Digital Calibration

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Olivier

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Nov 21, 2011, 9:27:56 AM11/21/11
to pHduino
Hello everybody, this is my first post here :-)

The PHduino design is nice, simple and very functional.
Congratulations and great thanks to Carlos for sharing it.

I had the pleasure to make a PIC version of the PHduino. It works
great but what would make it even better would be a fully digital
calibration.

My first thought is to replace the 2 trimmers with digital
potentiometers.
Reading the FAQ about software calibration, I'm curious to know what
could be other approaches (even if more complicated, less affordable,
etc...)?

Olivier from France

Carlos Neves

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Nov 21, 2011, 10:33:55 AM11/21/11
to phd...@googlegroups.com
2011/11/21 Olivier <olivier...@googlemail.com>
Hello everybody, this is my first post here :-)

The PHduino design is nice, simple and very functional.
Congratulations and great thanks to Carlos for sharing it.

Thank you. I like the idea of the open science.
 

I had the pleasure to make a PIC version of the PHduino. It works
great but what would make it even better would be a fully digital
calibration.

Me too, Olivier. But, At the beginning of the project, I decided to make it very simple about the hardware and the software.

I have been thinking about the second version. It will be an analytical grade instrument and with auto calibration. But, by know, I think small modifications that could make this version more practical.
 

My first thought is to replace the 2 trimmers with digital
potentiometers.
Reading the FAQ about software calibration, I'm curious to know what
could be other approaches (even if more complicated, less affordable,
etc...)?

I need to think about it.
 

Olivier from France


Carlos A. Neves



 

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Olivier

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Nov 22, 2011, 2:48:39 PM11/22/11
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Hi Carlos,

The quad digipots (10k) you are suggesting would perfectly do the job
for lcd contrast and offset adjust but how would you handle the
replacement of the 1M trimpot?
I guess this could ne done by sligthly modifying the overall
schematics but I dont have a good knowledge of analog electronics.
Otherwise we could just serialize 10 100k digipots... that would
require 3 quad ics... unelegant solution...lol :-)


On Nov 21, 3:33 pm, Carlos Neves <cane...@gmail.com> wrote:
> 2011/11/21 Olivier <olivier.ksi...@googlemail.com>


>
> > Hello everybody, this is my first post here :-)
>
> > The PHduino design is nice, simple and very functional.
> > Congratulations and great thanks to Carlos for sharing it.
>
> Thank you. I like the idea of the open science.
>
>
>
> > I had the pleasure to make a PIC version of the PHduino. It works
> > great but what would make it even better would be a fully digital
> > calibration.
>
> Me too, Olivier. But, At the beginning of the project, I decided to make it
> very simple about the hardware and the software.
>
> I have been thinking about the second version. It will be an analytical
> grade instrument and with auto calibration. But, by know, I think small
> modifications that could make this version more practical.
>
>
>
> > My first thought is to replace the 2 trimmers with digital
> > potentiometers.
>
> It is a good idea. The Microchip has some digital trimpots. We need select
> one.
>
> MCP4451http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en551477
> MCP4452http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en551478
> MCP4431http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en551470
> MCP4432http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en551475

> MCP4631http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en536451


>
> > Reading the FAQ about software calibration, I'm curious to know what
> > could be other approaches (even if more complicated, less affordable,
> > etc...)?
>
> I need to think about it.
>
>
>
> > Olivier from France
>
> Carlos A. Neves
>
>
>
>
>
>
>
>
>
> > --
> > You received this message because you are subscribed to the Google
> > Groups "pHduino" group.
> > To post to this group, send email to phd...@googlegroups.com
> > To unsubscribe from this group, send email to
> > phduino+u...@googlegroups.com
> > For more options, visit this group at

> >http://groups.google.com/group/phduino?hl=enHi

Thomas Deutsch

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Nov 22, 2011, 3:02:26 PM11/22/11
to phd...@googlegroups.com
Well, i was thinking the same. I also want to minimize the analog
components and do more Software-work.
You may know the ph-phidget:
http://www.phidgets.com/products.php?category=6&product_id=1130
I do not know how it is done, yet - but it will be a good starting
point i think.
Now, it is a bit rude to suggest another project on this site, but i
think that everyone will benefit if we could implement a
ph-phidget driver to .net micro Framework.


2011/11/22 Olivier <olivier...@googlemail.com>:

Olivier

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Nov 28, 2011, 5:53:24 AM11/28/11
to pHduino
Hi Thomas,

The pH/ORP Adapter you are mentioning looks very nice indeed.
Looking at the picture it seems to use an LPC661im (http://
www.national.com/mpf/LP/LPC661.html#Overview) as OpAmp.
I suspect it thus has some digipot(s) on the other side of the board
to fine tune gain and probably offset just like we are thinking about
for the PHduino "upgrade" we are discussing.

I still wonder if there are other possible approaches, like using a
very sensible ADC that wouldn't require any OpAmp (thus no offset and
gain calibration) or a fully digitally controllable OpAmp, though I
don't know if such products exist.

Any thoughts/ideas?


On Nov 22, 9:02 pm, Thomas Deutsch <deutsch.tho...@gmail.com> wrote:
> Well, i was thinking the same. I also want to minimize the analog
> components and do more Software-work.
> You may know the ph-phidget:http://www.phidgets.com/products.php?category=6&product_id=1130
> I do not know how it is done, yet - but it will be a good starting
> point i think.
> Now, it is a bit rude to suggest another project on this site, but i
> think that everyone will benefit if we could implement a
> ph-phidget driver to .net micro Framework.
>

> 2011/11/22 Olivier <olivier.ksi...@googlemail.com>:

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