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PSoC 5, 3 & 1 MCU

Anonymous
Not applicable

New to the forums, just started using PSoC and the board that I have. Currently working an small project, as we are supposed to use an on board potentiometer to adjust an  on board LED brightness. We are also supposed to report the 16 bit value to the LCD character display. I have managed to perform both of these steps, however there appears to be some sort of noise, as my least significant digit fluctuates.

   

 

   

Source Code:

   

 int main()

   

{

   

LCD_Char_Start();

   

PWM_1_Start();

   

    ADC1_Start();

   

    Clock_1_Start();

   

    uint16 ADC_Val;

   

    char buffer[5];

   

    

   

    for(;;){

   

        ADC_Val=ADC1_Read16();

   

        PWM_1_WriteCompare(ADC_Val/65);

   

        sprintf(buffer,"%04x",ADC_Val);

   

        LCD_Char_Position(0u, 0u);

   

        LCD_Char_PrintString(buffer);

   

 

   

    }

   

}

   

Any suggestions?

   

Thanks in advance.

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2 Replies
ETRO_SSN583
Esteemed Contributor

If you are running at 16 bit resolution, and a Vref of Vdd then each

   

lsb is ~ 76 uV. Use a DSO, look at Vdd, set it to infinite persistence,

   

and you will probably see ~ 200 mV to 400 mV of noise. Translate

   

that to lsbs =~ 2800 lsbs of noise.

   

 

   

So bypassing is critical, see references below. Use Polymer Tants

   

as they are ~ 10 x better f vs Z performance.

   

 

   

Also plan on A/D pin input not next physically to pins switching a lot

   

of digital I/O.

   

 

   

    

   

         

   

http://www.cypress.com/?rID=39677     AN57821 - PSoC® 3, PSoC 4, and PSoC 5LP Mixed Signal Circuit Board Layout Considerations

   

http://www.cypress.com/?rID=40247     AN58827 - PSoC® 3 and PSoC 5LP Internal Analog Routing Considerations

   

http://www.cypress.com/?rID=39974     AN58304 - PSoC® 3 and PSoC 5LP – Pin Selection for Analog Designs

   

 

   

 

   

Another thing you can do is averaging N samples, for uncorrelated noise you can

   

get significant "filtering" from this, acts as a LPF.

   

 

   

 

   

 

   

Regards, Dana.

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ETRO_SSN583
Esteemed Contributor

Here are some additional ap notes on noise and errors that may be useful -

   

 

   

www.dropbox.com/s/ruaf9booe17jk8n/PCB%20Layout.zip

   

 

   

Regards, Dana.

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