Altitude Accuracy

[Admin]

Our MPL 3115A2 have arrived
Will install next week
Can I get on and wire up without a updated operating system?
dave T

Yes the current version will simply ignore the hardware, the new version which I can give you early access
will configure and use this in preference to the manual value in the web interface

Thx
Lee

[DavidB]

Just to muddy the waters a little more wrt altitude accuracy, although these I2C sensors are very accurate, in a light aircraft with an enclosed cockpit the sensor will be indicating cabin pressure. This could be quite different to static pressure. Totally useless in a pressurised cabin of course.

[Etheav8r]

Corrected SOP diagram with 5v connections to the Adafruit MPL3115A2.

EDIT: Added it as described in my diagram and on the new software build it indicates it is working 

Sorry if this is a stupid question, but just to check (as I know nothing), your diagram and text indicate that the power supplied to the MPL3115A2 is 5v, but the device specs seem to state a max of 3.6v and the units I have, have 3.3v printed against the power pin 2.  Is it safe to get the 3.3v from the RPi IDC pin 1 or should it be taken from the Digole (and from where?)

[trapdoor]

Ian is using a different module.

There are two. One (hobbytronics type - http://www.hobbytronics.co.uk/mpl3115a2-pressure-temp-sensor ) is 3v3 supply. The type that Ian has used which is the Adafruit one (  https://shop.pimoroni.com/products/adafruit-mpl3115a2-i2c-barometric-pressure-altitude-temperature-sensor ) is 5V supply but also has a (weedy) voltage regulator on board that can supply 3v3 - your choice as they both do the same thing but my preference is for the hobbytronics one as there really is no need when using the SoP board to use 5V and the regulator is superfluous.

The Baro module is very low power so you can use the 3v3 supply directly off the RPi without issue - or take it off the Digole if that's what you are using (sorry, thought you were using the SoP board).

[Etheav8r]

Thank you for such a clear and speedy answer.

[rasputin2068]

Lee

MPL 3115A2 added and seen in the web interface, status changes to on when go flying is selected.
When will the next update of the software be issued?

regards

Steve

[Admin]

Just to muddy the waters a little more wrt altitude accuracy, although these I2C sensors are very accurate, in a light aircraft with an enclosed cockpit the sensor will be indicating cabin pressure. This could be quite different to static pressure. Totally useless in a pressurised cabin of course.

Aaahhh yes, I was wondering when somebody was going to notice that one
(apologies to Capt. Mainwaring)

Yes clearly you are right.

I think in this instance, there are only two potential solutions
1. PilotAware needs to be outside the pressurized cabin.
2. The BMP sensor needs to be overriden and use GNSS with a dialled in QNH
this is already supported through the web interface, except when the system recognizes
a BMP sensor, it ignores the dialled in pressure 

seems like the dialled in pressure needs an 'auto' select capability

[Robski]

For those of us lucky to have our own Permit to Fly aircraft who can legitimately tinker with the aircraft systems...

Would putting the barometric board in a separate, sealed box that we then attach into the aircraft's static source be the proper solution?
With this in mind is there a maximum length for the lines between the barometer board in its 'sealed' box and the GPIO / Slice of Pi etc.

[ianfallon]

In an ordinary light aircraft will it really make that much difference ?

I doubt we'll see many pressurised aircraft with PAs - if you have one it will probably have full ADS-B in/out + Mode S already or if not, soon.

[the_top_pilot]

Hello Lee,

I have sourced the baro sensor could you please point me in the direction of wiring diagrams and implementation of the baro unit?

Many thanks

Steve

Hi All,

OK, Solution implemented for this issue, I now have a version of PilotAware with a Barometric Pressure Sensor fitted, and just completed the software/kernel modifications.

So height from PilotAware -> ADS-B traffic will use the Pressure altitude based upon 1013.25mb. This can either be calculated by the use of the builtin Barometric Pressure Sensor, or if no pressure sensor is available, it will use the QNH value (entered through the web interface) to calculate the Pressure Altitude based upon the QNH/GNSS

Height calculations from PilotAware -> PilotAware is always done using GNSS

Pressure sensor used is this one


Thx
Lee

[ianfallon]

It's pretty simple.

If you have the 3.3v baro sensor as described by Lee:

3.3v -> Baro Vin
GND -> Baro GND
GPIO SDA (pin 3) -> Baro SDA
GPIO SCL (pin 5) -> Baro SCL

If you have the 5v Adafruit baro sensor (as I used):

5v -> Baro Vin
GND -> Baro GND
GPIO SDA (pin 3) -> Baro SDA
GPIO SCL (pin 5) -> Baro SCL

Note that the Adafruit baro has a Vo (3.3v output), not to be confused with the 5v Vin !

[Russ_H]

Re: pressure sensor, I have fitted the 3.3v unit, bu tit's not being picked up.
Apart from the physicl connections is there anything else that needs doin? (I am using the 3.3v from the GP10 Connector (Pin 1), is this ok?)

Software is 200151003, though for some reason in the config it shows as 20151005 which I presume is just a typo?

[ianfallon]

First get everything running inc SkyDemon or similar end to end, then check the config at 192.168.1.1 - it might be ok

If not I'd take the 3.3v from your ARF 3.3v supply and check with multimeter

[Russ_H]

Cheers Ian, I have checked it and it is definately not being picked up, I'll try your suggestion of the using the 3.3 from my regulator.

[Admin]

Cheers Ian, I have checked it and it is definately not being picked up, I'll try your suggestion of the using the 3.3 from my regulator.

Hi Russ,
You say it is not picked up, is this because you are looking in the web interface ?
Try connecting your Nav device to PAW first, then refer back to the web interface.
I think until the BMP device is read (as a request from the NAV device) it does not update the web interface

Thx
Lee