Intermediate
30 min
0

Make cutting-edge A/D conversion with LTC2500-32 and PIC18LF46K40

Seamless transition, superior accuracy

ADC 7 Click with EasyPIC v7

Published Jun 08, 2023

Click board™

ADC 7 Click

Development board

EasyPIC v7

Compiler

NECTO Studio

MCU

PIC18LF46K40

Enhance the performance of your designs with the power of our Analog-To-Digital converter

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Hardware Overview

How does it work?

ADC 7 Click is based on the LTC2500-32, a 32-bit oversampling ADC with a configurable digital filter from Analog Devices. The integrated configurable filter is used to process the data from the 32-bit successive approximation register (SAR) core, providing a very low noise on the output, with a high dynamic range of up to 148dB. It also simplifies the design, as it relaxes anti-aliasing filter requirements for the input signal. The LTC2500-32 ADC also allows external reference voltage; therefore, the Click board™ uses 4.096V from a tiny fixed reference voltage IC from Microchip, the MCP1541. There is a two-pole screw terminal on the Click board™, with its inputs routed to the +IN and -IN pins of the ADC IC. The input signal can be bipolar, unipolar, or differential, swinging from 0 to VREF. Inputs are buffered with two LTC2057 operational amplifiers. These low-noise op-amps adjust the input impedance, as the LTC2500-32 ADC performs optimally when driven with low-impedance sources. The inputs are DC coupled - no decoupling capacitors are used on the input signal path. The LTC2500-32 has two SDO pins available (dual SPI interface), yet only SDOA pin is used on this Click board™, offering conversion data from the programmable digital filter. The RDLA pin should be set to a LOW logic level to initiate the SPI communication. It is routed to the CS pin of the mikroBUS™, while the SDOA pin is routed to the MISO pin of the mikroBUS™, labeled as SDO. Configured like this, it is possible to use the standard

four-pin SPI interface of the mikroBUS™ to communicate with the Click board™. The digital filter can be programmed via the SPI interface (SDI pin of the mikroBUS™), or it can use the PRE pin of the ADC IC. When the PRE pin is set to a HIGH logic level, a logic state on the SDI pin will be used to select one of two filters presets. Otherwise, the filter can be configured via the SPI interface when the PRE pin is set to a LOW logic level. PRE pin is routed to the RST pin of the mikroBUS™ and labeled as PRE. This IC uses an external signal to initiate the conversion process. The internal conversion process starts when a rising edge appears on the MCLK pin. For optimal performance, the manufacturer recommends that the external signal pulse duration should be 40nS. The MCLK pin is routed to the PWM pin of the mikroBUS™ and is labeled as MCK. After a rising edge on the MCLK pin, the ADC starts sampling by comparing the input voltage with the binary-weighted fractions of the reference voltage. The sampled input is then passed through the successive approximation algorithm (SAR ADC type). The conversion data comprises 24 bits for the differential voltage, 7 bits for the common mode voltage, and one flag bit used as a signal overflow indicator (VIN > VREF). This data is then passed to the filter section, which stores a 32-bit processed value on the output register. The ADC IC compares the differential input voltage with the 2 × VREF, divided into 232 levels, resulting in a 1.9mV resolution (using 4.096V as a reference).

The wide common-mode input range (from 0V up to VREF), coupled with the high common-mode rejection rate, allows all types of signals to be sampled by the device: pseudo-differential unipolar, pseudo-differential bipolar, and fully differential. It is a unique feature of the LTC2500-32 ADC device. During the conversion phase, the BUSY pin is kept at the HIGH logic level (Hi-Z). This pin is driven to a LOW logic level when the conversion ends. The BUSY pin indicates the conversion-in-progress state and is routed to the mikroBUS™ INT pin, labeled as BSY. Another pin of the LTC2500-32 ADC with a similar function indicates that data is ready to be read at the output register. This pin is labeled as DRL and routed to the mikroBUS™ AN pin. By using these pins as the interrupt sources, the host MCU can achieve optimized data acquisition timing, not having to poll the ADC until it gets ready. The Click board™ uses both 3.3V and 5V rails of the mikroBUS™.The 3.3V rail provides the operating voltage for the ADC IC, which is 2.5V. Therefore, a small LDO is used to obtain this voltage. The 5V rail of the mikroBUS™ is used as the input voltage for the MCP1541 reference voltage source. Since the logic section of the LTC2500-32 ADC can operate with voltages from 1.8V up to 5V, no additional communication level shifting ICs are required, and the Click board™ can operate with both 3.3V and 5V MCUs. 

ADC 7 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

PIC18LF46K40

Architecture

PIC

MCU Memory (KB)

64

Silicon Vendor

Microchip

Pin count

40

RAM (Bytes)

3728

Used MCU Pins

mikroBUS™ mapper

Data Ready Indicator
RA2
AN
Filter Preset Enable
RE1
RST
SPI Chip Select
RE0
CS
SPI Clock
RC3
SCK
SPI Data OUT
RC4
MISO
SPI Data IN
RC5
MOSI
Power supply
3.3V
3.3V
Ground
GND
GND
Sampling Trigger
RC0
PWM
Busy Indicator
RB0
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

ADC 7 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
GNSS2 Click front image hardware assembly
MCU DIP 40 hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
EasyPIC v7 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 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 ADC 7 Click driver.

Key functions:

  • adc7_set_config Function performs the device configuration by sending configuration data

  • adc7_start_conv_cycle Function generates clock signal on MCK pin and on that way starts conversion

  • adc7_read_results Function reads voltage value from AD converter and calculates this value to mV

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 ADC7 Click example
 * 
 * # Description
 * This application collects data from the analog signal, calculates and logs the
 * converted voltage value.
 *
 * The demo application is composed of two sections :
 * 
 * ## Application Init 
 * Initializes driver and performs configuration for conversion cycles.
 * 
 * ## Application Task  
 * Performs the determined number of conversion cycles which are necessary for averaging. 
 * When all conversion cycles are done, it reads the converted voltage value.
 * Results will be logged on UART terminal every second.
 * 
 * \author MikroE Team
 *
 */
// ------------------------------------------------------------------- INCLUDES

#include "board.h"
#include "log.h"
#include "adc7.h"

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

static adc7_t adc7;
static log_t logger;

static float voltage_data;

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

void application_init ( void )
{
    log_cfg_t log_cfg;
    adc7_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 ----" );
    Delay_ms( 100 );

    //  Click initialization.

    adc7_cfg_setup( &cfg );
    ADC7_MAP_MIKROBUS( cfg, MIKROBUS_1 );
    adc7_init( &adc7, &cfg );
    
    adc7_default_cfg( &adc7 );
}

void application_task ( void )
{
    adc7_start_conv_cycle( &adc7 );
    adc7_read_results( &adc7, &voltage_data );
    log_printf( &logger, "Voltage: %.2f mV\r\n", voltage_data );

    Delay_ms( 1000 );
}

void main ( void )
{
    application_init( );

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

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

Additional Support

Resources