it isn't really precise. In addition, this Click board™ features a user-configurable LED1 light-emitting diode that can

visually represent the measured force. This LED1 can be controlled over the PWM pin of the mikroBUS™ socket. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the J1 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.

Stretch Click hardware overview image

Features overview

Development board

EasyPIC v7 is the seventh generation of PIC development boards specially designed to develop embedded applications rapidly. It supports a wide range of 8-bit PIC microcontrollers from Microchip and has a broad set of unique functions, such as a powerful onboard mikroProg programmer and In-Circuit debugger over USB-B. The development board is well organized and designed so that the end-user has all the necessary elements in one place, such as switches, buttons, indicators, connectors, and others. With four different connectors for each port, EasyPIC v7 allows you to connect accessory boards, sensors, and custom electronics more efficiently than ever. Each part of

the EasyPIC v7 development board contains the components necessary for the most efficient operation of the same board. An integrated mikroProg, a fast USB 2.0 programmer with mikroICD hardware In-Circuit Debugger, offers many valuable programming/debugging options and seamless integration with the Mikroe software environment. Besides it also includes a clean and regulated power supply block for the development board. It can use various external power sources, including an external 12V power supply, 7-23V AC or 9-32V DC via DC connector/screw terminals, and a power source via the USB Type-B (USB-B) connector. Communication options such as

USB-UART and RS-232 are also included, alongside the well-established mikroBUS™ standard, three display options (7-segment, graphical, and character-based LCD), and several different DIP sockets. These sockets cover a wide range of 8-bit PIC MCUs, from PIC10F, PIC12F, PIC16F, PIC16Enh, PIC18F, PIC18FJ, and PIC18FK families. EasyPIC v7 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

EasyPIC v7 horizontal image

Microcontroller Overview

MCU Card / MCU

default

Architecture

PIC

MCU Memory (KB)

24

Silicon Vendor

Microchip

Pin count

28

RAM (Bytes)

2048

Used MCU Pins

mikroBUS™ mapper

Analog Output
RA3
AN
NC
NC
RST
SPI Chip Select
RA5
CS
SPI Clock
RC3
SCK
SPI Data OUT
RC4
MISO
SPI Data IN
RC5
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
External Sync
RC1
PWM
Interrupt
RB1
INT
NC
NC
TX
NC
NC
RX
NC
NC
SCL
NC
NC
SDA
NC
NC
5V
Ground
GND
GND
2

Take a closer look

Schematic

Stretch Click Schematic schematic

Step by step

Project assembly

EasyPIC v7 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the EasyPIC v7 as your development board.

EasyPIC v7 front image hardware assembly
LTE IoT 5 Click front image hardware assembly
MCU DIP 28 hardware assembly
LTE IoT 5 Click complete accessories setup image hardware assembly
EasyPIC v7 Access MB 2 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto DIP image step 7 hardware assembly
EasyPIC PRO v7a Display Selection Necto Step hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for Stretch Click driver.

Key functions:

  • stretch_cfg_setup - Config Object Initialization function

  • stretch_turn_on_led - Turn on the LED function

  • stretch_turn_off_led -Turn off the LED function

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 Stretch Click example
 * 
 * # Description
 * The application is for stretch measuring 
 *
 * The demo application is composed of two sections :
 * 
 * ## Application Init 
 * Initialization driver enables GPIO and ADC, turn off the LED and starts write log. 
 * 
 * ## Application Task  
 * This is a example which demonstrates the use of Stretch Click board. Stretch Click reads and display ADC value.
 * 
 * \author MikroE Team
 *
 */
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "stretch.h"

// ------------------------------------------------------------------ VARIABLES

static stretch_t stretch;
static log_t logger;

// ------------------------------------------------------- ADDITIONAL FUNCTIONS


// ------------------------------------------------------ APPLICATION FUNCTIONS

void application_init ( void )
{
    log_cfg_t log_cfg;
    stretch_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.

    stretch_cfg_setup( &cfg );
    STRETCH_MAP_MIKROBUS( cfg, MIKROBUS_1 );
    stretch_init( &stretch, &cfg );

    Delay_100ms();

    log_printf( &logger, "------------------- \r\n" );
    log_printf( &logger, "  Stretch  click  "  );
    log_printf( &logger, "-------------------\r\n" );

    stretch_turn_off_led( &stretch );
    Delay_100ms( );

    log_printf( &logger, " ADC Initializated " );
    log_printf( &logger, "-------------------" );
}

void application_task ( void )
{
    stretch_data_t tmp;
    
    //  Task implementation.
    
    tmp = stretch_generic_read ( &stretch );
    log_printf( &logger, "** ADC value : [DEC]- %d, [HEX]- 0x%x \r\n", tmp, tmp );
    Delay_ms( 1000 );

    Delay_100ms( );
    
    if ( tmp < 500 )
    {
        stretch_turn_on_led( &stretch );
    }
        
    else
    {
        stretch_turn_off_led( &stretch );
    }

    log_printf( &logger, " Resistance : %d \r\n", tmp );
    log_printf( &logger, "-------------------\r\n" );
    Delay_1sec( );
}

void main ( void )
{
    application_init( );

    for ( ; ; )
    {
        application_task( );
    }
}


// ------------------------------------------------------------------------ END

Additional Support

Resources