Op-amp circuit....

F

FrozenOne

Guest
I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
 
FrozenOne wrote:

I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???

Yes. This is not a simple y = ax + b -- is that intentional? If so,
Click to expand...
what relationship do you really want?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
Yes it is intentionally a non-linear relationship. If I can get
something close to the above it would be great since it does not have
to be a perfect match as long as I am close.
 
On 7 Jan 2005 12:43:23 -0800, "FrozenOne" <ZeroKelvin001@msn.com>
wrote:

I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
Yes, provided the input/output relationship is monotonic.

Surf for piece-wise linear curve-fitting.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
if the relationship is monotonic, could you use a ADC, a lookup table
implemented by memory and a DAC for it?
 
FrozenOne wrote:
I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
yeah, but you only gave spot points, a complete piecewise function would be
nicer.
 
On 7 Jan 2005 12:43:23 -0800, "FrozenOne" <ZeroKelvin001@msn.com>
wrote:

I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
See.....

Newsgroups: alt.binaries.schematics.electronic
Subject: Piece-Wise Linear Question (from S.E.D) - PWL-Example.pdf
Message-ID: <pi9ut0hr3v9lvl71nk0ee77jfdseplc5em@4ax.com>

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Fri, 07 Jan 2005 17:32:58 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On 7 Jan 2005 12:43:23 -0800, "FrozenOne" <ZeroKelvin001@msn.com
wrote:

I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???

See.....

Newsgroups: alt.binaries.schematics.electronic
Subject: Piece-Wise Linear Question (from S.E.D) - PWL-Example.pdf
Message-ID: <pi9ut0hr3v9lvl71nk0ee77jfdseplc5em@4ax.com

...Jim Thompson
Click to expand...
What about using r-r opamps and letting some of them saturate to
define inflection points? Of course, that will have the same glitch
problems of most of the ideal-diode circuits.

I've done breakpoints with non-ideal (real) diodes to bend the curves,
with some other diodes for tempco. The knees aren't as sharp, but
there are no transient spikes.

John
 
In article <1105130603.576279.120500@f14g2000cwb.googlegroups.com>,
FrozenOne <ZeroKelvin001@msn.com> wrote:
I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
Many "single supply" op-amps will swing very close to the (-) rail. If you
run the op-amp from +15 to +24 and ground, you can make an op-amp's output
stay at ground until you hit the knee in the transfer curve. A second
op-amp can combine the output of this op-amp with your original signal to
make a transfer function with an abrupt change in gains.

Op-amps like the LM324 come 4 to a package. You can make 3 knees in the
transfer function this way.


--
--
kensmith@rahul.net forging knowledge
 
"FrozenOne" <ZeroKelvin001@msn.com> wrote in message
news:1105130603.576279.120500@f14g2000cwb.googlegroups.com...
I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
Are there only three points or is it a continuum between 11.7 to 12.5?
Second, what is the precision? I see three significant figures, two
significant figures and one significant figure, which is it? Three
significant figures implies an accuracy and precision of 0.1% while one
significant figure can vary by 10%. This makes a big difference in how you
approach the problem and the precision of the resistors and non-linear
network required. There are also temperature and drift issues as well.

One poster mentioned using a microprocessor with ADC's and DAC's. It could
be a simple look up table to develop the relationship. Beyond that, can the
whole problem be done digitally without ever being in the analog, voltage
domain? That may be the best and simplest. In other words, where do the
voltages come from and how are the results used? It might be easier if those
were digital numbers and not voltages from the get go.
 
FrozenOne wrote:
I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7 12. to 5 12.5 to 12

Can this be done with an op-amp circuit???

Okay so to answer some of the questions:

1) The voltage has to be continuous between the points; I am not
just looking for those points 2) Precision has to be close, but not
exact 3) Do not want to implement digital method 4) I am making the
circuit to control the response of an RF attenuator that I am using
to improve on an older system, and as you can see Analog stuff is not
my strong point. The Existing system can change the output by 6dB by
varying the control from 11.7-12.5 volts. These numbers cannot
change. I am attempting to implement a COTS attenuator to do the
same function, but I need to map the existing control voltage to the
COTS attenuator voltages.
Click to expand...
This is almost certainly an exponential transform. Assuming that your
numbers are exact- which I doubt very seriously- the transform
Vout=2.8+0.9*exp(2.9*(Vin-11.7)) will fit with less than 1% error in the
middle, and nearly exactly at endpoints, and this does make some sense
for transforming between PIN diode configurations-loosely. Given your
background, it would be very unwise to attempt this in any other way
than a piecewise function generator, the above expression can/should be
used as the formula for interpolating between your measured reference
points at Vin=11.5, 12, and 12.5V. Obviously, the transform tends to
grow significantly faster in the interval 12<Vin<12.5, so that your
breakpoints must have have a higher density in this region- they will be
unequally spaced IOW. Most people would use a spreadsheet to bang this
thing out in five minutes. You will end up with a mess of components no
matter what you do- making this a perfect case where a PIC with A/D and
DAC (or PWM+LP filter) really proves itself invaluable for saving money,
space, and time- with performance far exceeding an analog approach, like
giving you 256 breakpoints at a minimum, for free.
 
