AVR-Chat

On Sep 11, 2005, at 8:49 AM, Leon Heller wrote:

>> I have a circuit with an Accelerometer connected to an ATmega32.  The
>> Accel measures 2.5V at rest and goes to .5v or up to 4.5v when  
>> tilted.
>> The motors I am using on this bot cause vibrations when running and I
>> can't get a clean signal fromt he Accel.
>> Is there a way to filter the noise from the motors out of the Accel
>> signal through CodevisionAVR?
>>
>
> DSP might be applicable, if you have enough spare processing  
> capability.

Yes. Unless I read michaelsteinbach's question incorrectly he was  
asking how to do DSP functions using CodevisionAVR.

Maybe after he has tried it he will find the AVR is sufficient. Maybe  
not.

I would suggest a simple averaging of the inputs from the  
accelerometer. If its being shaken then I'd guess half the time its  
going one direction and half the time its going the other direction  
due to vibration. And that the DC offset is the value he is really  
looking for.

Keep a running average. Store a circular buffer of each and every  
sample. Sum the samples as they go in, subtract the old samples as  
they fall off. The average is this value divided by the number of  
samples.

uint16_t samples[COUNT];
uint8_t pos, cnt;
uint32_t sum;

void init_samples(void)
{
     sum = 0;
     pos = cnt = 0;
}

void newsample( uint16_t new )
{
     sum += new;                  //  add to running total
     if( cnt < COUNT ) {
         samples[cnt++] = new;    //  only until samples is full
     } else {
         sum -= samples[pos];     //  remove oldest from running total
         samples[pos++] = new;    //  save the new in oldest space
         if( pos >= COUNT )
             pos = 0;
     }
}

And any time you want to know the average its sum/cnt. If you don't  
mind goofy values the first COUNT samples then remove if( cnt <  
COUNT ) and use sum/COUNT.

void newsample( uint16_t new )
{
     sum += new;
     sum -= samples[pos];
     samples[pos++] = new;
     if( pos >= COUNT )
         pos = 0;
}

--
David Kelly N4HHE, dkelly@HiWAAY.net
========================================================================
Whom computers would destroy, they must first drive mad.