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Trent
Joined: 13 Apr 2004
Posts: 2
Location: Melbourne, FL
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| Unstable 10bitA/D on 16F819: On 0v it varies up to 0.2v etc |
 Posted: Tue Apr 13, 2004 2:10 pm |
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I have a PIC16F819 based project driven by a 8MHz ext osc. I use Interrupts to keep track of two independent RPMs and I use four 10Bit A/Ds. The code below has erratic A/D results that are typically 0.2v from the correct value and jump around in every 10ms packet to the RS232 port.
Example output with a 3volt input and 5v on the ref pin RA3: [readings every 10ms]
3.05
3.12
3.03
3.11
2.87
3.03
etc
Without the interrupt code in place the readings were rock solid on the same platform. I can also revert back to just the A/D code and have it solid.
Here is the code:
==================
| Code: | #include <16F819.H>
#use delay(clock=8000000)
#use rs232(baud=57600,xmit=PIN_B3,rcv=PIN_B0)
// Timing Vars //
int16 int8_Timer0_Rolls; // Number of times Timer0 has rolled from 254,255,0,1,2,3
int8 int8_LED_Counter; // For LED "alive" Blinking
int1 int1_Power_Light_Blink; // For LED "alive" Blinking also
int16 int16_counter_rs232; // Packet Counting Var
// ADC Vars //
int16 int32_ADC_A;
int16 int32_ADC_B;
int16 int32_ADC_C;
int16 int32_ADC_D;
int8 int8_IntCounter_RB5; // Interrupt Counter 1
int8 int8_IntCounter_RB7; // Interrupt Counter 2
int1 int1_IntCounterFlag_RB5; // Interrupt Counter 1 Flag
int1 int1_IntCounterFlag_RB7; // Interrupt Counter 2 Flag
#int_RB
// External Interrupt on Interrupt Pin RB4-RB7 //
interrupt1_trigger() {
// Find which pin triggered the interrupt RB4-7 //
if(input(PIN_B5)==1) { // Interrupt because of Pin B5 //
if(int1_IntCounterFlag_RB5==0){
++int8_IntCounter_RB5;
int1_IntCounterFlag_RB5 = 1;
OUTPUT_HIGH(PIN_B6); // Blink Yellow LED
}
}else{
int1_IntCounterFlag_RB5 = 0; // Unlatch Debounce //
}
if(input(PIN_B7)==1) { // Interrupt because of Pin B7 //
if(int1_IntCounterFlag_RB7==0){
++int8_IntCounter_RB7;
int1_IntCounterFlag_RB7 = 1;
OUTPUT_HIGH(PIN_B1); // Blink Green LED
}
}else{
int1_IntCounterFlag_RB7 = 0;
}
}
// Timer Overflow Interrupt //
#int_rtcc // This function is called every time
clock_isr() { // the RTCC (timer0) overflows (255->0).
int8_Timer0_Rolls++;
SET_TIMER0(100); // Timer0 needs to roll every 10ms [Exactly] //
if(int8_LED_Counter++>100) { // Blink LED every Second as "alive" communication //
if(int1_Power_Light_Blink==1) {
OUTPUT_HIGH(PIN_B1); // Green //
int1_Power_Light_Blink=1;
int8_LED_Counter=0;
} else {
int1_Power_Light_Blink=1;
int8_LED_Counter=0;
}
}
}
main() { // Main Settings //
int8_Timer0_Rolls = 0;
// Clear Interrupt Vars //
int8_IntCounter_RB5=0;
int8_IntCounter_RB7=0;
int1_IntCounterFlag_RB5=0;
int1_IntCounterFlag_RB7=0;
int16_counter_rs232=0; // Clear Packet Counter Var
Port_B_Pullups(FALSE); // TRUE Pulls B Ports up to 5v False leave them at 0v.
set_rtcc(0);
setup_timer_0( RTCC_INTERNAL|RTCC_DIV_128);
//setup_timer_0( RTCC_INTERNAL|RTCC_DIV_2); // Old value from 4mhz RC Clock
enable_interrupts(RTCC_ZERO);
enable_interrupts(INT_RB);
enable_interrupts(GLOBAL);
// Setup ADC Ports //
// RA3 is tied to +5v ref voltage //
setup_adc_ports(A_ANALOG_RA3_REF); // RA0 RA1 RA2 RA5 RE0 RE1 RE2 Ref=RA3 RA3=Pin 2 +5V Ref
//setup_adc(ADC_CLOCK_INTERNAL); // Tried this, no help //
setup_adc(ADC_CLOCK_DIV_32);
while(TRUE) {
if(int8_Timer0_Rolls > 0) { // This happens every 10ms //
int8_Timer0_Rolls=0;
// Turn Off LEDs every 10ms //
OUTPUT_LOW(PIN_B6); // LED 2 OFF = Pin B5/A6 //
OUTPUT_LOW(PIN_B1); // LED 1 OFF = Pin B1/B4 // B4 Low + B1 High = Green
// ADC Data Collection //
delay_us(50);
SET_ADC_CHANNEL(0); // RA0 //
delay_us(50);
int32_ADC_A = READ_ADC();
SET_ADC_CHANNEL(1); // RA1 //
delay_us(50);
int32_ADC_B = READ_ADC();
SET_ADC_CHANNEL(2); // RA2 //
delay_us(50);
int32_ADC_C = READ_ADC();
SET_ADC_CHANNEL(4); // RA4 //
delay_us(50);
int32_ADC_D = READ_ADC();
// Send Data Frame every 100ms //
printf("S%4LX%4LX%4LX%4LX%4LX%4LX%4LXL",int8_IntCounter_RB5,int8_IntCounter_RB7,int32_ADC_A,int32_ADC_B,int32_ADC_C,int32_ADC_D,int16_counter_rs232++);
if(int16_counter_rs232>1000) {
int16_counter_rs232=1;
}
} // If Timer0 Rolls //
} // While Loop // |
Any help would be greatly appreciated! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Apr 13, 2004 3:40 pm |
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I notice that your interrupts are turning LEDs on and off.
I wonder what this is doing to the external Vref voltage ?
Is it it drooping momentarily when an LED is turned on ?
You could test this theory by commenting out the lines of
code in your ISR that turn the LEDs on and off.
See if that fixes the problem.
Could the A/D input voltages also be affected by turning
the LEDs on and off ? |
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Trent
Joined: 13 Apr 2004
Posts: 2
Location: Melbourne, FL
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| It was the 8MHz Ext Osc AND the LEDs causing the noise |
| Posted: Tue Apr 13, 2004 9:56 pm |
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Thanks PCM Programmer,
Now the LEDs was a simple fix, I just flash them MUCH faster, less power, less noise.
The ext oscillator was chosen because of my critical need for exactly 10ms between packets [RS232 printf’s]. The internal RC [INTRC] is not calibrated very well on some PIC16F819s and thus the timing is off. There seems to be a large variation between actual oscillations at 8MHz, so much so that my RS232 56K has many errors. My solution was to add the Ext Osc. I know I can calibrate the internal osc, but how and in what step would I do that in the manufacturing process?
New Questions:
How do I calibrate the internal RC Osc to 8MHz?
Sample Code?
Thanks again, this was killin me. |
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