On Sat, 08 Jan 2005 14:43:06 GMT, Fred Bloggs <nospam@nospam.com>
wrote:

Ken Smith wrote:

Many "single supply" op-amps will swing very close to the (-) rail. If you
run the op-amp from +15 to +24 and ground, you can make an op-amp's output
stay at ground until you hit the knee in the transfer curve. A second
op-amp can combine the output of this op-amp with your original signal to
make a transfer function with an abrupt change in gains.

Op-amps like the LM324 come 4 to a package. You can make 3 knees in the
transfer function this way.



Very nice idea.
Click to expand...
Let the record show that I posted it 33 minutes before Ken did! So how
come it wasn't *my* nice idea?

John
 
I read in sci.electronics.design that John Larkin <john@spamless.usa>
wrote (in <d513u0dsgphuk18dd9q7fe63vg90dj4a5s@4ax.com>) about 'Op-amp
circuit....', on Sun, 9 Jan 2005:
Let the record show that I posted it 33 minutes before Ken did! So how
come it wasn't *my* nice idea?
Click to expand...
Have you allowed for the time-zone?(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
 
On Sun, 09 Jan 2005 11:24:59 -0800, John Larkin wrote:

On Sat, 08 Jan 2005 14:43:06 GMT, Fred Bloggs <nospam@nospam.com
wrote:



Ken Smith wrote:

Many "single supply" op-amps will swing very close to the (-) rail. If you
run the op-amp from +15 to +24 and ground, you can make an op-amp's output
stay at ground until you hit the knee in the transfer curve. A second
op-amp can combine the output of this op-amp with your original signal to
make a transfer function with an abrupt change in gains.

Op-amps like the LM324 come 4 to a package. You can make 3 knees in the
transfer function this way.



Very nice idea.

Let the record show that I posted it 33 minutes before Ken did! So how
come it wasn't *my* nice idea?

I think maybe Fred still has you plonked, poor you! ;-)
Click to expand...

Cheers!
Rich
 
"Why aren't I looking at an AVR selection chart?".
Tim Wescott
Click to expand...
It facinates me that folks who would never say
*I aren't* have no trouble saying *aren't I*.
 
On 7 Jan 2005 12:43:23 -0800, "FrozenOne" <ZeroKelvin001@msn.com>
wrote:

I am looking to map voltages from one point to another, in a specific
maner. For example:

11.7 to 3.7
12. to 5
12.5 to 12

Can this be done with an op-amp circuit???
Click to expand...
Fixed up for single +15V supply...

Newsgroups: alt.binaries.schematics.electronic
Subject: Re: OpAmp Circuit (S.E.D) - PWL-Example-SingleSupply.pdf
Message-ID: <6ed3u0d5lmthpkd9h41v0i0nmokvvblr18@4ax.com>

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
JeffM wrote:

"Why aren't I looking at an AVR selection chart?".
Tim Wescott


It facinates me that folks who would never say
*I aren't* have no trouble saying *aren't I*.

OK, why am't I looking at an AVR selection chart?
Click to expand...

Better?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
 
On Sun, 09 Jan 2005 23:01:38 +0000, Jonathan Kirwan wrote:

On 9 Jan 2005 14:38:31 -0800, "JeffM" <jeffm_@email.com> wrote:

It facinates me that folks who would never say
*I aren't* have no trouble saying *aren't I*.

"The use of ain't as a contraction of am not, are not, is not, has not, and have
not has a long history, but ain't has come to be regarded as a mark of
illiteracy and has by now acquired such a stigma that it is beyond any
possibility of rehabilitation. However, it is used by educated speakers, for
example, when they want to strike a jocular or demotic note, as in fixed
expressions like 'Say it ain't so' or 'You ain't just whistling Dixie.'
Click to expand...
t'aint true at all. 'tis fun to play with language. It pissses off
all the illiterates who graduated from public school in the past twenty
years. ;-)

--
Keith
 
On Sun, 09 Jan 2005 16:00:34 -0800, Tim Wescott wrote:

JeffM wrote:

"Why aren't I looking at an AVR selection chart?".
Tim Wescott


It facinates me that folks who would never say
*I aren't* have no trouble saying *aren't I*.

OK, why am't I looking at an AVR selection chart?

Better?
Click to expand...
amn't. ;-)

And, in answer to your rhetorical question, because I didn't even know to
look there? Nobody ever says, "Use an AVR!", always, "Use a PIC!"

Thanks!
Rich
 
On Mon, 10 Jan 2005 04:32:39 +0000 (UTC), kensmith@green.rahul.net
(Ken Smith) wrote:

In article <S6SxYnF$NZ4BFwP+@jmwa.demon.co.uk>,
John Woodgate <noone@yuk.yuk> wrote:
I read in sci.electronics.design that John Larkin <john@spamless.usa
wrote (in <d513u0dsgphuk18dd9q7fe63vg90dj4a5s@4ax.com>) about 'Op-amp
circuit....', on Sun, 9 Jan 2005:
Let the record show that I posted it 33 minutes before Ken did! So how
come it wasn't *my* nice idea?

Have you allowed for the time-zone?(;-)

Or for the time it took to type the message. John may be a touch typest.
Click to expand...

Two fingers, type by sight (gotta see the keys), lots of mistakes.

John




>--
 
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