[Tinyos-help] ADC reading fluctuations

krisa krisatm at gmail.com
Tue Nov 9 01:04:01 PST 2010

A huge thank you!
I Knew just connecting the variable resistor to adc pin and ground
seemed like not the best choice, but didn't know about voltage divider
(as I am quite new to electronics)
With 10 kohm resistor in voltage divider it just worked (I got
readings of approx 2000 while the variable resistor vas strainght
(~10kohm) and approx 3700 when it was bent (~25kohm) So for this
particular use it works well enough, but because I would also like to
get a bit smarter - could you explain how the impedance of ADC input
you mentioned affects the whole thing? And how do I measure it - with
multimeter on ADC/ground pins?
Also If I understand correctly - then simply connecting the ADC to
ground should not have worked at all? And the voltage that I was
reading - that came as a feedback from the ground wire then?

Thanks again!

On Tue, Nov 9, 2010 at 1:31 AM, Michael Schippling <schip at santafe.edu> wrote:
> Less than an order of magnitude off...
> Not bad for failing memory circuits.
> I think the ATMEGA might have been around 250K.
> Or maybe the 165f818 PIC...
> MS
> Yong, Chee Yeew wrote:
>> Not being a lot of help here, but I measured / calculated the input
>> impedance of the MDA300 ADC input recently, and it gave me 500kOhms.

Krišjānis Nesenbergs

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