ADC Problem still continues

[No_Fear]

<font face="Courier New" size=-1>Hi,

I'm still in trouble with adc function of 16F877A.I am using port A0,A1,A5,E0,E1,E2.When i measure voltage between ports and GND they are usually at 1 milivolt or 2 milivolts.But when i log them adc function returns 100-120 values equals to 2.0V - 2.5V.When i measure E2 it gives 50 milivolt when i dont apply voltage on it(when idle i mean)!! My device does not work properly now please help!!

No_Fear

My code :

#include <16F877A.h>
#device adc=8
#use delay(clock=4000000)
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)


void main() {

int v1,v2,v3,v4,v5,v6;
char ON;

setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_INTERNAL);
setup_psp(PSP_DISABLED);
setup_spi(FALSE);
setup_counters(RTCC_INTERNAL,RTCC_DIV_2);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
set_tris_d(0x00);

ON = 1;
printf("3A75D5FA\r\n");

while (1)
{

delay_ms(500);

set_adc_channel( 0 );delay_us(100);v1 = read_adc();delay_us(100);
set_adc_channel( 1 );delay_us(100);v2 = read_adc();delay_us(100);
set_adc_channel( 4 );delay_us(100);v3 = read_adc();delay_us(100);
set_adc_channel( 5 );delay_us(100);v4 = read_adc();delay_us(100);
set_adc_channel( 6 );delay_us(100);v5 = read_adc();delay_us(100);
set_adc_channel( 7 );delay_us(100);v6 = read_adc();delay_us(100);

printf("Value:\%2X/\%2X/\%2X/\%2X/\%2X/\%2X!",v1,v2,v3,v4,v5,v6);

if (ON == 1) {output_high(PIN_D2);ON = 0;} else {output_low(PIN_D2);ON = 1;}

v1=0;v2=0;v3=0;v4=0;v5=0;v6=0;
}

}


I upload schematic at www.mcu.cz/atm
Follow Home->Schematics->877.gif


Please Helpp!!</font>
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515026

[Tomi]

Do you have any analog voltage on any input pin?
Don't forget that the PIC has only one A/D converter. The analog inputs are multiplexed. After the multiplexer there is a S/H circuit. Let's say the capac. in the S/H is charged to e.g. 2V (from a previously measured analog pin or from an internal circuit like itself the S/H). In this case because the selected analog pin is floating you will measure something proportional with the previous measurement.
Typically, if you have 8 analog inputs and the first is connected to 2.5V and the others are floating, you will get something like this (AD0-7, 8bit mode): 128,100,80,70,60,50,45,42 (the S/H capacitance discharges exponentially).
I always use a big pulldown resistor (e.g. 100k) on analog inputs not only for set the undriven inputs into a definite state but to give chance to S/H circuit to discharge the capacitor over these resistors.

:=I'm still in trouble with adc function of 16F877A.I am using port A0,A1,A5,E0,E1,E2.When i measure voltage between ports and GND they are usually at 1 milivolt or 2 milivolts.But when i log them adc function returns 100-120 values equals to 2.0V - 2.5V.When i measure E2 it gives 50 milivolt when i dont apply voltage on it(when idle i mean)!! My device does not work properly now please help!!
:=
:=No_Fear
:=
:=My code :
:=
:=#include <16F877A.h>
:=#device adc=8
:=#use delay(clock=4000000)
:=#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
:=#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)
:=
:=
:=void main() {
:=
:=int v1,v2,v3,v4,v5,v6;
:=char ON;
:=
:= setup_adc_ports(ALL_ANALOG);
:= setup_adc(ADC_CLOCK_INTERNAL);
:= setup_psp(PSP_DISABLED);
:= setup_spi(FALSE);
:= setup_counters(RTCC_INTERNAL,RTCC_DIV_2);
:= setup_timer_1(T1_DISABLED);
:= setup_timer_2(T2_DISABLED,0,1);
:= setup_comparator(NC_NC_NC_NC);
:= setup_vref(FALSE);
:= set_tris_d(0x00);
:=
:=ON = 1;
:=printf("3A75D5FA\r\n");
:=
:=while (1)
:={
:=
:= delay_ms(500);
:=
:= set_adc_channel( 0 );delay_us(100);v1 = read_adc();delay_us(100);
:= set_adc_channel( 1 );delay_us(100);v2 = read_adc();delay_us(100);
:= set_adc_channel( 4 );delay_us(100);v3 = read_adc();delay_us(100);
:= set_adc_channel( 5 );delay_us(100);v4 = read_adc();delay_us(100);
:= set_adc_channel( 6 );delay_us(100);v5 = read_adc();delay_us(100);
:= set_adc_channel( 7 );delay_us(100);v6 = read_adc();delay_us(100);
:=
:= printf("Value:\%2X/\%2X/\%2X/\%2X/\%2X/\%2X!",v1,v2,v3,v4,v5,v6);
:=
:= if (ON == 1) {output_high(PIN_D2);ON = 0;} else {output_low(PIN_D2);ON = 1;}
:=
:= v1=0;v2=0;v3=0;v4=0;v5=0;v6=0;
:=}
:=
:=}
:=
:=
:=I upload schematic at www.mcu.cz/atm
:=Follow Home->Schematics->877.gif
:=
:=
:=Please Helpp!!</font>
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515029

