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Date: 07/17/03 at 4:31 AM
Posted by: Geoffrey
E-mail: g_swales@biodigital-limited.com

In Reply to: Eliminating Ground Vibrations in a electronic weighing scale posted by Prashanth.T.G on 07/16/03 at 7:41 AM:

Hello,
It's good practice to low-pass filter any signal going in to an ADC to prevent 'Aliasing'.
You can either use a analog low-pass filter (such as a resistor/capacitor) or you can use software techniques (plenty of samples and take the average).
The last technique is easiest;

scale_adc=GetADC();
ave_adc=((7*ave_adc)+scale_adc)/8;

it's a sort of weighted average.
The 'divide by 8' can be done with a triple shift right (>>3).
Try different numbers so long as the number of samples is the same a the denominator(7+1 = 8)

Things to watch for: reduced response, processor time for multiply, rounding errors(dropping bits).

Regards,

Geoffrey.

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