MPXA4115A picbasic code

[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

[Darrel Taylor]

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

Done.

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

Hit refresh if you already have the page open.

[iw2fvo]

Darrel,
it is a very usefull calculator: thanks again.
I will use a 5Vdc Vref+ and a divide by resistor divider for Vref-. Could it be OK ?
Is there any possibility to compensate for the accuracy error ?
( I am not familiar with those sensors .. ).
Thanks,
regards,
Ambrogio
IW2FVO
North Italy

[Darrel Taylor]

Resistors will work fine.
It's difficult to get exactly 3.0V using standard values, but with a 4.7K and 6.8K divider, you'll get about 2.96V. Use 1% or better resistors.

These pressure sensors are "Ratiometric" which means that their output voltage changes proportionally to the power supply voltage. So using resistors allows the Vref to change with the power supply voltage too, which is a good thing. A voltage reference that does not change with PS differences can cause incorrect readings if VDD is not exactly 5.00V. Many 7805 type regulators will be anywhere from 4.85 to 5.15V

For the accuracy, each sensor will be off by a different amount up to 1.8% of full scale.
You would need to take readings from the sensor being used at both the high and low ends of the range, and compare them against values read by some other device that is known to be calibrated.

The slope and intercept can then be recalculated for the measured values to create a new formula for that specific sensor. The calculations can be done with the PIC, but I wouldn't recommend it. Or you can do the calculation manually and just enter the slope and intercept into the PIC for that specific sensor.