MPXA4115A picbasic code

[iw2fvo]

Good day to all,
I am searching for a reference picbasic code to get pressure from a Motorola MPXA4115A absolute pressure sensor.
Did someone write such a code ?
thanks
Ambrogio

Edit from Moderator:
A Wiki has been created from some of the posts in this thread. It is located here: http://www.picbasic.co.uk/forum/cont...-picbasic-code

[ScaleRobotics]

Darrel has the basic formula here: http://www.picbasic.co.uk/forum/showthread.php?t=182

[Darrel Taylor]

It's been a few years since that thread. Don't even remember doing it.

However, I think pt3rg asked the wrong question back then.
I'm sure he also wanted to convert the A/D reading from the sensor to a pressure value.
May be why he never came back.

With the formula for Vout ...
Vout = Vs*(0.009*P - 0.095)

For 10-bit A/D and 1 decimal, the reverse would be
P = ADC * 0.1086 + 10.6

-- OR --

ADCIN 0, ADval
P = ADval * 1086
P = DIV32 1000
P = P + 106

LCDOUT "P=",DEC P/10,".",DEC P//10,"kPa"

hth,

[Darrel Taylor]

In case you didn't want 10-bit A/D with 1 decimal place in kPa ...

This should cover the other possibilities.
http://www.pbpgroup.com/Calculators/...A/MPX4115A.htm
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[iw2fvo]

Thanks Darrel for your very professional reply on the matter.
I saw your last post just now.
I think your assistance is great for all people in the forum.
Regards,
Ambrogio
IW2FVO
North Italy

[iw2fvo]

Hi Mr. Taylor,

I am goping to prepare an home made weather station : this will be an hobby project for my small radio ham station.
I have seen the pressure transducer calculator you have post to me: it is very interesting.
I would like to use the PIC 10 Bit ADC instead of using an additional 12 bit ADC.
I have considered that my home is at about 1050 ft above the mean sea level and the baro pressure will never change so widely. I have in mind to put the PIC ADC " -REF " to 3.75 Vdc and the ADC " +REF" to 5Vdc.
The 3.75 Vdc is about 938 mB of presssure that has never been observed here in the years.
In this case I will use 10 bit to read the voltage output from 3.75Vdc to 5Vdc.
What do you think about that ? Do you recomand this solution ?
If it will be Ok, what will be the final PICbasic code ?
Thanks a lot for the interest.
Regards,
Ambrogio
IW2FVO
North Italy

[dhouston]

I'll let Darrel help with the coding but, if you haven't used this sensor, you should be aware that decoupling its voltage supply line is critical (Figure 3 in the datasheet). Otherwise, it will be too noisy to make use of its output.

[iw2fvo]

Thanks,
any suggestion for a practical good decoupling of the power supply based on your experience ?
Thanks
Ambrogio

[dhouston]

I used the 1.0µF and 0.01µF as well as the 470pF capacitor values shown in Figure 3 (Page 5) of the datasheet and the output was clean. Before adding them the output was wildly erratic. In my case, I used SMD ceramic caps.

[Darrel Taylor]

I have in mind to put the PIC ADC " -REF " to 3.75 Vdc and the ADC " +REF" to 5Vdc.

The maximum VREF- is (VREF+ -2.0V). So with VREF+ at 5V, VREF- can be 3.0V MAX.

I'll add the option to the calculator later tonight and see what happens.
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[iw2fvo]

Thanks Darrel,
I forgot the vref- constrain. So the VREF- will be 3Vdc.
Ambrogio

[Darrel Taylor]

You're welcome Ambrogio,

I've added the Vref+/- to the calculator.
It should come up with a good formula for you now.

I haven't figured out how to deal with the +/-1.8% error yet.
So these numbers represent an "Ideal" sensor.

MPX4115A Calculator
http://www.pbpgroup.com/Calculators/...A/MPX4115A.htm

Now I gotta go back and redo the MPX4250D for Walter.

hth,

[Acetronics2]

Hi, Darrel

Handy tool, indeed !

Could you add ( or allow ) the 4.096, 2.56, 2.048 and 1.024v "Classical" Vref values ( 3 decimals !!! ) ???

Alain

[flotulopex]

Hi Darrel,

I'm a little confused about how to convert the ADC "pressure" result in an altitude (from 0.2V...4.8V to n meters or feets).

I've read lots of posts, but it is still unclear to me

[Darrel Taylor]

Hi Roger,

Me too.
All I did was convert to kPa, PSI or BAR as shown in this calculator.
http://www.pbpgroup.com/Calculators/...A/MPX4115A.htm

Walter did a project for an altimeter using a lookup table ...
http://www.picbasic.co.uk/forum/cont...-picbasic-code


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