Achieve precise and reliable measurements of resistor values using AD8616 and PIC32MZ2048EFM100

Ohm's law made easy: Explore the power of our resistor value detector

R Meter Click with Curiosity PIC32 MZ EF

Published Sep 28, 2023

Click board™

R Meter Click

Dev Board

Curiosity PIC32 MZ EF

Compiler

NECTO Studio

MCU

PIC32MZ2048EFM100

Experience a new era of accuracy with our resistor measurement solution, designed to provide real-time data on resistor values for a wide range of applications

Hardware Overview

How does it work?

R Meter Click is based on the AD8616, a precision 20MHz CMOS rail-to-rail input/output operational amplifier from Analog Devices. This dual-channel amplifier features low offset voltage, wide signal bandwidth, and low input voltage and current noise. The analog output is fed to the MCP3201, a 12-bit AD converter with the SPI serial interface from Microchip. The MCP3201 provides a single pseudo-differential input, features on-chip sample and hold, a maximum sampling rate of up to 100ksps, and more. The MCP3201 gets the reference voltage from the MAX6106, a low-cost, micropower, low-dropout, high-output-current voltage reference from Analog Devices. Since the AD converter has a limited min-max range

of 0-2043, the R Meter Click employs the 74HC4053, a triple 2-channel analog multiplexer/demultiplexer from Nexperia. The multiplexer adjusts the input signal to the amplifier and thus allows the same ADC to measure different scopes of values (0-1K, 1K-100K, 100K-1M). The R Meter Click is a handy tool, but it’s not to be used as a precision instrument. The linearity of the OpAmp impacts the measurement. The R Meter Click uses the 3-Wire SPI serial interface of the MCP3201 to communicate with the host MCU, with a frequency of up to 1.6MHz and supporting SPI 0 and SPI 1 modes. The voltage amplified through the AD8616 can be directly monitored through the AN pin of the mikroBUS™

socket. The supplied firmware (available on Libstock) automatically scans the ADC value and switches the multiplexer output based on the resistor place. The multiplexer interfaces directly with the host MCU through the mikroBUS™ socket over S1, S2, and S3 pins. This Click board™ can be operated only with a 5V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. Also, it 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

Curiosity PIC32 MZ EF development board is a fully integrated 32-bit development platform featuring the high-performance PIC32MZ EF Series (PIC32MZ2048EFM) that has a 2MB Flash, 512KB RAM, integrated FPU, Crypto accelerator, and excellent connectivity options. It includes an integrated programmer and debugger, requiring no additional hardware. Users can expand

functionality through MIKROE mikroBUS™ Click™ adapter boards, add Ethernet connectivity with the Microchip PHY daughter board, add WiFi connectivity capability using the Microchip expansions boards, and add audio input and output capability with Microchip audio daughter boards. These boards are fully integrated into PIC32’s powerful software framework, MPLAB Harmony,

which provides a flexible and modular interface to application development a rich set of inter-operable software stacks (TCP-IP, USB), and easy-to-use features. The Curiosity PIC32 MZ EF development board offers expansion capabilities making it an excellent choice for a rapid prototyping board in Connectivity, IOT, and general-purpose applications.

Microcontroller Overview

MCU Card / MCU

Architecture

PIC32

MCU Memory (KB)

2048

Silicon Vendor

Microchip

Pin count

100

RAM (Bytes)

524288

Used MCU Pins

mikroBUS™ mapper

Analog Output

RPB4

Select Input 3

RA9

RST

SPI Chip Select

RPD4

SPI Clock

RPD1

SCK

SPI Data OUT

RPD14

MISO

MOSI

3.3V

Ground

GND

Select Input 1

RPE8

PWM

Select Input 2

RF13

INT

SCL

SDA

Power Supply

Ground

GND

Take a closer look

Schematic

Step by step

Project assembly

Curiosity PIC32MZ EF front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Curiosity PIC32 MZ EF as your development board.

GNSS2 Click front image hardware assembly

GNSS2 Click complete accessories setup image hardware assembly

Curiosity PIC32 MZ EF MB 1 Access - upright/background hardware assembly

Curiosity PIC32 MZ EF MCU Step hardware assembly

Necto No Display image step 8 hardware assembly

Debug Image Necto Step hardware assembly

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 R Meter Click driver.

Key functions:

rmeter_get_ohms - Get resistance in OHMs function
rmeter_avg_volt - Get average voltage function
rmeter_calc - Calculations 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 R Meter Click example
 *
 * # Description
 * Demo app measures and displays resistance of a resistor connected 
 * to the R Meter click board.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initalizes SPI serial communication, LOG module and click driver.
 * Also sets the app callback handler.
 *
 * ## Application Task
 * This is an example that shows the capabilities of the R Meter click by 
 * measuring the target resistance.
 *
 * *note:*
 * R Meter click is a handy tool but it is not to be used as a high precision 
 * instrument! The linearity of the OP Amplifier impacts the measurement.
 * The range of resistance measurement goes from 1 ohm to 1M9 ohms.
 *
 * \author Nemanja Medakovic
 *
 */

#include "board.h"
#include "log.h"
#include "rmeter.h"

static rmeter_t rmeter;
static log_t logger;

void application_callback ( char *message )
{
    log_printf( &logger, "- %s\r\n", message );
}

void application_init ( void )
{
    log_cfg_t log_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... ----" );

    rmeter_cfg_t rmeter_cfg;

    //  Click initialization.

    rmeter_cfg_setup( &rmeter_cfg );
    RMETER_MAP_MIKROBUS( rmeter_cfg, MIKROBUS_1 );

    if ( rmeter_init( &rmeter, &rmeter_cfg ) == RMETER_INIT_ERROR )
    {
        log_info( &logger, "---- Application Init Error. ----" );
        log_info( &logger, "---- Please, run program again... ----" );

        for ( ; ; );
    }

    rmeter_set_callback_handler( &rmeter, application_callback );

    log_info( &logger, "---- Application Init Done. ----\n" );
}

void application_task ( void )
{
    uint16_t meas_value = rmeter_auto_scale_range_execution( &rmeter );

    float res_value;

    if ( rmeter_calculate_resistance( &rmeter, &res_value, meas_value ) == RMETER_OK )
    {
        log_printf( &logger, "  - Resistor value is %.1f ohms\r\n\n", res_value );
    }

    Delay_ms( 3000 );
}

void main ( void )
{
    application_init( );

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


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