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A/D problem

 
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Bilal



Joined: 24 Apr 2010
Posts: 75
Location: Islamabad

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A/D problem
PostPosted: Thu Oct 21, 2010 11:12 pm     Reply with quote
Hi. I am using PIC16F877A. I want to use 2 A/d channels at the same time. One for temp sensor and other for voltage measurements (simple a variable resistor).
The problem is one both are not independent (I guess).
Voltmeter value is changing with temp sensor value.

This is my code
Code:

void main()
{
float value;
float volts;
int decic,TC,TF,decif;
float tempc,read,tempf;

setup_port_A( ALL_ANALOG );
setup_adc( ADC_CLOCK_INTERNAL );
   
lcd_init();

do{
set_adc_channel(1);
read = Read_ADC();

tempc=read*1.5;

tempf=(1.8*tempc)+32;

lcd_gotoxy(1,2);
printf(lcd_putc,"Temp %f C",tempc);

set_adc_channel(0);
value = Read_ADC();
volts= value/51;

lcd_gotoxy(1,1);
printf(lcd_putc,"Volts %f",volts);

   } while (TRUE);
}

Please kindly help me with this problem.
thanks
_________________
...
Wayne_



Joined: 10 Oct 2007
Posts: 681

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PostPosted: Fri Oct 22, 2010 1:45 am     Reply with quote
if you look at CCS help it will tell you what is wrong!

You need a 10us delay after switching channels :-

Code:

set_adc_channel(2);

delay_us(10);

value = read_adc();


The delay may need tweaking depending on your hardware.
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