[No_Fear]

Hi,

I fixed my problem.I remove 100 ohms resistors and zenner diodes and i connect 100 nf cap between gnd and every analog ch.An i connect 2.2 Kohms res. parallelly to capacitors.Now it works well.Thank you.

No_Fear

:=Do you have any analog voltage on any input pin?
:=Don't forget that the PIC has only one A/D converter. The analog inputs are multiplexed. After the multiplexer there is a S/H circuit. Let's say the capac. in the S/H is charged to e.g. 2V (from a previously measured analog pin or from an internal circuit like itself <img src="http://www.ccsinfo.com/pix/forum/smile.gif" border="0"> the S/H). In this case because the selected analog pin is floating you will measure something proportional with the previous measurement.
:=Typically, if you have 8 analog inputs and the first is connected to 2.5V and the others are floating, you will get something like this (AD0-7, 8bit mode): 128,100,80,70,60,50,45,42 (the S/H capacitance discharges exponentially).
:=I always use a big pulldown resistor (e.g. 100k) on analog inputs not only for set the undriven inputs into a definite state but to give chance to S/H circuit to discharge the capacitor over these resistors.
:=
:=:=I'm still in trouble with adc function of 16F877A.I am using port A0,A1,A5,E0,E1,E2.When i measure voltage between ports and GND they are usually at 1 milivolt or 2 milivolts.But when i log them adc function returns 100-120 values equals to 2.0V - 2.5V.When i measure E2 it gives 50 milivolt when i dont apply voltage on it(when idle i mean)!! My device does not work properly now please help!!
:=:=
:=:=No_Fear
:=:=
:=:=My code :
:=:=
:=:=#include <16F877A.h>
:=:=#device adc=8
:=:=#use delay(clock=4000000)
:=:=#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
:=:=#use rs232(baud=9600,xmit=PIN_C6,rcv=PIN_C7)
:=:=
:=:=
:=:=void main() {
:=:=
:=:=int v1,v2,v3,v4,v5,v6;
:=:=char ON;
:=:=
:=:= setup_adc_ports(ALL_ANALOG);
:=:= setup_adc(ADC_CLOCK_INTERNAL);
:=:= setup_psp(PSP_DISABLED);
:=:= setup_spi(FALSE);
:=:= setup_counters(RTCC_INTERNAL,RTCC_DIV_2);
:=:= setup_timer_1(T1_DISABLED);
:=:= setup_timer_2(T2_DISABLED,0,1);
:=:= setup_comparator(NC_NC_NC_NC);
:=:= setup_vref(FALSE);
:=:= set_tris_d(0x00);
:=:=
:=:=ON = 1;
:=:=printf("3A75D5FA\r\n");
:=:=
:=:=while (1)
:=:={
:=:=
:=:= delay_ms(500);
:=:=
:=:= set_adc_channel( 0 );delay_us(100);v1 = read_adc();delay_us(100);
:=:= set_adc_channel( 1 );delay_us(100);v2 = read_adc();delay_us(100);
:=:= set_adc_channel( 4 );delay_us(100);v3 = read_adc();delay_us(100);
:=:= set_adc_channel( 5 );delay_us(100);v4 = read_adc();delay_us(100);
:=:= set_adc_channel( 6 );delay_us(100);v5 = read_adc();delay_us(100);
:=:= set_adc_channel( 7 );delay_us(100);v6 = read_adc();delay_us(100);
:=:=
:=:= printf("Value:\%2X/\%2X/\%2X/\%2X/\%2X/\%2X!",v1,v2,v3,v4,v5,v6);
:=:=
:=:= if (ON == 1) {output_high(PIN_D2);ON = 0;} else {output_low(PIN_D2);ON = 1;}
:=:=
:=:= v1=0;v2=0;v3=0;v4=0;v5=0;v6=0;
:=:=}
:=:=
:=:=}
:=:=
:=:=
:=:=I upload schematic at www.mcu.cz/atm
:=:=Follow Home->Schematics->877.gif
:=:=
:=:=
:=:=Please Helpp!!</font>
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515040