QG8 ADC Woes...

[Ryanst]

I'm really just looking for some input...

I am using the ADC on the chip and it seems to work fine. If I hook a couple of AA batteries up to it the reading fluctuates at most +/-1 between each reading. if I attach ground to it I get a zero back every time and if I plug the demo board power into it I get 1023 steadily as well.

Problem comes in when I try to hook just about anything else up to it... I have an accelerometer from dimension engineering that when it's still it outputs 1.566-1.567V. I can watch it on the multimeter. However, these fluctuations translate into reading changes on the ADC within about 20 points of the actual reading. Just doing some quick math I found that it should fluctuate at most by 1. Same thing happens when I use an ADI Gyro. I was wondering if anyone had an insight as to how to either flatten these fluctuations (without averaging... mainly because it doesn't seem to help whatsoever) or eliminate them altogether.

Thanks.

Ryan

[joerg]

Hi Ryan
How are the output resistances of your sources? Sometimes they are rather high and that may cause your problem, because the input resistance of the AD converter tends to be low (about 5 kOhm). To resolve that problem i normally use a OP to buffer the signal (ie. a LMC6482 rail to rail OP, used as non inverting amplifier).

Saluti Joerg

[Ryanst]

That'a a really good idea. I'll give that a try and report back.

R.