Accurately quantify applied forces with FSR and PIC18F2585 for enhanced analysis

Unveiling force measurement like never before!

Published Nov 01, 2023

Click board™

Force Click

Dev Board

EasyPIC v8

Compiler

NECTO Studio

MCU

PIC18F2585

Harness the power of precise force measurement to enhance quality control across various applications

Hardware Overview

How does it work?

Force Click is based on the circuitry that allows the implementation of Force Sensing Resistors from Interlink Electronics. The Force Sensing Resistor is a thin sensor made of two membranes separated by a spacer around the edges. When pressed, the gap between the two membranes gets closed. This shorts the two membranes together with a resistance proportional to the applied force. This force sensitivity is optimized for human-machine interface devices, including automotive electronics, medical systems, industrial controls, and robotics. The FSR is a robust sensor with up to 10M of actuation and features a low device rise time of under 3 microseconds, as well as continuous analog force resolution. Force Click

sends analog values to the host MCU over the AN pin of the mikroBUS™ socket by using an OPA344, a low-power, single supply, rail-to-rail operational amplifier from Texas Instruments. This unity-gain stable OPAMP is ideal for driving sampling analog to digital converters. Rail-to-rail input and output swing significantly increase dynamic range, especially in low-power supply applications. The input to this OPA344NA is driven directly from the screw terminal and the force-sensing resistor. An ADM8829, a switched-capacitor voltage inverter with shutdown from Analog Devices, feeds the other side of the screw terminal and the force-sensing resistor. This charge-pump voltage inverter generates a negative power supply

from a positive input. The voltage conversion task is achieved using a switched capacitor technique using two external charge storage capacitors. An on-chip oscillator and switching network transfers charge between the charge storage capacitors. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the PWR 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

EasyPIC v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports many high pin count 8-bit PIC microcontrollers from Microchip, regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, EasyPIC v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the EasyPIC v8 development board contains the components necessary for the most efficient operation of the same board. In addition to the advanced integrated CODEGRIP programmer/debugger module, which offers many valuable programming/debugging options and seamless integration with the Mikroe software environment, the board also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector.

Communication options such as USB-UART, USB DEVICE, and CAN are also included, including the well-established mikroBUS™ standard, two display options (graphical and character-based LCD), and several different DIP sockets. These sockets cover a wide range of 8-bit PIC MCUs, from the smallest PIC MCU devices with only eight up to forty pins. EasyPIC v8 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.

Microcontroller Overview

MCU Card / MCU

Architecture

PIC

MCU Memory (KB)

Silicon Vendor

Microchip

Pin count

RAM (Bytes)

3328

Used MCU Pins

mikroBUS™ mapper

Analog Output

RA3

RST

SCK

MISO

MOSI

Power Supply

3.3V

Ground

GND

PWM

INT

SCL

SDA

Power Supply

Ground

GND

Take a closer look

Schematic

Step by step

Project assembly

EasyPIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the EasyPIC v8 as your development board.

NECTO Output Selection Step Image hardware assembly

In the advanced settings, pay special attention to the Redirect standard output field. By default, it is set to Application output as the method of displaying final results. To show results via a UART terminal, select the “UART” option in that field and click the “SAVE” button. You will be returned to the Compiler field, and now you can move on to the next step by pressing the “NEXT” button.

Rotary B 2 Click front image hardware assembly

EasyPIC v8 28pin-DIP - upright/background hardware assembly

NECTO Compiler Selection Step Image hardware assembly

Necto DIP image step 7 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.

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.

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".

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.

Software Support

Library Description

This library contains API for Force Click driver.

Key functions:

force_generic_read - This function reads ADC data
force_get_resistance - This function calculates resistance data based on the ADC input
force_get_correction_factor - This function calculates the correction factor based on temperature and humidity 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 Force Click example
 * 
 * # Description
 * This example showcases how to initialize and configure the logger and click modules and 
 * read and display ADC voltage data read from the analog pin.
 *
 * The demo application is composed of two sections :
 * 
 * ## Application Init 
 * This function initializes and configures the logger and click modules.
 * 
 * ## Application Task  
 * This function reads and displays ADC voltage data from the analog pin every second. 
 * 
 * \author MikroE Team
 *
 */
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "force.h"

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

static force_t force;
static log_t logger;

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

void application_init ( )
{
    log_cfg_t log_cfg;
    force_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 ----" );

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

    //  Click initialization.

    force_cfg_setup( &cfg );
    FORCE_MAP_MIKROBUS( cfg, MIKROBUS_1 );
    force_init( &force, &cfg );
}

void application_task ( )
{
    force_data_t tmp;
    
    //  Task implementation.
    
    tmp = force_generic_read ( &force );
    log_printf( &logger, " * ADC value : %d \r\n", tmp );
    log_printf( &logger, "--------------------- \r\n" );
    Delay_ms( 1000 );
}

void main ( )
{
    application_init( );

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

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