Analog to Digital Converter (ADC) in PIC Microcontroller

ADC_Symbol

Analog to Digital Converter (ADC) in PIC Microcontroller

ADC module of PIC microcontroller have usually 5 input for 28 pin devices and 8 inputs for 40 pin devices. The conversion of analog signal to PIC ADC module results in corresponding 10 bit digital number. PIC ADC module has software selectable high and low voltage reference input to some combination of VDD, VSS, RA2 and RA3.

In the following example project we will convert analog input to channel 1 to 10 bit digital number with low voltage reference (Vref-) 0v and high voltage reference (Vref+) 5V. The output will be displayed using 10 LEDs. You can change the Vref- and Vref+ by configuring the ADCON1 register.

ie,

0v  =  0000000000


5v  =  1111111111

Resolution = (Vref+ – Vref-)/(1024-1)   (as it is 10 bit ADC)

= 5/1023

= 4.887 mV



Thus it means that for a change in 4.887mV, the binary output changes by 1.

Circuit Diagram

Note: VDD and VSS of the pic microcontroller is not shown in the circuit diagram. VDD should be connected to +5V and VSS to GND.

MikroC Program

unsigned int adc;
void main()
{
 ADCON1 = 0x80;
 TRISA = 0xFF; // PORTA is input
 TRISC = 0x3F; // Pins RC7, RC6 are outputs
 TRISB = 0;    // PORTB is output
 do
 {
 adc = ADC_Read(1); // Get 10-bit results of AD conversion
 //of channel 1
 PORTB = adc;      // Send lower 8 bits to PORTB
 PORTC = adc >> 2; // Send 2 most significant                  //bits to RC7, RC6
 } while(1);
}

You can vary the analog input value by varying the resistance of the potentiometer in the circuit.



This tutorial covers only the basic ADC operation. If you want to know more about it, please refer the datasheet of PIC 16F877A. If you have any doubt regarding this please do comment.

Share this post

  • Blinkcruz

    hi..do have a program of it in flowcode?..

  • Sorry …………..
    This link may help you……
    http://www.matrixmultimedia.com/mmforums/viewtopic.php?f=5&t=2562

  • Mahmud Ibrahim

    Very good tutorial.keep posting.
     

  • Aimanbanifadel

    hello ligo ,  the thermometer project show on the lcd temprature : and the value was 414 dgree

  • Aimanbanifadel

    then what is the problem as you think

  • I don’t understand your question…..Please elaborate ……..

  • Aimanbanifadel

    hi, i built the project very good but the result of the lcd is not correct the thermometer does not show the room temperature but show the 414 degree then i need to know where is the problem is it in the hex file or in the sensor ………note (i connect vref+ on5v……..and vref- on 0v) thanks for your care

  • Ligo George

    You needn’t connect +Vref & -Vref………..

    Check the output voltage of the LM 35 temperature sensor..

  • noel george paqueo

    can someome share the code for this project? thanks a lot

  • Code is shared in the article itself…..

  • lusk

    dont u need to set the ansel byte??

  • Nop, There is no register called ANSEL in PIC 16F877A……… it is in PIC 16F877 …

  • jaycee

    hi can you teach me a code for a IR motor speed control. using a program which can read a increment or decrement of speed and will vary the speed of the motor. The increment and decrement is based on the transmitter part of the IR transmitter. thanks a lot 🙂

  • jaycee

    and also there is a LED that will indicate the degree or level how fast the speed of the motor. for example. when you turn on the device, there is only one LED that is on, then when the increment button is pressed, the second LED will turn on. When the decrement button is pressed, the second LED will turn off and will return to only one LED is on.

  • This comment is not related to the above article…..

    Please ask these doubts in our new forum:
    http://www.electrosome.com/forum/

  • sandeep bhardwaj

    Hii…In every tutorial different frequency of crystal has been used. but my board contains only 20Mhz crystal….but how will it be posssible to use different frequency crystal at the same for the two applications which are going to be perfermed simultaneously.

  • I have used 8MHZ crystal for most of the projects and tutorials…
    You can use 20MHZ, simply by changing the oscillator frequency in MikroC settings… before compiling…

  • romli

    how to get 8 bit adc?

  • Neglect the least significant 2 bits…

  • syera

    hi my company have given me a task to create analog to digital converter with max input voltage 12v and min input voltage 5v. but the output must be in 2 bit. meaning that if input 12 v,the output will be 11 and so on. can u help me?

  • You may use above adc with 5 and 0 voltage references…. you can scale down the voltage upto 12V with in 0-5V range using potential divider…
    If you don’t wish to use microcontroller.. you can use R-2R ladder adc …

  • susmitha

    can you please post the corresponding digital outut for the given analog voltages for the above program?

  • I already described it in the article…
    0V – 0000000000
    4.887mV – 0000000001
    9.774mV – 0000000010
    .
    .
    .
    4999.401mV – 1111111111

  • albhee

    TRISA = 0XFF; this code set all pin of port A as input. what have to do to set a single pin of port A as input? which pins can be used to ADC input?

  • ADC inputs are determined by the ADCON1 register… read its datasheet there is a table under ADCON1 register.

