LM35 sensor affecting the other analog readings. why?

[ferkar]

hi everyone,

after 2 weeks working on my project i could not improve on lm35 problem.

here is my (or pic's) problem.

At analog channels AN0 and AN1 there is a potansiometer(4,7K) and a lm35 sensor. nad i am displaying these data on a LCD.

when i energize the my sysytem i see that lm35 readings floats . and if i turn the potansiometer it affects lm35 readings.

it means analog channels affect each others.

by the way if i remove lm35 and replace it by another pot everything works well.!

so i am so confused ...

[Ttelmah]

How long are you waiting between changing analog channels?.
The ADC input on the PIC, is effectively a capacitor. This take _time_ to charge to an applied voltage. How long, depends on the impedance of the source, and what voltage was last applied. If you switch too quickly between channels, the last voltage on the capacitor, will affect the new reading...

Best Wishes

[ferkar]

my adc setup: clock_dıv_by_32
waiting between channel selection 100us
Vref+=5V
Vref-=GND

10mV< lm35 output<1500mV
and the main question:
why did i get true results from 2 different potansiometers unlike the results from 1 potonsiometer and lm35?

[SherpaDoug]

Can you tell if the LM35 might be oscillating? Make sure you are using the bypass caps recommended in the LM35 data sheet. If it is oscillating at very high frequencies it could cause strange effects.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[RLScott]