Chapter 11
It’s an Analog World
Learning to use the Analog to
Digital Converter
Analog to Digital Converter
Di Jasio - Programming 32-bit Microcontrollers in C
Reading a Potentiometer
Di Jasio - Programming 32-bit Microcontrollers in C
First Conversion
int readADC( int ch)
{
AD1CHSbits.CH0SA = ch;
AD1CON1bits.SAMP = 1;
T1CON = 0x8000; TMR1 = 0;
while (TMR1 < 100);
AD1CON1bits.SAMP = 0;
while (!AD1CON1bits.DONE);
return ADC1BUF0;
} // readADC
Di Jasio - Programming 32-bit Microcontrollers in C
//
//
//
//
//
//
//
1. select analog input
2. start sampling
3. wait for sampling time
4. start the conversion
5. wait conversion complete
6. read result
Automating Sample Timing
void initADC( int amask)
{
AD1PCFG = amask;
// select analog input pins
AD1CON1 = 0x00E0;
// automatic conversion after sampling
AD1CSSL = 0;
// no scanning required
AD1CON2 = 0;
// use MUXA, use AVdd & AVss as Vref+/AD1CON3 = 0x1F3F;
// Tsamp = 32 x Tad;
AD1CON1bits.ADON = 1; // turn on the ADC
} //initADC
int readADC( int ch)
{
AD1CHSbits.CH0SA = ch;
AD1CON1bits.SAMP = 1;
while (!AD1CON1bits.DONE);
return ADC1BUF0;
} // readADC
Di Jasio - Programming 32-bit Microcontrollers in C
//
//
//
//
1.
2.
3.
4.
select input channel
start sampling
wait conversion complete
read conversion result
First Example: Pot-Man
/*
** Pot-Man.c
**
*/
// configuration bit settings, Fcy=72MHz, Fpb=36MHz
#pragma config POSCMOD=XT, FNOSC=PRIPLL
#pragma config FPLLIDIV=DIV_2, FPLLMUL=MUL_18,
#pragma config FPLLODIV=DIV_1
#pragma config FPBDIV=DIV_2, FWDTEN=OFF, CP=OFF, BWP=OFF
#include
#include
#include
#include
<p32xxxx.h>
<explore.h>
<LCD.h>
<ADC.h>
main ()
{
int a, r, p, n;
// 1. initializations
initLCD();
initADC( AINPUTS);
// 2. use the first reading to randomize
srand( readADC( POT));
// 3. init the hungry Pac
p = '<';
// 4. generate the first random food bit position
r = rand() % 16;
Di Jasio - Programming 32-bit Microcontrollers in C
// main loop
while( 1)
{
// 5. select the POT input and convert
a = readADC( POT);
// 6. reduce the 10-bit result to a 4 bit value (0..15)
// (divide by 64 or shift right 6 times
a >>= 6;
// 7. turn the Pac in the direction of movement
if ( a < n)
// moving to the left
p = '>';
if ( a > n)
// moving to the right
p = '<';
// 8. when the Pac eats the food, generate more food
while (a == r )
r = rand() % 16;
// 9. update display
clrLCD();
setLCDC( a); putLCD( p);
setLCDC( r); putLCD( '*');
// 10. provide timing and relative position
Delayms( 200);
// limit game speed
n = a;
// memorize previous position
} // main loop
} // main
Sensing Temperature
Temperature Sensor connection
on Explorer16 board (DS51589)
Di Jasio - Programming 32-bit Microcontrollers in C
TC1047 Output Voltage vs. Temperature characteristics
Reading Temperature
Averaged temperature reading procedure:
a = 0;
for( j=0; j <10; j++)
a += readADC( TSENS);
i = a / 10;
// add up 10 readings
// divide by 10 to average
Resolving the temperature/voltage equation for T:
T = (Vout - 500 mV) / 10 mV/C
Where Vout = ADC reading * ADC resolution (3.3 mV/bit)
T = ((
i * 3.3) - 500) / 10;
Di Jasio - Programming 32-bit Microcontrollers in C
Second Example: Temp-Man
main ()
{
int a, i, j, n, r, p;
// 1. initializations
initADC( AINPUTS); // initialize the ADC
initLCD();
// 2. use the first reading to randomize
srand( readADC( TSENS));
// generate the first random position
r = rand() % 16;
p = '<';
// 3. compute initial average value
a = 0;
for ( j=0; j<10; j++)
{
a += readADC( TSENS); // read temp
Delayms( 100);
}
i = a / 10;
// average
// main loop
while( 1)
{
// 4. take the average value over 1 second
a = 0;
for ( j=0; j<10; j++)
{
a += readADC( TSENS); // read the temperature
Delayms( 100);
}
a /= 10;
// average result
// 5. compare initial reading, move the Pac
a = 7 + (a - i);
// 6. keep the result in the value range 0..15
if ( a > 15)
a = 15;
if ( a < 0)
a = 0;
// 7. turn the Pac in the direction of movement
if ( a < n)
// moving to the left
p = '>';
if ( a > n)
// moving to the right
p = '<';
// 8. as soon as the Pac eats the food, generate new
while (a == r )
r = rand() % 16;
// 9. update display
clrLCD();
setLCDC( r); putLCD( '*');
setLCDC( a); putLCD( p);
// 10. remember previous postion
n = a;
Di Jasio - Programming 32-bit Microcontrollers in C
} // main loop
} // main