Intermediate
30 min

Create simple brain activity monitor with INA114 and PIC18F4685

Your brain's story, captured in every wave

EEG Click with EasyPIC v7a

Published Nov 01, 2023

Click board™

EEG Click

Dev.Board

EasyPIC v7a

Compiler

NECTO Studio

MCU

PIC18F4685

Unlock the secrets of brainwaves with our cutting-edge EEG technology

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Hardware Overview

How does it work?

EEG Click is based on the INA114, a precision instrumentation amplifier (IA) by Burr Brown®, a division of Texas Instruments specialized in high-performance analog and mixed-signal ICs. This IC offers low noise, LASER-trimmed offset voltage, and a good common-mode rejection ratio. It uses a single resistor to set up its gain, which can easily be set up to 10,000. On this Click board™, the INA114 IA has its gain set to about 12 times. Further, amplification and signal filtering is done by the MCP609, a four-channel op-amp from Microchip, so that the final gain factor is about 7800 times. Such high amplification is necessary to amplify faint voltages generated during brain activity. To fine-tune the amplification, a multi-turn precision potentiometer allows for setting the gain of the intermediate amplification stage between

10 and 100 times. Since the "brain waves " can be both positive and negative, EEG click uses a virtual GND at the potential of 2.048V. This also helps to reduce the noise from the common GND, improving the quality of the readings. The amplified brain activity signal is available at the AN pin of the mikroBUS™, allowing sampling by the host MCU. EEG measurements should be ideally conducted in an electrically isolated room since any electromagnetic interference (EMI) could corrupt the measurement data. However, the INA114 offers some EMI protection, as it features an outstanding common-mode rejection ratio (CMRR), allowing it to cancel out most of the induced interferences successfully. This Click board™ uses a 3-electrode setup, which can be connected over a 3.5mm Jack connector on the

Click board™. Although the best results can be achieved using silver-chlorine-plated electrodes, any electrode can be used. EEG uses the DRL electrode placement scheme: two electrodes are placed behind the ears, while the third is placed on the forehead. The DRL electrode (on the forehead) helps eliminate the common voltage, while two other electrodes are connected to the differential inputs of the INA114 IA. The complete signal path is very well protected against voltage spikes and transients that might appear as a result of the electrostatic discharge (ESD) in contact with the human body, so there is a set of ESD suppressing diodes and TVS diodes, which prevent sensitive IA and operational amplifiers on its output to become damaged by ESD events.

EEG Click hardware overview image

Features overview

Development board

EasyPIC v7a is the seventh generation of PIC development boards specially designed for the needs of rapid development of embedded applications. It supports a wide range of 8-bit PIC microcontrollers from Microchip and has a broad set of unique functions, such as the first-ever embedded debugger/programmer over USB-C. 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 v7a allows you to connect accessory boards, sensors, and custom electronics more efficiently than ever. Each part of the EasyPIC v7a 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 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-C (USB-C) 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 v7a 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 v7a double side image

Microcontroller Overview

MCU Card / MCU

PIC18F4685

Architecture

PIC

MCU Memory (KB)

96

Silicon Vendor

Microchip

Pin count

40

RAM (Bytes)

3328

You complete me!

Accessories

3-wire ECG/EMG cable comes with a convenient 3.5mm phone jack, and it is designed for electrocardiogram recording. This 1m cable is a practical companion for medical professionals and enthusiasts. To complement this cable, you can also use single-use adhesive ECG/EMG electrodes measuring 48x34mm, each equipped with an ECG/EMG cable stud adapter. These electrodes ensure a seamless experience when paired with our ECG/EMG cable and guarantee reliable ECG/EMG signal transmission for comprehensive cardiac monitoring. Trust in the accuracy and convenience of this setup to effortlessly record electrocardiograms and electromyograms with confidence.

EEG Click accessories image

Used MCU Pins

mikroBUS™ mapper

Analog Output
RA2
AN
NC
NC
RST
NC
NC
CS
NC
NC
SCK
NC
NC
MISO
NC
NC
MOSI
NC
NC
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

EEG Click Schematic schematic

Step by step

Project assembly

EasyPIC v7a front image hardware assembly

Start by selecting your development board and Click board™. Begin with the EasyPIC v7a as your development board.

EasyPIC v7a front image hardware assembly
GNSS2 Click front image hardware assembly
MCU DIP 40 hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
EasyPIC v7a 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 EEG Click driver.

Key functions:

  • eeg_read_an_pin_value - This function reads results of AD conversion of the AN pin

  • eeg_read_an_pin_voltage - This function reads results of AD conversion of the AN pin and converts them to proportional voltage level

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 EEG Click Example.
 *
 * # Description
 * This example demonstrates the use of EEG Click board.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes Click board.
 *
 * ## Application Task
 * Reads ADC value and sends results on serial plotter every 5 ms.
 *
 * @author Jelena Milosavljevic
 *
 */

#include "board.h"
#include "log.h"
#include "eeg.h"

static eeg_t eeg;   /**< EEG Click driver object. */
static log_t logger;    /**< Logger object. */
uint32_t time = 0;

void application_init ( void )
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    eeg_cfg_t eeg_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 " );
    log_printf( &logger, " ----------------------------------------------\r\n" );
    log_printf( &logger, "                ***EEG click***               \r\n" );
    log_printf( &logger, "----------------------------------------------\r\n" );
    Delay_ms( 2000 );
    
    // Click initialization.
    eeg_cfg_setup( &eeg_cfg );
    EEG_MAP_MIKROBUS( eeg_cfg, MIKROBUS_1 );
    if ( ADC_ERROR == eeg_init( &eeg, &eeg_cfg ) ){
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );
    }
    log_info( &logger, " Application Task " );
}

void application_task ( void ) 
{
    uint16_t eeg_an_value = 0;
        
    if ( eeg_read_an_pin_value( &eeg, &eeg_an_value ) != ADC_ERROR ) {
        log_printf( &logger, " %u,%lu\r\n", eeg_an_value, time );
        Delay_ms( 5 );
        time += 5;
    }
}

void main ( void ) 
{
    application_init( );

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

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

Additional Support

Resources