ADC PROGRAMMING USING PIC184550

ADC Analog to Digital Converter:

We all know how analog to digital converter works. It’s simple

There are 3 steps:

1.)           Find the resolution of ADC i.e. in our case it’s 10-bit. Let us assume n = resolution. So n =10.

2.)           Find the Step Size using the formula:

Step Size = (V_ref) / (2ⁿ – 1)

       We Know V_ref = (V₊ ) – (V_-), i.e. V₊ is connected to

         V_cc = +5V and V_- is connected to V_ss = GND

        By ADCON1 Register we can assign V_ref for PIC18

        So Formula is converted as follow:

        Step Size = (V_cc) / (2¹⁰ - 1)

                        = (V_cc) / (1023) ; if V_cc = +5V

                        = (5) / (1023)

        Step Size = (0.004887585532746823069403714565)

3.)           Find the Digital out i.e. it varies from 0 – 1023.

D_out = (V_in) / (Step Size)

   Here V_in is the input analog voltage which is given to AN0 –            AN12 i.e. 12 Channel in PIC18 for ADC.

   Now Formula for V_in = 5

D_out = (5) / (Step Size); D_out = 1023 which is 3FF H

    

   If V_in = 2.5

   

        D_out = (2.5) / (Step Size); D_out = 511.2 ≈ 511 i.e. 1FF H

     So in this way we can get all the digital value for analog input.

In PIC18 we have an inbuilt ADC with 10-bit resolution.

There are 3 control register associated with PIC18 i.e.

1.)           ADCON0.

2.)           ADCON1.

3.)           ADCON2.

1.) ADCON0:

Bits	7	6	5	4	3	2	1	0
	--	--	CHS3	CHS2	CHS1	CHS0	GO/DONE	ADON
Value	0	0	0	0	0	0	0	1	0x01

ADON = 1; Enable ADC Module in PIC18

CHS3 – CHS0 = 0000 – 1100; (Analog Channel Select bits) 12 channel for ADC. [Channel Zero is selected in this Case]

Go/Done = A/D Conversion Status

Go = 1; Start of Conversion [Write]

Done = 0; Read this for Zero, i.e. End of Conversion.

2.) ADCON1:

Bits	7	6	5	4	3	2	1	0
	--	--	VCFG1	VCFG0	PCFG3	PCFG2	PCFG1	PCFG0
Value	0	0	0	0	1	0	0	1	0x09

VCFG1= 0; Voltage Reference Configuration bit (VREF- source) V_cc

VCFG0= 0; Voltage Reference Configuration bit (VREF+ source) V_DD

PCFG3– PCFG0= 0000 – 1111; (A/D Port Configuration Control bits)

To select 15 I/O Lines of PIC18 as Digital or Analog we must configure it. [In this case AN0 – AN5 as Analog, but we can configure it as we wish]. Refer Data Sheet of PIC18F4550

3.) ADCON2:

Bits	7	6	5	4	3	2	1	0
	ADFM	--	ACQT2	ACQT1	ACQT0	ADCS2	ADCS1	ADCS0
Value	1	0	1	0	1	1	0	1	0xAD

ADFM: A/D Result Format Select bit

1 = Right justified

0 = Left justified

ACQT2:ACQT0: A/D Acquisition Time Select bits

101=12 T_AD

ADCS2:ADCS0: A/D Conversion Clock Select bits

101 = FOSC/16

There are two 8bit Register to store ADC’s 10bit Output.

1.)           ADRSEL.

2.)           ADRESH.

Right Adjust Means:

ADRESH:                             

15	14	13	12	11	10	9	8
x	x	x	x	x	A	A	A

ADRESL:

7	6	5	4	3	2	1	0
A	A	A	A	A	A	A	A

     

Only 0-10 bit of Register ADRESH & ADRESL are occupied if Right Adjust is used. For Left Adjust it 15-5 bits of ADRESH & ADRESL.

Now for Programming Follow Step are used.

Step 1: Create lcd.h file for lcd function to display all data.

                Refer previous videos for lcd.h and Blog.

Step 2: Create adc.h file for adc function.

1.)           Initialize ADCON0 , ADCON1, ADCON2

2.)           Write Function to start the conversion and return the output digital data.

3.)           Write function to display all digital output in LCD

Step 3: Create main.c file and call all fnction in it.

         Step 1: Declaration of input and output port.

         Step 2: Call LCD and adc initialization function

        Step3: In while continuous read all data from adc and display it in LCD.

Thank You for Reading .

Check Out Video for Above Description: Click for video on ADC

ADC using PIC Code: Click Here For Code

Pic18 Data sheet:Click for Datasheet