Changing DC level from a sensor

Tue Aug 31, 2010 2:32 am   

I have a sensor whose output varies from +2.5 volts DC to + 4.5volts DC.
I would like to 'shift' this to become 0 - 2volts DC.
Presumably with an op-amp?
Single supply IC preferable e.g. LM358
Appreciate some advice on how to accomplish this.

JERD

Tue Aug 31, 2010 12:46 pm   

On 2010-08-31, JERD <notme_at_bigpond.net.au> wrote:


simple summing network:

.--R--0V
|
in --R-o-+\
| >-o--- out
2.5V -R-o--/ |
| |
`--R--'

dunno how close to 0V that'll go, use larger R if necessary.



--
¡spuɐɥ ou 'ɐꟽ ʞooꞀ

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Tue Aug 31, 2010 12:59 pm   

On Tue, 31 Aug 2010 10:50:26 +0930, JERD wrote:


Put a 2v zener ad a resistor in series across the output and take the
reading off the resistors?

Tue Aug 31, 2010 1:56 pm   

"JERD" <notme_at_bigpond.net.au> wrote in message
news:MNYeo.5026$FH2.2763_at_viwinnwfe02.internal.bigpond.com...

volts with a simple zener is likely to result in a fairly unstable zero
point, as well as some added source resistance you may be better without. If
you want something a bit better you could build a standard diff amp from a
single supply opamp such as the one you suggest. Any opamp cookbook website
will have a schematic.

Tue Aug 31, 2010 11:01 pm   

"JERD" <notme_at_bigpond.net.au> wrote in message
news:MNYeo.5026$FH2.2763_at_viwinnwfe02.internal.bigpond.com...

**Buy yourself a copy of Walt Jung's 'OP Amp Coookbook'. You can work it out
for yourself. Alternatively, you can scan the Natsemi datasheets for some
common OP amps. There will probably be an application note suitable for your
needs.


--
Trevor Wilson
www.rageaudio.com.au

Wed Sep 01, 2010 12:45 am   

JERD wrote:


Does it have to go down to zero?, if not, a resistor divider could work
fine.

Wed Sep 01, 2010 1:55 am   

"Mark Harriss" <billy_at_blartco.co.uk> wrote in message
news:WaidnX_eQOlXDuDRnZ2dnUVZ8s2dnZ2d_at_westnet.com.au...

Thanks for all replies of assistance.

My preference is for it to go to zero.

I am going to have a try of all of the suggestions and increase my knowledge
at the same time. At age 68 the brain doesn't work as well as I would like
these days!

JERD