NEIL GANDLER wrote:
>
>  I would like to interface an LM34 temperature sensor to one
> of the PIC A/D inputs. My concern is induced noise on the lines
> leading from the LM34 to the PIC chip (about 4 inches of pcb trace)
> The circuitry will be on
> a double sided PCB. On the same board, atleast 3-4 inches away is
> a high current PWM power modulated at 50khz. I am concerned that
> this will cause errors in my LM34 value sensing. I would like to avoid
> using a buffer before the a/d, especially since the LM34 is considered
> to be a low impedence part. I am not sure adding an RC network before
> the PIC input would be
> effective, especially since I need to observe a maximium of 10k input
> impedence. Is runing the LM34 signal line, along with ground lines
> along the side, enough to reduce induced noise problems?
>
> Neil Gandler

You should use an RC filter as at least part of the solution.
Just a cap on the input pin will give you an RC filter
without changing your input impedance
(the input impedence is the R in the RC network)

Also consider feedthrough caps and ferrite beads,
though better for higher frequencys, will have
some effect at 50K.
And its dead easy to slip a small ferrite bead on
a resistor lead, feedthrough lead, input wire
or jumper thats in the signal path
--
Peter Cousens
email: peter@cousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

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