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### Topic: BMP 280 exact Altimeter readings.  (Read 546 times)previous topic - next topic

#### tiger369

##### Sep 13, 2017, 07:26 pm
Hi,

I was just going through this pressure sensor tutorial.

What I want to know is how can I set the exact altimeter in my readings depending upon my different geographical place ? or may be if I am attaching the sensor to my balloon.

#### floresta

#1
##### Sep 13, 2017, 09:38 pm
If you get your answer at StackExchange make sure you let us know (and vice versa).

Don

#### jremington

#2
##### Sep 13, 2017, 10:19 pm
In order to calibrate the BMP280 to give correct relative altitude readings, you need to know the actual altitude at some point. Some other means to determine altitude must be used.

Pressure sensors must be recalibrated very frequently.

#### tiger369

#3
##### Sep 14, 2017, 07:04 am
ya, I did post same question at StackExchange also to get different views on same topic. till now I got following answer from Mr. Jose. This seems quite logical.Will work on it.

The tutorial sample source code has the line:

That 1013.25 value should be the local pressure at sea level in hundreds of Pa. If want to show altitude above ground level, you will need to know that for your location and write your code to calculate the altitude offset.

The sensor can't know location -- it only measures pressure. The AdaFruit library provides the altitude conversion, but being generic, it relies on several assumptions.

#### wwaver

#4
##### Dec 05, 2017, 10:04 pm
I have been playing around with this as I want to have an Altimeter with a HUD inside my skydiving helmet. I started using the Example sketch and out of the box works very well. I then decided to start playing with the idea of setting a Relative ground value either on boot or somehow with a input button.

By taking the current pressure and dividing by 100 I could get the current pressure to correct the altitude to zero. All I care about in skydiving is setting my relative ground level to zero each day or jump or whichever.

I started by playing with a float in the loop.