AVR-Chat

Is it 24 bit accuracy or 24 bit resolution?  At 24 bits, 1 part in 
almost 17 million...where do we get a reference that accurate with a 
reasonable cost suitable for a weigh scale product?

I suspect 12 bit accuracy would be plenty accurate for your application 
and you wouldn't have the thermal emf problems as with 24 bits.  Just 
throw the lower bits away after you average them into your equations.

On a regular basis here, we take data points and store them in a moving 
average filter.  There's a very good application note both from Atmel 
and at AVRFreaks which describes the process.  If it were me I'd use the 
upper 16 bits of your A/D converter, store those in 2 8 bit registers, 
add that to the 2 registers you have already set up for your averaging 
filter, add the overflow bit to another register set up for that 
purpose, and then after your predetermined number of sample points take 
an average.  It's as simple as that.

You'll also have to adjust the limits of your filter to allow for wind 
gusts or other vibration sources so they don't drive your gizmo wild.


REB

kernels_nz wrote:

>Hi there, this one is out of left field a bit (Baseball phrase ???)
>but im working on a weigh-scale project that uses a 24-bit ADC and I
>was just wondering whether anyone had ever written a weigh-scale
>module for a 8-bit micro controller.
>
>Im just interested to see how all the calibration etc. for finding the
>actual displayed weight from having 32 bit numbers representing the
>Calibration Zero and Span values and the current ADC value. Is there a
>way to do all the calculations without using floating point math? 
>
>Cheers for any information!
>Hein B - Auckland, New Zealand
>  
>