Digital Pot
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Posts: 46,084
I am working on a LCD display that has a contrast adjustment. I want to make it
use a digital pot, But I am having trouble finding one that will work. Maybe
someone can help me find one. I am looking for one that:
has a value of 10K
where the stamp controls it ( the stamp will know where the wiper is at all
times, even on power down)
can handle a negative voltage
please help!
Happy Holidays
AJ
[noparse][[/noparse]Non-text portions of this message have been removed]
use a digital pot, But I am having trouble finding one that will work. Maybe
someone can help me find one. I am looking for one that:
has a value of 10K
where the stamp controls it ( the stamp will know where the wiper is at all
times, even on power down)
can handle a negative voltage
please help!
Happy Holidays
AJ
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
resistor.
--- In basicstamps@y..., "Anthony Conti" <aconti@s...> wrote:
> I am working on a LCD display that has a contrast adjustment. I
want to make it use a digital pot, But I am having trouble finding
one that will work. Maybe someone can help me find one. I am looking
for one that:
>
> has a value of 10K
>
> where the stamp controls it ( the stamp will know where the wiper
is at all times, even on power down)
>
> can handle a negative voltage
>
> please help!
>
>
> Happy Holidays
> AJ
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
> You can vary the wiper but, you cannot get a negative voltage on
the
> resistor.
In the Info I have it just has a 10K pot. With one end of the pot to
gnd one end to the neg voltage and the wiper to the display (
contrast ). I am thinking I might be able to replace the pot with a
digital pot. am I right? or do I have to stick with a normal pot?
AJ
> the
> > resistor.
>
In the Info I have it just has a 10K pot. With one end of the pot to
gnd one end to the neg voltage and the wiper to the display (
contrast ). I am thinking I might be able to replace the pot with a
digital pot. am I right? or do I have to stick with a normal pot?
AJ
OOPS forgot this!
CONTRAST
|
|
|
\/
-V ______/\/\/\______
10K |
|
___
_ GND
voltage. On the equipment I used to service they "stole" the negative
voltage from a Max232 chip.
Just like most LCD's once you set the contrast you don't need to worry about
it again. Only when the viewing angle changes should you need to adjust the
contrast.
I have seen some temperature compensation circuits that vary the bias
slightly, but they still have a manual adjustment.
Original Message
> > You can vary the wiper but, you cannot get a negative voltage on
> the
> > resistor.
>
> In the Info I have it just has a 10K pot. With one end of the pot to
> gnd one end to the neg voltage and the wiper to the display (
> contrast ). I am thinking I might be able to replace the pot with a
> digital pot. am I right? or do I have to stick with a normal pot?
some w/ you for other BS2 stuufs.
--- In basicstamps@y..., "Anthony Conti" <aconti@s...> wrote:
> I am working on a LCD display that has a contrast adjustment. I
want to make it use a digital pot, But I am having trouble finding
one that will work. Maybe someone can help me find one. I am looking
for one that:
>
> has a value of 10K
>
> where the stamp controls it ( the stamp will know where the wiper
is at all times, even on power down)
>
> can handle a negative voltage
>
> please help!
>
>
> Happy Holidays
> AJ
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
regulators and put it in common on the ground of the BS2's regulator?
--- In basicstamps@y..., "iamturbo2000" <aconti@s...> wrote:
>
> > > You can vary the wiper but, you cannot get a negative voltage
on
> > the
> > > resistor.
> >
> In the Info I have it just has a 10K pot. With one end of the pot
to
> gnd one end to the neg voltage and the wiper to the display (
> contrast ). I am thinking I might be able to replace the pot with
a
> digital pot. am I right? or do I have to stick with a normal pot?
>
> AJ
>
> OOPS forgot this!
>
>
> CONTRAST
> |
> |
> |
> \/
> -V ______/\/\/\______
> 10K |
> |
> ___
> _ GND
Xicor has a range of digital pots including ones for V+/V-
You find their selection guide at
http://www.xicor.com/product_select_guide.php?table=xdcp
regards peter
Oorspronkelijk bericht
Van: iamturbo2000 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=fbjKmjmh9JqkRPvCBPwslPFSAw7Ar8ISqfnJw4VHQV2e3dCIMN59li0MfdkJgefOtL4PFv0UZECHSA]aconti@s...[/url
Verzonden: maandag 24 december 2001 18:23
Aan: basicstamps@yahoogroups.com
Onderwerp: [noparse][[/noparse]basicstamps] Re: Digital Pot
> > You can vary the wiper but, you cannot get a negative voltage on
> the
> > resistor.
>
In the Info I have it just has a 10K pot. With one end of the pot to
gnd one end to the neg voltage and the wiper to the display (
contrast ). I am thinking I might be able to replace the pot with a
digital pot. am I right? or do I have to stick with a normal pot?
AJ
OOPS forgot this!
CONTRAST
|
|
|
\/
-V ______/\/\/\______
10K |
|
___
_ GND
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> Where did you got the negative supply? You used the 79 series
> regulators and put it in common on the ground of the BS2's
regulator?
