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'Barometer using PIC, ADC0831, MPX5100A sensor'
1996\11\09@184339 by Roland Andrag

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Hello!

{Quote hidden}

I beg to differ here - although the differential (guage) models like
the MPX5100D support a differential pressure of 100 kPa, the absolute
pressure sensors (MPX5100A) use an internal reference that sits at
about 15 kPa.  The absolute range measurable with the MPX5100A is
thus also 15 - 115 kPa.

I am in the process of building an altimeter using a PIC and the
MPX5100A sensor, which is very well suited due to the fact that it is
fully temperature compensated. Is there any reason for using an
external A/D converter instead of using something like the PIC16C71
which has a four channel 8-bit A/D built in (besides the '84 EEPROM
vs '71 EPROM)??

Cheers
   Roland

1996\11\10@022916 by Hank Gupton

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Roland Andrag wrote:

>I beg to differ here - although the differential (guage) models like
>the MPX5100D support a differential pressure of 100 kPa, the absolute
>pressure sensors (MPX5100A) use an internal reference that sits at
>about 15 kPa.  The absolute range measurable with the MPX5100A is
>thus also 15 - 115 kPa.

 You would be wise to heed the advice.  A Motorola Data-sheet states that
the MPX5000 series is only useful for the stated range because the
calibrated amplifier hits the rail at the end of the range and no further
change in output will be observed.  Regardless, of what you think _should_
happen.

 What is your objection to the MPX4115A?


>I am in the process of building an altimeter using a PIC and the
>MPX5100A sensor, which is very well suited due to the fact that it is
>fully temperature compensated. Is there any reason for using an
>external A/D converter instead of using something like the PIC16C71

 The external A/D converter is 12-bit; the internal, 8-bit.  It's a
question of granularity.  Do you want your altimeter to register 256
separate Feet (Meters) or 4,096 separate Feet (Meters) of altitude?

 -- Hank

1996\11\11@012628 by Werner Terreblanche

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Roland Andrag <spam_OUTANDRAGTakeThisOuTspamBUDGET.MECH.WITS.AC.ZA>

> I am in the process of building an altimeter using a PIC and the
> MPX5100A sensor, which is very well suited due to the fact that it is
> fully temperature compensated. Is there any reason for using an
> external A/D converter instead of using something like the PIC16C71
> which has a four channel 8-bit A/D built in (besides the '84 EEPROM vs
>'71 EPROM)??


 As someone who is also using the MPX5100A sensor in Variometer
product that I built for Paragliding and Hangliding enthuisiasts, I
feel that that I also ought to say my little bit here...  :)

My vario uses a PIC16C71 with some analog circuitry to condition the
signal before it goes to the the AtoD.  You will find that without this analog
circuitry, the 8 bit A/D of the 16C71 would not provide sufficient
resolution and sensitivity.   However, if you want to use
some higher resolution external A/D's like the MAX195 which is a serial I2C 16
bit A/D, then you can probably do away with any external analog
circuitry and still have exceptional accuracy.    So I agree with
Roland, I would also go for an external A/D, unless cost is a big
issue.

Another popular technique would of course be to use the technique of
converting the analogue signal to a frequency using a voltage to
frequency converter and measuring this frequency.  This is generally
less expensive than external A/D, but with additional problems such
as temperature compensation and measuring range problems.

Regards
Werner

--
Werner Terreblanche   Tel +27 21 7102251   Fax +27 21 721278
.....wterrebKILLspamspam@spam@plessey.co.za (work) OR wernerspamKILLspamaztec.co.za  (home)

1996\11\11@034201 by Chris Cain

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>I am in the process of building an altimeter using a PIC and the
>MPX5100A sensor, which is very well suited due to the fact that it is
>fully temperature compensated. Is there any reason for using an
>external A/D converter instead of using something like the PIC16C71
>which has a four channel 8-bit A/D built in (besides the '84 EEPROM
>vs '71 EPROM)??

it depends on the accuracy you want,
8 bit A/D gives you 256 levels, assuming you want a range of (say) 0-25,000ft
this means the resolution is 100ft, and the accuracy is +- 1lsb = 200ft.
If this is good enough for your requirements then the internal A/D is fine
otherwise you have to do a bit better.

Chris Cain

>
>Cheers
>    Roland
>
>

1996\11\11@103605 by Les Troyer

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According to Roland Andrag:
>
> I beg to differ here - although the differential (guage) models like
> the MPX5100D support a differential pressure of 100 kPa, the absolute
> pressure sensors (MPX5100A) use an internal reference that sits at
> about 15 kPa.  The absolute range measurable with the MPX5100A is
> thus also 15 - 115 kPa.
>
> I am in the process of building an altimeter using a PIC and the
> MPX5100A sensor, which is very well suited due to the fact that it is
> fully temperature compensated. Is there any reason for using an
> external A/D converter instead of using something like the PIC16C71
> which has a four channel 8-bit A/D built in (besides the '84 EEPROM
> vs '71 EPROM)??
>
> Cheers
>     Roland
>

I also have an altimiter in the pipeline.  I chose to go with an external
12bit A/D converter.  The quantiums of the 8 bit were > 40 feet (if i remember
correctly).  I wanted something with less than 2' quantiums.  Other than that
the issue might be size.  The 84 + small serial A/D is less realestate than
the 71

--
Les Troyer
Sr. Analyst
Siemens Power Corp
2101 Horn Rapids Rd.
Richland, Wa. 99352-0130

Voice    (509) 375-8695
Fax      (509) 375-8940
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email .....ljtKILLspamspam.....nfuel.com

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