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Sutton Murray
08-31-2008, 11:01 PM
I am taking readings from a LM34 through an ADC. I am experiencing fluctuation readings of up to 6 degrees(jumping around).

I even added a 75 ohm resistor an 1uF cap no real difference.



What may be the reason be for this?

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For in much wisdom is much grief, and he who increases knowledge increases sorrow." ~Ecclesiastes 1:18

Chet
09-01-2008, 12:51 AM
from this and you memsic post, I assume you are using both on or arond an engine. The electrical noise from the electrical system and ignition coils can interfere with the signals. Is everything shielded and decoupled properly.

Sutton Murray
09-02-2008, 03:16 AM
Yes, its for the engine,
Fluctuation on the lm34 occurs on and of (away from the engine). The LM34 is also mounted on the pc board and not on wires.

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For in much wisdom is much grief, and he who increases knowledge increases sorrow." ~Ecclesiastes 1:18

Phil Pilgrim (PhiPi)
09-02-2008, 03:29 AM
If your ADC is referenced to Vdd, rather than to a separate reference voltage, it could be Vdd that's fluctuating and throwing off the LM34 conversion.

-Phil

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'Still some PropSTICK Kit bare PCBs (http://forums.parallax.com/showthread.php?p=729096) left!

Sutton Murray
09-02-2008, 04:40 AM
Mmm DC-DC converter switch driving the ADC. Thanks for the clue, i will be looking into that.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
For in much wisdom is much grief, and he who increases knowledge increases sorrow." ~Ecclesiastes 1:18