Problem with RCTIME.

Archiver

I have conected up 2 Thermistors (NTC) and want to read there values
with a BS2.
I use the RCtime command As described in the manual,
The theristor is about 5K okm and I use a 2 micro farad cond. for
charge.

The problem is that the readings differs all the time ,
If I messure the resistans it is constant, but the debug value differs
for every sampel, and it differs a lot......


Has anyone had the same problem .....


Best regards

Tore Eilertsen

Archiver

Tore,
A while back, I was trying to read a remote potentiometer using RCtime.
Normally, you would want to keep the resistance values low to minimize
noise pickup. I tried to use 5K pots with 2 µF caps (sounds a lot like your
setup!). I found that the readings jumped all over the place. I rewired,
using larger conductor cable, but still had the same results. I coiled up
the wire and brought it right next to the Stamp ..... same problem. I
scaled the pots up to 50K and the caps down to 0.2 µF and everything
settled down with consistent readings from the pots. I'm sure that someone
has documented this. At the time, I couldn't find anything written up on it.
You probably don't want to change your thermistors to 50K values and don't
want to loose the full scale counts by decreasing your caps. Maybe someone
out there has an idea how you can get this "free lunch" with the
thermistors you already have.
That's my $.02 worth. Good luck!
Mike

At 02:15 PM 5/1/2001 +0000, you wrote:
>I have conected up 2 Thermistors (NTC) and want to read there values
>with a BS2.
>I use the RCtime command As described in the manual,
>The theristor is about 5K okm and I use a 2 micro farad cond. for
>charge.
>The problem is that the readings differs all the time ,
>If I messure the resistans it is constant, but the debug value differs
>for every sampel, and it differs a lot......
>Has anyone had the same problem .....
>Best regards
>Tore Eilertsen

_________________________________
Mike Walsh
walsh@i...

Archiver

every thing that I have read to date say's to use a .1uf cap
it's always worked for me but just today I used a .01uf and my values were
way lowwwwww.
so try using a .1uf cap.
just a thought
victor

---

Original Message

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From: "MIKE WALSH" <walsh@c...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, May 01, 2001 2:31 PM
Subject: Re: [noparse][[/noparse]basicstamps] Problem with RCTIME.


Tore,
A while back, I was trying to read a remote potentiometer using RCtime.
Normally, you would want to keep the resistance values low to minimize
noise pickup. I tried to use 5K pots with 2 µF caps (sounds a lot like your
setup!). I found that the readings jumped all over the place. I rewired,
using larger conductor cable, but still had the same results. I coiled up
the wire and brought it right next to the Stamp ..... same problem. I
scaled the pots up to 50K and the caps down to 0.2 µF and everything
settled down with consistent readings from the pots. I'm sure that someone
has documented this. At the time, I couldn't find anything written up on it.
You probably don't want to change your thermistors to 50K values and don't
want to loose the full scale counts by decreasing your caps. Maybe someone
out there has an idea how you can get this "free lunch" with the
thermistors you already have.
That's my $.02 worth. Good luck!
Mike

At 02:15 PM 5/1/2001 +0000, you wrote:
>I have conected up 2 Thermistors (NTC) and want to read there values
>with a BS2.
>I use the RCtime command As described in the manual,
>The theristor is about 5K okm and I use a 2 micro farad cond. for
>charge.
>The problem is that the readings differs all the time ,
>If I messure the resistans it is constant, but the debug value differs
>for every sampel, and it differs a lot......
>Has anyone had the same problem .....
>Best regards
>Tore Eilertsen

_________________________________
Mike Walsh
walsh@i...




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