Beginner
10 min

Control resistance using digital signals with MCP4161 and PIC18F46K20

8-bit single SPI digital potentiometer with non-volatile memory

DIGI POT Click with Curiosity HPC

Published Nov 01, 2023

Click board™

DIGI POT Click

Development board

Curiosity HPC

Compiler

NECTO Studio

MCU

PIC18F46K20

Achieve digital control of electrical parameters through this cutting-edge digital potentiometer solution, simplifying system tuning and optimization

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Hardware Overview

How does it work?

DIGI POT Click is based on the MCP4161, an 8-bit single SPI digital POT with non-volatile memory from Microchip. The MCP4161 has a resistance of 10kΩ and low wiper resistance, with a typical 75Ω. It can be used as a three-terminal potentiometer or a two-terminal rheostat while floating either of the terminals (A or B). DIGI POT Click has four screw terminals: PA and PB as analog terminals A and B of the MCP4161, a PW as a wiper terminal of the digital potentiometer, and one for ground. The PA and PB terminals do not have polarity restrictions; PA can be a higher voltage than PB and vice-versa.

The position of the wiper (PB) terminal is controlled by the value in the 8-bit wiper resistance register. There are two functional modes of this Click board™. When all three terminals are used, the MCP4161 generates a voltage divider, where the voltage divider at wiper-to-PA and wiper-to-PB is proportional to the input voltage at PA to PB. It operates in rheostat mode as a variable resistor when only two terminals are used. DIGI POT Click communicates with the host MCU using the 3-Wire SPI serial interface as a write-only. The SCK timing frequency maximum is 10MHz. It features a

WiperLock™ Technology for automatically recalling saved wiper settings from EEPROM. In addition to the SMD MCP4161, this Click board™ features 6 PTHs for the DIP variant of this chip. 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.

DIGI POT Click hardware overview image

Features overview

Development board

Curiosity HPC, standing for Curiosity High Pin Count (HPC) development board, supports 28- and 40-pin 8-bit PIC MCUs specially designed by Microchip for the needs of rapid development of embedded applications. This board has two unique PDIP sockets, surrounded by dual-row expansion headers, allowing connectivity to all pins on the populated PIC MCUs. It also contains a powerful onboard PICkit™ (PKOB), eliminating the need for an external programming/debugging tool, two mikroBUS™ sockets for Click board™ connectivity, a USB connector, a set of indicator LEDs, push button switches and a variable potentiometer. All

these features allow you to combine the strength of Microchip and Mikroe and create custom electronic solutions more efficiently than ever. Each part of the Curiosity HPC development board contains the components necessary for the most efficient operation of the same board. An integrated onboard PICkit™ (PKOB) allows low-voltage programming and in-circuit debugging for all supported devices. When used with the MPLAB® X Integrated Development Environment (IDE, version 3.0 or higher) or MPLAB® Xpress IDE, in-circuit debugging allows users to run, modify, and troubleshoot their custom software and hardware

quickly without the need for additional debugging tools. Besides, it includes a clean and regulated power supply block for the development board via the USB Micro-B connector, alongside all communication methods that mikroBUS™ itself supports. Curiosity HPC development board allows you to create a new application in just a few steps. Natively supported by Microchip software tools, it covers many aspects of prototyping thanks to many number of different Click boards™ (over a thousand boards), the number of which is growing daily.

Curiosity HPC double image

Microcontroller Overview

MCU Card / MCU

PIC18F46K20

Architecture

PIC

MCU Memory (KB)

64

Silicon Vendor

Microchip

Pin count

40

RAM (Bytes)

3936

Used MCU Pins

mikroBUS™ mapper

NC
NC
AN
NC
NC
RST
SPI Chip Select
RA3
CS
SPI Clock
RB1
SCK
NC
NC
MISO
SPI Data IN
RB3
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
NC
NC
PWM
NC
NC
INT
NC
NC
TX
NC
NC
RX
NC
NC
SCL
NC
NC
SDA
Power Supply
5V
5V
Ground
GND
GND
1

Take a closer look

Schematic

DIGI POT Click Schematic schematic

Step by step

Project assembly

Curiosity HPC front no-mcu image hardware assembly

Start by selecting your development board and Click board™. Begin with the Curiosity HPC as your development board.

Curiosity HPC front no-mcu image hardware assembly
GNSS2 Click front image hardware assembly
MCU DIP 40 hardware assembly
Prog-cut hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
Curiosity HPC Access MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
Necto image step 5 hardware assembly
Necto image step 6 hardware assembly
Necto DIP image step 7 hardware assembly
Necto No Display image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Debug Image Necto Step hardware assembly

Track your results in real time

Application Output

After loading the code example, pressing the "DEBUG" button builds and programs it on the selected setup.

Application Output Step 1

After programming is completed, a header with buttons for various actions available in the IDE appears. By clicking the green "PLAY "button, we start reading the results achieved with Click board™.

Application Output Step 3

Upon completion of programming, the Application Output tab is automatically opened, where the achieved result can be read. In case of an inability to perform the Debug function, check if a proper connection between the MCU used by the setup and the CODEGRIP programmer has been established. A detailed explanation of the CODEGRIP-board connection can be found in the CODEGRIP User Manual. Please find it in the RESOURCES section.

Application Output Step 4

Software Support

Library Description

This library contains API for DIGI POT Click driver.

Key functions:

  • digipot_set_wiper_positions - This function sets 8-bit wiper positions data

  • digipot_convert_output - This function convert 10-bit ADC value to volatage reference

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 main.c
 * @brief DigiPot Click example
 *
 * # Description
 * The demo application changes the resistance using DIGIPOT Click.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes SPI and LOG modules.
 *
 * ## Application Task
 * This is an example which demonstrates the use of DIGI POT Click board.
 * Increments the wiper position by 10 positions every 5 seconds.
 *
 * @author Stefan Ilic
 *
 */

#include "board.h"
#include "log.h"
#include "digipot.h"

static digipot_t digipot;
static log_t logger;

uint8_t wiper_pos;

void application_init ( void ) {
    log_cfg_t log_cfg;  /**< Logger config object. */
    digipot_cfg_t digipot_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.

    digipot_cfg_setup( &digipot_cfg );
    DIGIPOT_MAP_MIKROBUS( digipot_cfg, MIKROBUS_1 );
    err_t init_flag  = digipot_init( &digipot, &digipot_cfg );
    if ( SPI_MASTER_ERROR == init_flag ) {
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );
    }

    log_printf( &logger, "----------------\r\n" );
    log_printf( &logger, " DIGI POT Click\r\n" );
    log_printf( &logger, "----------------\r\n" );
}

void application_task ( void ) {
    for ( uint16_t n_cnt = 127; n_cnt < 255; n_cnt += 10 ) {
        wiper_pos = ( uint8_t ) n_cnt;
        digipot_set_wiper_positions( &digipot, wiper_pos );
        Delay_ms( 5000 );
    }
}

void main ( void ) {
    application_init( );

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

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

Additional Support

Resources