Searching \ for 'Interfacing an LM34 temp sensor w/ PIC (noise conc' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/ios.htm?key=sensor
Search entire site for: 'Interfacing an LM34 temp sensor w/ PIC (noise conc'.

Truncated match.
PICList Thread
'Interfacing an LM34 temp sensor w/ PIC (noise conc'
1997\01\23@040153 by NEIL GANDLER

flavicon
face
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

1997\01\23@063015 by peter

flavicon
face
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: spam_OUTpeterTakeThisOuTspamcousens.her.forthnet.gr
snailmail: Peter Cousens, karteros, Heraklion, Crete, 75100, Greece,
phone: + 3081 380534,    +3081 324450   voice/fax

After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem

1997\01\23@195733 by Tony Matthews

flavicon
face
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
Do you have the code space etc. to average several samples ? Tony M.

More... (looser matching)
- Last day of these posts
- In 1997 , 1998 only
- Today
- New search...