I am using part number "LT1054" from Texas Instruments
http://www.ti.com/ . It is a DC/DC conveter
I am not at my office so I cant remember the number but you can get it from
the web site
www.analog.com
Alan Bradford
Plasma Technologies
smartdim@a... writes:
> My maximum pot value calculates about 1500 ohms..
>
> Q1) Has this been done before, good or bad results?
>
> Q2) Initial search on digital pots showed a max values of 50K and
> 100K ohms. I would want a digital pot with a max value of about 5k
> max (2k better). Any ideas?
>
Depends on how much current you are drawing. If you adjust your regulator to
6 volts, assuming about 2500 ohms and are drawing 50ma, that would take a 6
watt resistor! Digital pots are rated at about 1ma on the wiper, I think.
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
voltage of a three terminal voltage regulator (control of 1.25 volts
to 9 volts).
My maximum pot value calculates about 1500 ohms..
Q1) Has this been done before, good or bad results?
Q2) Initial search on digital pots showed a max values of 50K and
100K ohms. I would want a digital pot with a max value of about 5k
max (2k better). Any ideas?
Thanks
resistance of 0 ohms for the 1.25 volt output.
All the digital pots I have looked at have a wiper resistance of 300
or more ohms......dang...
Going to have to go with the analog multiplexor and a resistor
divider network.
--- In basicstamps@yahoogroups.com, "coiltap2003" <smartdim@a...>
wrote:
> I am about to use a stamp and digital pot to control the output
> voltage of a three terminal voltage regulator (control of 1.25
volts
> to 9 volts).
>
> My maximum pot value calculates about 1500 ohms..
>
> Q1) Has this been done before, good or bad results?
>
> Q2) Initial search on digital pots showed a max values of 50K and
> 100K ohms. I would want a digital pot with a max value of about 5k
> max (2k better). Any ideas?
>
> Thanks
digital pot?
The response of the MOSFET will not be linear, but you should be able
to compensate for this through the digital pot.
>Looks like this idea will not work since I will need a minimum
>resistance of 0 ohms for the 1.25 volt output.
>
>
>All the digital pots I have looked at have a wiper resistance of 300
>or more ohms......dang...
>
>Going to have to go with the analog multiplexor and a resistor
>divider network.
>
>
>
>--- In basicstamps@yahoogroups.com, "coiltap2003" <smartdim@a...>
>wrote:
> > I am about to use a stamp and digital pot to control the output
> > voltage of a three terminal voltage regulator (control of 1.25
>volts
> > to 9 volts).
> >
> > My maximum pot value calculates about 1500 ohms..
> >
> > Q1) Has this been done before, good or bad results?
> >
> > Q2) Initial search on digital pots showed a max values of 50K and
> > 100K ohms. I would want a digital pot with a max value of about 5k
> > max (2k better). Any ideas?
> >
> > Thanks
Beau Schwabe Mask Designer II National Semiconductor Corporation
500 Pinnacle Court, Suite 525
Mail Stop GA1
control a power supply. You might find the spreadsheet included of interest.
http://www.catalyst-semiconductor.com/dppstampapplications/
Regards,
Al Williams
AWC
* Control I2C from your PC
http://www.awce.com/gp7.htm
Original Message
From: coiltap2003 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=S31faz3hkaStsnQGIkKqZZfKF7OuurrxovhbWD8JKgVr4IPWAwDmEuE2h1Z6tDpr-CUEINj2Kg]smartdim@a...[/url
Sent: Wednesday, July 21, 2004 2:28 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Digital Pot
I am about to use a stamp and digital pot to control the output voltage of a
three terminal voltage regulator (control of 1.25 volts to 9 volts).
My maximum pot value calculates about 1500 ohms..
Q1) Has this been done before, good or bad results?
Q2) Initial search on digital pots showed a max values of 50K and 100K ohms.
I would want a digital pot with a max value of about 5k max (2k better). Any
ideas?
Thanks
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LM317 variable 3 terminal voltage regulator.
The digital pot is to control the regulator, it is NOT a load.
Ken
--- In basicstamps@yahoogroups.com, Newzed@a... wrote:
> In a message dated 7/21/2004 3:31:27 PM Eastern Daylight Time,
> smartdim@a... writes:
>
>
> > My maximum pot value calculates about 1500 ohms..
> >
> > Q1) Has this been done before, good or bad results?
> >
> > Q2) Initial search on digital pots showed a max values of 50K and
> > 100K ohms. I would want a digital pot with a max value of about
5k
> > max (2k better). Any ideas?
> >
>
> Depends on how much current you are drawing. If you adjust your
regulator to
> 6 volts, assuming about 2500 ohms and are drawing 50ma, that would
take a 6
> watt resistor! Digital pots are rated at about 1ma on the wiper, I
think.
>
> Sid
>
>
> [noparse][[/noparse]Non-text portions of this message have been removed]