day 3 am adc
TRANSCRIPT
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Introduction to PICMicrocontroller Programming
& Interfacing
August 19-21, 2010Franz Duran
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Analog-to-Digital
Conversion
DAY 3 Morning Session
August 21, 2010
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Analog-to-Digital Conversion
Process of converting an analogsignal to a proportional digital
numberUsed in data acquisition system
Analog-to-Digital ConverterADC, A/D converter
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A/D CONVERSION
Basic 3-bit ADC
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A/D CONVERSION
111+4.375V < Vin
< +5.0V
110+3.75V < Vin
< +4.375V
101+3.125V < Vin
< +3.75V
100+2.5V < Vin
< +3.125V
011+1.875V < Vin
< +2.5V
010+1.25V < Vin
< +1.875V
001+0.625V < Vin
< +1.25V
0000.0V < Vin
< +0.625V
D2D1D0Vin
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A/D CONVERSION
Important ADC propertiesResolution
# of bits higher the # of bits, the better
Conversion time
ADC Architecture
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A/D CONVERSION
Typical A/D converter architecturesFlash ADC
Ramp ADC
Successive Approximation ADC
Integrating slope ADC
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A/D CONVERSION
Example ADC chipNational Semiconductor ADC0804
General purpose application
8-bit resolution
Successive Approximation ADC
10 Ksamples/second (free-running mode)
0-5v input
20-pin DIP
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A/D CONVERSION
BasicADC0804 circuit
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A/D CONVERSION
PIC16F84A
with
ADC0804
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PIC16F A/D MODULE
10-bit resolution
Successive Approximation ADC
0-5V input range
50Ksamples/second
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PIC16F A/D MODULE
SFRs:ADRESH (A/D Result Register High Byte)
ADRESL(A/D Result Register Low Byte)
ADCON0 (A/D Control Register 0)
ADCON1 (A/D Control Register 1)
PIE1 (Peripheral Interrupt Enable Reg. 1)
PIR1 (Peripheral Interrupt Enable Reg. 1)
INTCON (Interrupt Control Register)
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
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PIC16F A/D MODULE
A/D module initialization1. Select A/D Conversion Clock
2. Configure Analog Channels
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PIC16F A/D MODULEvoid ADCInit(void)
{
ADCS0 = 0; //TAD = Fosc/32ADCS1 = 1;
ADCS2 = 0;
PCFG3 = 1; //Only RA0/AN0 is analog input.PCFG2 = 1; //The rest of the analog pins are
PCFG1 = 1; //digital IO
PCFG0 = 0;TRISA0 = 1; //RA0/AN0 is input
CHS0 = 0; //Select channel 0
CHS1 = 0;CHS2 = 0;
ADFM = 1; //Right justified.
...
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PIC16F A/D MODULE
...
...
ADRESL = 0x00; //Clear A/D Result registers
ADRESH = 0x00;
ADIE = 0; //No interruptsPEIE = 0;
GIE = 0;
ADON = 1; //Turn on ADC circuit
return;
}
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PIC16F A/D MODULE
A/D read1. Select Channel
2. Wait Acquisition Time
3. Start A/D Conversion
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PIC16F A/D MODULE//Read the 10-bit A/D value
unsigned int ADCRead(void)
{
unsigned int adc_temp; //Hold the 10-bit A/D value
ADGO = 1; //Start A/D conversion.
while(ADGO == 1); //Wait while conversion is
// not finished.
adc_temp = ADRESL; //Read the lower 8-bit, then
adc_temp += (ADRESH
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PIC16F A/D MODULE
EXERCISE:Open Example#1
Build the project, program the microcontroller, andrun the application
Example#1
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PIC16F A/D MODULEExample#2
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Interfacing LM35 Sensor
LM35National Semicon.
Temp. sensor
T0-92 package
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