Searching \ for 'A2D problem?' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: techref.massmind.org/techref/io/atod.htm?key=a2d
Search entire site for: 'A2D problem?'.

Truncated match.
PICList Thread
'A2D problem?'
1998\10\28@090530 by Peter Howells

flavicon
face
Good day.
I am new to the pic world and hope you can help.
I'm using a 16C71 to convert 2 analog inputs and then send these
values out the serial port.  The serial comms are working perfectly -
my problem is with the a/d conversion.  As the value on one channel
is adjusted, it affects the other channel, i.e. on the serial output
I get a change in value on both channels as I adjust only one channel
while keeping the voltage on the second channel constant.
Is there a time period that I have to wait between conversions?  The
two inputs that I'm using are RA0 and RA1.
Thanks

Peter Howells
Instrumentation and Control
Department of ELectronic Engineering
Technikon Natal
South Africa

Tel: +27 31 204 2538
Fax: +27 31 204 2063
Email: spam_OUTpeterhTakeThisOuTspamumfolozi.ntech.ac.za

1998\10\28@114606 by Harold Hallikainen

picon face
On Wed, 28 Oct 1998 15:52:25 GMT+200 Peter Howells
<.....PeterHKILLspamspam@spam@UMFOLOZI.NTECH.AC.ZA> writes:
>Good day.
>I am new to the pic world and hope you can help.
>I'm using a 16C71 to convert 2 analog inputs and then send these
>values out the serial port.  The serial comms are working perfectly -
>my problem is with the a/d conversion.  As the value on one channel
>is adjusted, it affects the other channel, i.e. on the serial output
>I get a change in value on both channels as I adjust only one channel
>while keeping the voltage on the second channel constant.
>Is there a time period that I have to wait between conversions?  The
>two inputs that I'm using are RA0 and RA1.


       Yes, there is a minimum required sampling time between when you
set the mux and when you start the A/D.  In my Microchip book, it's on
page 10-114.  A typical value is 12uS.  I ran into the same problem using
some external muxes and had to increase the sampling time to 20uS.


Harold


Harold Hallikainen
haroldspamKILLspamhallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]

1998\10\28@115859 by Dwayne Reid

flavicon
face
>I'm using a 16C71 to convert 2 analog inputs and then send these
>values out the serial port.  The serial comms are working perfectly -
>my problem is with the a/d conversion.  As the value on one channel
>is adjusted, it affects the other channel, i.e. on the serial output
>I get a change in value on both channels as I adjust only one channel
>while keeping the voltage on the second channel constant.
>Is there a time period that I have to wait between conversions?  The
>two inputs that I'm using are RA0 and RA1.

Yes!  You must select the next channel to be converted, wait a certain
minimum time, then start the conversion.  I usually wait around 60 - 80 uSec
on my '71 and '73 designs.

dwayne


Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(403) 489-3199 voice     (403) 487-6397 fax

1998\10\29@035430 by g.daniel.invent.design

flavicon
face
Peter Howells wrote:
> my problem is with the a/d conversion.  As the value on one channel
> is adjusted, it affects the other channel

1) try to stay in sub 10k range for each chanel's resistance
2) add a small capacitor to each input if possible; the rapid channel
sampling rotation redistributes strongest signals through internal ADC
capacitance.

regards,
Graham Daniel.

More... (looser matching)
- Last day of these posts
- In 1998 , 1999 only
- Today
- New search...