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 = (Vref)
/ (2n – 1)
We Know Vref = (V+ ) – (V-),
i.e. V+ is connected to
Vcc = +5V and V- is connected to
Vss = GND
By ADCON1 Register we can assign Vref for
PIC18
So Formula is converted as follow:
Step Size
= (Vcc) / (210 - 1)
=
(Vcc) / (1023) ; if Vcc = +5V
=
(5) / (1023)
Step Size = (0.004887585532746823069403714565)
3.)
Find the Digital out i.e. it varies from 0
– 1023.
Dout = (Vin)
/ (Step Size)
Here Vin is the input analog voltage which
is given to AN0 – AN12 i.e. 12 Channel in PIC18 for ADC.
Now Formula for Vin = 5
Dout = (5) / (Step
Size); Dout = 1023 which is 3FF H
If Vin = 2.5
Dout
= (2.5) / (Step Size); Dout = 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) Vcc
VCFG0= 0; Voltage Reference Configuration bit
(VREF+ source) VDD
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 TAD
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:
ADRESL:
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
