CCS C Software and Maintenance Offers
FAQFAQ   FAQForum Help   FAQOfficial CCS Support   SearchSearch  RegisterRegister 

ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

CCS does not monitor this forum on a regular basis.

Please do not post bug reports on this forum. Send them to support@ccsinfo.com

how to avoid a/d channels affecting one-another ?

 
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion
View previous topic :: View next topic  
Author Message
Darren Logan
Guest







how to avoid a/d channels affecting one-another ?
PostPosted: Sun Jul 13, 2003 3:28 am     Reply with quote

Morning/afternoon/evening (depending on locale!),

PIC = 16F873

I'm reading all 5 channels of A/D but I am finding that different voltages on a channel may affect the results on another channel (by up to 50 bits!).
This is a most hideous situation which must be rectified!!!

I have tried adding filter caps (47nF) to inputs of a/d but this has no effect.

Anyone seen and beat this one, if so i'd like to hear from you!

Thanks in advance.

Regards,
Darren
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515920
R.J.Hamlett
Guest







Re: how to avoid a/d channels affecting one-another ?
PostPosted: Sun Jul 13, 2003 4:38 am     Reply with quote

:=Morning/afternoon/evening (depending on locale!),
:=
:=PIC = 16F873
:=
:=I'm reading all 5 channels of A/D but I am finding that different voltages on a channel may affect the results on another channel (by up to 50 bits!).
:=This is a most hideous situation which must be rectified!!!
:=
:=I have tried adding filter caps (47nF) to inputs of a/d but this has no effect.
:=
:=Anyone seen and beat this one, if so i'd like to hear from you!
:=
:=Thanks in advance.
:=
:=Regards,
:=Darren
The commonest cause of this, is not allowing enough time when switching channels.
The input to the AD converter has an internal capacitance, and if it is sitting looking at a 2v input, and is then switched to another channel with a 0.1v signal, will take time to charge to the new voltage. This time is dependant on the impedance of the sources driving the inputs, and the capacitance of the AD input (and on how 'close' the signal needs to get). If the time allowed is not long enough, then when the reading is taken, the pin may only be (say) 90\% charged to the new level, and the reading will be in error (in the case given, reading 0.29v), The value detected in each case, will depend on the voltage on the previous pin...

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515921
Display posts from previous:   
Post new topic   Reply to topic    CCS Forum Index -> General CCS C Discussion All times are GMT - 6 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group