ARM- ADC and LCD Interface

In real world all natural quantities like temperature, pressure, light intensity etc. are analog. If we have to deal with such quantities using embedded systems, we have to convert these analog quantities which can be understood and proceed by digital signal. Devices used for this purpose is known as ADC. Special ICs such as ADC0804, ADC0808, ADC0809, Serial ADC MAX1112 etc. are handy for this. Nowadays, many controllers are having inbuilt ADC. LPC2138 of ARM7 family is one of the widely used controller and it also has multichannel ADC inbuilt. In this article, we will understand how to use inbuilt ADC of LPC2138.

ADCs acts as a bridge between the ANALOG real world and digital world of controllers. ADC converts analog voltage into a digital number which can be understood and proceed by controller. Let us understand this with an example.

LPC 2138 operates on 3.3V supply. If we use 10 bit ADC, 3.3V correspondences to 2^10=1023. Half of 3.3V= 1.65V can be represented by 512, 0V as digital value 0 and so on.

Before proceeding further, let us first understand few basic concepts related to ADC.

1 )  Resolution :

Analog voltage will be converted into a digital number. Number of bits required to store the digital number let say n bits is known as resolution. If a digital number is represented with n bits, the maximum value is 2n . So for 10 bit ADC resolution is 10 bit and maximum value is 210=1023.

2 ) Step Size : 

Minimum voltage which can be distinguished by controller is known as step size.

Step size= Maximum Voltage/ 2n

where n= resolution

For LPC 2138, Maximum voltage=3.3V and n=10, So step size=3.3/1023= 0.0032258064 V = 3.23 mv (Approx.)

Voltage between 0 and 3.23 mV will be identified as same for controller. This identifies the accuracy of ADC.

3 ) Conversion time : 

Converting analog voltage into a digital will not be done immediately. It will take few mili-seconds. Higher the resolution, higher is the conversion time. Now, let us start with ADC of LPC 2138. First let us have quick look at features of it.

· LPC 2138 has two inbuilt ADC modules known as ADC0 and ADC1.

· Maximum resolution of ADC is 10 bit. It is configurable by programming.

· ADC0 has 6 channels

· ADC1 has 8 channels

· Both ADC supports maximum clock frequency of 4.5 MHz (Operating frequency decides the conversion time)

Pins required for ADC are as follows.

Let us understand all registers one by one : -

The most important register for ADC is ADCR. Let us see the functions of each bit of this register.

The most important register for ADC is ADCR. Let us see the functions of each bit of this register.

 

Another important register is AD0GR and AD1GR. Bits of this register are as follows.

Result of the conversion is stored in A/D Data register which has following structure.

Steps for programming ARM- ADC & LCD Interface : -

1 ) Configure input pin as analog input pin for ADC

2 )  Select channel of ADC

3 ) Start conversion

4 ) Wait till conversion is done

5 ) Read data of ADC Conversion output

6 ) Convert number into separate digits like 512 as separate 5,1 and 2

7 ) Display digits on LCD

8 ) Repeat above steps

The main Code for ARM- ADC and LCD Interface : it uses above lcd.h for lcd interfacing -

#include <LPC213x.h> /* LPC213x definitions */

#include "lcd.h"

void init_adc()

{

        PINSEL1 |= 0X01000000;

        ADCR = 0X00200602;

}

void delay(int n) /* generates one milisecond delay */

{

        int i,j;

        for (i=1; i<=n; i++)

        for(j=0; j<=10000; j++);

}

int read_adc(void)

{

        int val;

        ADCR |= 0x01000000; /* Start A/D Conversion */

        do 

        {

            val = ADDR; /* Read A/D Data Register */

        } while (!(val & 0x80000000)); /* Wait for end of A/D Conversion */

ADCR &= ~0x01000000; /* Stop A/D Conversion */

val >>=6;

val= val & 0x3FF;

return(val);

}

int main(void)

{

        int dat,i=0,int data,int da1=94;

        char buf[6];

        init_adc();

        init_lcd();

        lcd_command(0x01);

        lcd_command(0x80);

        printlcd("ADC Interfacing");

        lcd_command(0xC0);

        printlcd("with LPC2138");

        delay(20);

        lcd_command(0x01);

        lcd_command(0x80);

        printlcd("Digital Value");

        lcd_command(0xC0);

        while(1)

        {

                Delay(1000000);

                lcd_command(0xC0); // dipaying adc data at 2nd line of LCD

                dat = read_adc()*322;

