Multiplexing an A/D convertor

D

Dennis Dunn

Guest
Hello,

I would like to connect 1 of n sensors to an A/D convertor. The idea is
to have a microcontroller select one of the n sensors and then have the
A/D do it's thing and then move onto the next sensor. The thing that I'm
not sure of ... rather make that "one of the things" ... is how do I
switch the input of the A/D chip to the ouput of the various sensors?

If the sensors provided digital signals it would be a simple matter but
the output of the sensors are voltages that vary from 0V to 5V. The two
devices I am using are an absolute barometric pressure sensor and an
accelerometer, in the future I would like to add two more accelerometers.

I would appreciate any clues as to what I need to look into next.

Thanks for your time.

--dennis
 
Subject: Multiplexing an A/D convertor
From: Dennis Dunn dennis.dunn@acm.org
Date: 4/13/2004 7:54 PM Central Standard Time
Message-id: <AZ%ec.8400$B%4.5898@fe2.columbus.rr.com

Hello,

I would like to connect 1 of n sensors to an A/D convertor. The idea is
to have a microcontroller select one of the n sensors and then have the
A/D do it's thing and then move onto the next sensor. The thing that I'm
not sure of ... rather make that "one of the things" ... is how do I
switch the input of the A/D chip to the ouput of the various sensors?

If the sensors provided digital signals it would be a simple matter but
the output of the sensors are voltages that vary from 0V to 5V. The two
devices I am using are an absolute barometric pressure sensor and an
accelerometer, in the future I would like to add two more accelerometers.

I would appreciate any clues as to what I need to look into next.

Thanks for your time.

--dennis
Click to expand...
Look into the 4066 CMOS quad analog switch. It gives you four bilateral
switches, and you can set it up quite easily so it will switch one of the four
sensors to your A to D input (view in fixed font, or M$ Notepad):

Analog Multiplexing With a 4066
.-------.
| |
Ain(1)o---------o 4066 o-------o-------------o uC A-D Input
| | |
| | |
'---o---' |
| |
'-----------|-------------o Sel 1
.-------. |
| | |
Ain(2)o---------o 4066 o-------o
| | |
| | |
'---o---' |
| |
'-----------|-------------o Sel 2
.-------. |
| | |
Ain(3)o---------o 4066 o-------o
| | |
| | |
'---o---' |
|-----------|-------------o Sel 3
.-------. |
| | |
Ain(4)o---------o 4066 o-------'
| |
| |
'---o---'
|
'-------------------------o Sel 4



created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

This setup's a bit of an I/O hog, because you need 4 uC pins to select one of
the four switches, but you can do it with one chip. There are other ICs that
will do the job, too. Some have 1-of-n decoders built in, and other features.
Look around -- you'll be amazed how many different ways there are to skin this
particular cat.

http://www.onsemi.com/pub/Collateral/MC14066B-D.PDF

Good luck
Chris
 
CFoley1064 wrote:
Subject: Multiplexing an A/D convertor
From: Dennis Dunn dennis.dunn@acm.org
Date: 4/13/2004 7:54 PM Central Standard Time
Message-id: <AZ%ec.8400$B%4.5898@fe2.columbus.rr.com

Hello,

I would like to connect 1 of n sensors to an A/D convertor. The idea
is to have a microcontroller select one of the n sensors and then
have the A/D do it's thing and then move onto the next sensor. The
thing that I'm not sure of ... rather make that "one of the things"
... is how do I switch the input of the A/D chip to the ouput of the
various sensors?

If the sensors provided digital signals it would be a simple matter
but the output of the sensors are voltages that vary from 0V to 5V.
The two devices I am using are an absolute barometric pressure
sensor and an accelerometer, in the future I would like to add two
more accelerometers.

I would appreciate any clues as to what I need to look into next.

Thanks for your time.

--dennis

Look into the 4066 CMOS quad analog switch. It gives you four
bilateral switches, and you can set it up quite easily so it will
switch one of the four sensors to your A to D input (view in fixed
font, or M$ Notepad):


This setup's a bit of an I/O hog, because you need 4 uC pins to
select one of the four switches, but you can do it with one chip.
There are other ICs that will do the job, too. Some have 1-of-n
decoders built in, and other features. Look around -- you'll be
amazed how many different ways there are to skin this particular cat.
Click to expand...
Thats correct, so why not suggest the analogue multiplexer right of the
bat, say the 4051?

Kevin Aylward
salesEXTRACT@anasoft.co.uk
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
 
Dennis Dunn wrote:
Hello,

I would like to connect 1 of n sensors to an A/D convertor. The idea is
to have a microcontroller select one of the n sensors and then have the
A/D do it's thing and then move onto the next sensor. The thing that I'm
not sure of ... rather make that "one of the things" ... is how do I
switch the input of the A/D chip to the ouput of the various sensors?

If the sensors provided digital signals it would be a simple matter but
the output of the sensors are voltages that vary from 0V to 5V. The two
devices I am using are an absolute barometric pressure sensor and an
accelerometer, in the future I would like to add two more accelerometers.
Click to expand...
If you want to use one ADC with four sensors why not use a four (or
more) channel ADC. There are lots of these available from the usual ADC
manufacturers:

www.analog.com

www.maxim-ic.com

www.ti.com

www.linear.com

You can also get microcontrollers with multichannel ADCs built in,
though possibly not the one you want to use.

Gareth

--
-----------------------------------------------------------------------
To reply to me directly:

Replace privacy.net with: totalise DOT co DOT uk and replace me with
gareth.harris
 
"Kevin Aylward" <kevindotaylwardEXTRACT@anasoft.co.uk> wrote in message
news:TO4fc.6$GW5.1@newsfe1-win...
CFoley1064 wrote:
Subject: Multiplexing an A/D convertor
From: Dennis Dunn dennis.dunn@acm.org
....
I would like to connect 1 of n sensors to an A/D convertor.
....
Look into the 4066 CMOS quad analog switch.
....
Thats correct, so why not suggest the analogue multiplexer right of the
bat, say the 4051?

Probably the same reason I didn't - we were waiting for somebody who
Click to expand...
remembered the part number to chime in. :)

Cheers!
Rich
 
Hello again!

Thanks for all of your suggestions, next stop is the Digi-Key catalog!
I didn't know there was such a thing as a quad-analog switch although it
doesn't surprise me. This is the 21st century, after all. :)

I was going to start learning about uC programming using Microchips PIC
starter kit. I figured that $40 was a cheap investment to help ensure
success in the beginning. Do you have any comments or suggestions?

Thanks again.

--dennis
 
On Thu, 15 Apr 2004 00:30:59 GMT, Dennis Dunn <dennis.dunn@acm.org> wrote:

Hello again!

Thanks for all of your suggestions, next stop is the Digi-Key catalog! I
didn't know there was such a thing as a quad-analog switch although it
doesn't surprise me. This is the 21st century, after all. :)

I was going to start learning about uC programming using Microchips PIC
starter kit. I figured that $40 was a cheap investment to help ensure
success in the beginning. Do you have any comments or suggestions?

Thanks again.

--dennis
Click to expand...
I use the 4051. With 3 digital lines you can select 8 analog channels.
going into a CS5501 type 16bit ADC .
Downside, you have to let the port settle between reads but that may be
true for multi channel ADCs too.


--
Using M2, Opera's revolutionary e-mail client: http://www.opera.com/m2/
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top