  • albhee

    sorry. i mean, what if i want to use some pin of port A as output? how can i set some pin as input and some as output at a time of Port A?

  • Ya sure.. configure the required pins as digital using ADCON1 register and configure those digital pins as output using TRIS register

  • Spider

    Hi, I have gone through your volt and currnet measurement. I have voltage range from 0-50 and current range from 0-1A. As per you calculation presented I get very poor resolution. Can you please explain how to get better resolution through the range using 10 Bit ADC

  • The total resolution will be equal to 50/1023 (+Vref- -Vref)/(2^10)
    so to increase the resolution either you should reduce the voltage range or.. increase the output bits..

  • Bitesh Tiwari

    why the following instruction is written in the above code?

    CMCON = 0x07;

  • It is used to disable internal comparators… i will work without that statement as comparators will be disable by default..

  • ASIM SHERDIL

    i want to convert analog voltage to digital voltage by increasing the input voltage by potentiometer, what should i do ?

  • connect the fixed points of VDD and VSS and variable point to adc input.

  • DIPCAE

    I believe there is error in the program RC7 and RC6, are no connected.

  • DIPCAE

    Hi albhee, 0xff (HEX) = 11111111 (BIN) = 75643210 (Ports number), if you want only one 00000001 = port 0 input also if want anhother 00001000 = port 3 input..

  • DIPCAE

    76543210

  • Yasantha Niroshan

    i already write to same cods for microwc. but cant configure,coming errores ?? plz answer me………

  • komal
  • bahrey58
  • Hello, I can’t find any details about GH-300RT.

  • bahrey58

    sorry i means GH-311RT

  • bahrey58

    sorry i mean GH-311RT ultrasonic sensor

  • Sorry we haven’t any tutorials for GH-311RT.

  • joynal

    Hi,

    I am using PIC16F877A .

    My problem is ANSEL is not support PIC16F877A , but support ADCON .
    i don’t know how to configure

    code is here:

    ANSELC = 0; // Configure PORTC as digital I/O
    ANSELB = 0; // Configure PORTB as digital I/O
    ANSELD = 0; // Configure PORTD as digital I/O

  • Please read the ADC section of PIC 16F877A microcontroller .

  • manoj

    how set 4bit 8bit ad conversion

  • What do you mean ?

  • Harikrishnan

    I have two analog inputs i want to convert the analog input to digital output paralelly is there any possibility to do that so. if it is poosible how can it be done

  • You can’t convert both analog inputs parallelly using PIC ADC.
    But you can convert it sequentially …. one after the other.

  • Ummi Gowda

    what is the meaning of adcon=0x80 please explain me in detail

  • Check the datasheet of 16F877A.. you can find ADCON1 register there….
    It sets all PORTA pins as Analog Inputs.

  • reindy

    Hy, i have some probem to make program in pic16f877. how to read the analog (voltage) sensor. i must measure the RST phase. please help. thank

  • That is what described in the above article.

  • LEGEND

    hi mr.ligo how to make if/else statement to detect condition from adc data?

  • LEGEND

    @lijoppans:disqus

  • You can simply compare the adc values as like normal comparison statements, there is no difference.

  • In MikroC, you have to use IntToStr() to convert integer to string.

  • Omais Ahmed

    hi Ligo
    how to read 16bit value from adc?

  • Seshu Gnaneswar

    sir i just started working with pic micro controller.How can i compare the output of ADC of pic with some other peripheral

  • PIC 16F877A ADC is 10 bit only. If you need 16 bits, try another microcontroller or external ADC.

  • like this :
    a = ADC_Read(0)

    if(a > 10)
    do some thing

  • Ezhil Arasan

    Hi Bro,what is the difference between MIKRO C and Hitech C?Which is best for reduced file size ?

  • Ezhil Arasan

    In ADC program for MIKRO C ADC_ON bit of ADCON0 register is not set .So ADC does not ON.Also ADCON1 register is not declared.The function adc=ADC_read(1) is also not defined.Am I right BRO…waiting for ur answer.. 🙂

  • Hi-Tech C is a deprecated compiler, no longer supported by Microchip. Use MPLAB XC8 instead.
    MikroC is a compiler by Mikroelectronika.

    I think it is better to go with MPLAB XC8 for professional projects.

  • Those will be automatically done by those functions. That is the advantage of mikroc.

  • Matrix

    Thank you Mr. Ligo. I have a doubt. Suppose if i am having two analog voltages and if the difference between the voltages is more (than say, 15mV), then the output should be high otherwise low.
    Is it possible to do so in ADC (or in inbuilt analog Comparator of PIC18F4550) ??
    Can you please tell me how to do it ?

  • Yes, you can compare voltages using ADC. no problems…. Better to use comparator module.. .it will reduce the processing.

  • Ali ‘Imran Akhyar

    ANSEL = 0;
    ANSELH = 0;
    c1on_bit=0;
    c2on_bit=0;

    hello sir.. how to convert this library to microc compiler using pic16f877a?? thnk you sir..

  • Hi,
    Where do you get that program ? There is no ANSEL in my program. PIC 16F877A has no ANSEL registers.