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DAC help!

 
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gbie



Joined: 22 Apr 2009
Posts: 8

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DAC help!
PostPosted: Thu Apr 30, 2009 1:17 am     Reply with quote
Trying to get my DAC0800 working with my pic16f886 so that I can output audio. I use a function generator to input a sine wave into the ADC and then output it to the DAC. It looks great up until about 800Hz and then it starts looking really choppy and then a little higher frequencies it can't follow the input. Any ideas what I could be doing wrong?

I tried adding a latch with A1 being the switchy thing, but that didn't help much. So I'm guessing I didn't need to do that. It doesn't work without that.
Code:

#include <16F886.h>

#fuses intrc, NOLVP, WDT, PUT, NOPROTECT

#byte ADCON0 = 0x1F                         //00000011
#byte ADCON1= 0x0                     //left justified Vss, Vdd references

#DEVICE ADC=8                        //returns MSByte
#use delay(clock=1000000)               //1MHz
#byte TRISA = 0x85
#byte PORTA = 0x5
#byte TRISB = 0x86
#byte PORTB = 0x06

//void dac_set(unsigned int dacval);
//void dac_setup(void);

void main() {
    int Ch_An_0;
    int negative_CHA0;
    TRISB =0x00;
    //    setup_vref(VREF_LOW | 6);
    setup_adc_ports( sAN0 |sAN1 | sAN5 | VSS_VDD );
    setup_adc( ADC_CLOCK_DIV_2 );
    set_adc_channel( 0 );      // ADC0 (RA0)
    while(1){
        output_low(PIN_A1);
        Ch_An_0    = read_adc();

        output_b(Ch_An_0);
        output_high(PIN_A1); //latch
        delay_us(15);
    }

}
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Apr 30, 2009 1:38 am     Reply with quote
Your oscillator frequency of 1 MHz is the limiting factor. Increase it.
Also the 15us delay will slow down the sampling rate. Reduce it.

Also, you have the Watchdog enabled but you're not clearing it.
Change it to NOWDT. You don't need it during development.

Your address of 0x0 for ADCON1 is not correct.
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