MPXA4115A picbasic code

[Darrel Taylor]

The MPX4115A is a "Ratiometric" type of device. Which means that the output voltage is proportional to the power supply voltage.
This is a great feature when using a PIC, because the PIC's A/D converter is also "Ratiometric".
This way you will always get the same results from the sensor, even if your power supply isn't exactly 5.00V or if it drifts a little, like will happen with a battery operated device.

If you try to measure a ratiometric device using a fixed voltage reference ... as the VDD voltage changes, your pressure reading will change too. So you've lost that nice stable signal that a ratiometric sensor gives you.

I don't think you should use a VREF+ at all.<hr>

Using Darrel code for 14bit convertion I have problems with servo in / out routine. Using pulsin/pulsout to re-generate servo signals although normal servo response ok (a little bit jerky motion) when it comes to use Speed controller to ontrol brushless motor it does not seem to respond at all. If I disable Darrel convertion routine SC workink ok.

Trying to do all that in software ... no doubt there are problems.

For 14-bit resolution it takes a minimum of 7.4ms to grab the 256 samples needed.
If you left PBP's default AD defines intact, it could take up to 25ms.
Obviously not fast enough to do software timed servos too.

I agree, an external A/D with higher resolution will probably be best. (without fixed Vref+)

Added:

But if you're just going to a 12-bit external A/D.
You might try the same routines again at the 12-bit resolution. Or even 13-bit.

At 12-bit resolution it only needs 16 samples, which takes <strike>387us</strike> 465us minimum.
Plenty of time left for eveything else.
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