                //data converted into digits

                buf[0]=dat%10;

                dat=dat/10;

                buf[1]=dat%10;

                dat=dat/10;

                buf[2]=dat%10;

                dat=dat/10;

                buf[3]=dat%10;

                dat=dat/10;

                buf[4]=dat%10;

                dat=dat/10;

                buf[5]=dat%10;

                buf[6]=dat/10;

                delay(10);

                lcd_data(buf[6]+'0');

                lcd_data(buf[5]+'0');

                lcd_data('.');

                lcd_data(buf[4]+'0');

                lcd_data(buf[3]+'0');

                lcd_data(buf[2]+'0');

                lcd_data(buf[1]+'0');

                lcd_data(buf[0]+'0');

        }

}

Circuit Diagram For ARM- ADC and LCD Interface : -

LCD Interface with ARM 2138 in 4 bit mode

The various LCD commands used to write data to LCD are given below : -

For Writing to LCD RS, RW and EN pins of a 16character 2 line LCD. It has 8 data pins can be configured in 4 bit and 8bit using proper commands. RS=1 for writing data, and RS=0 for register select for writing special character but for our program it is RS=1.

RW=0 I kept as such as we are writing data. EN=1 for enabling writing for 20 s and then EN=0 disabled.

Steps For LCD Interface With ARM 2138 In 4 Bit Mode

Step 1: initialize the LCD in 4 bit with 2 line.

Step2: create a library for writing a letter or strings.

The library is as follows.

Code For Creating Library For LCD Interface With ARM 2138 In 4 Bit Mode

#include <LPC21xx.h>

void Delay(unsigned long b)

{

    while (--b!=0);

}

void write_command(int cmd)

{

        IO1CLR |= 0x00f00000; // Clear Data pins

        IO1CLR |= 0x00040000; // RW = 0

        IO1CLR |= 0X00020000; // RS= 0,

        IO1SET |= 0x00f00000 & cmd; //Set Data pins

        IO1SET |= 0X00080000; // Enable = 1

        Delay(30000); // Provide Delay

        IO1CLR |= 0x00080000; // Set Enable=0

}

void write_data(int dat)

{

        IO1CLR |= 0x00f00000; // Clear Data pins4-D7

        IO1CLR |= 0x00040000; // RW= 0

        IO1SET |= 0X00020000; //RS= 1

        IO1SET |= 0x00f00000 & dat; // Set Data pins

        IO1SET |= 0X00080000; // Enable = 1

        Delay(30000); //Provide Delay

        IO1CLR |= 0x00080000; //Set Enable=0 

}

void lcd_data(char dat)

{

        write_data(dat << 16);

        write_data(dat << 20);

}

void lcd_command(char cmd)

{

        write_command(cmd << 16);

        write_command(cmd << 20);

}

void printlcd(char *CPtr)

{

        while(*CPtr != 0)

        {

                lcd_data(*CPtr);

                CPtr++;

                Delay(20000);

        }

}

void init_lcd(void)

{

        IO1DIR |= 0x00FE0000;

        Delay(200000) ;

        Delay(100000);

        write_command(0x30 << 16);

        Delay(100000);

        write_command(0x20 << 16);

        lcd_command(0x01); /* clear display */

        lcd_command(0x06); /* auto address inc */

        lcd_command(0x0c); /* cursor off */

        lcd_command(0x28); lcd_command(0x80); /* first location */

}

Then The Main Program For  LCD Interface With ARM 2138 In 4 bit Mode Calling This Header File As Follows To Write A String “Hello World” : -

#include <LPC21xx.h>

#include "lcd.h"

int main(void) 

{

        init_lcd();

        while(1)

        {

                lcd_command(0x01);

                lcd_command(0x80);

                printlcd("Welcome To");

                lcd_command(0xC0);

                printlcd("Hello World");

                Delay(50000000);

        }

}

Circuit Diagram For LCD Interface With ARM 2138 In 4 Bit Mode : -

ARM GPIO Programming- LED Running

 In all GPIO Programming,

First ARM ports are set to input and output using IODIR

For port 0: it will be IODIR0

Port1:IODIR1, and so on

Fr changing data or writing data to pin IOSET command is used

For PORT0: IOSET0 and for PORT 1 it is IOSET1

Similarly for clearing output pin IOCLR is used as in the following program.

Example For ARM GPIO Programming- LED Running : 

#include <lpc213x.h>

void delay_ms(unsigned int count)

{

    unsigned int j=0,i=0;

    for(j=0;j<count;j++)

    {

        for(i=0;i<3000;i++);

    }

}

/* start the main program */

int main()

{ 

    //unsigned int i;

    IODIR1 = 0xffffffff; //Configure the P1 pins as OUTPUT;

    while(1)

    {

        IOSET1=0xffffffff;

        delay_ms(1000);

        IOCLR1= 0xffffffff;

        delay_ms(1000);

    }

}

The Circuit arrangement is as given below