Plugapod Analog in

[ddlawrence]

Hi. I am logging pitot air pressure and have noticed that on BOTH my Pods, AD0 has consistently good accuracy (less than 1% error, which is acceptable), AD1-AD6 is about 1.5% error and AD7 has about 4% error. These results come from averaging and logging 10000+ samples. Has anyone else noticed this? May it be the DSP56F803 layout or I damaged them? btw, these results are with no circuitry attached.

thanks.........don

[RMDumse]

No, we haven't noticed the pattern you mention. We've noticed the A/D ports occassionally look noisier than we'd expect with 12-bits of supposed accuracy.

You might want to search Freescale literature. I remember something about A/D accuracy in an appnote. But details don't come to mind.

Unlikely to be the layout. Unlikely you've burned them out. More likely something like conversion order or the like.

Sorry not more help. Maybe someone else has noticed this pattern of channel differences? Anyone comment?

[RMDumse]

Think this is the app note I was remembering. Haven't detail-reread it yet. Scanning makes me wonder if we have noise on the Vref pin. Maybe additional capacitance on those pins would help. See if this app note is of any help.

http://cache.freescale.com/files/product/doc/AN1947.pdf?fpsp=1&WT_TYPE=Application Notes&WT_VENDOR=FREESCALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation