SparkFun Forums

[Bill.]

Hi,

I have the BME280:
https://www.sparkfun.com/products/13676

I hooked it up to an Arduino Uno and let it run for 24 hours.

The altitude started at 129 meters. 24 hours later, it showed the altitude as 164 meters, a delta of 35 meters in that 24 hour period.

Apparently a storm rolled through our area and that could/would change the temperature and pressure.

From what I have read, the altitude is calculated from the air pressure.

Question:
Assuming that it makes sense for the altitude to change throughout the day, what can I use the altitude measurement for?

Thanks,
Bill

[jremington]

There is a simple relationship between the altitude and the air pressure, but it assumes that you know the sea level air pressure.

The usual way for using a barometer as an altimeter is to frequently calibrate it, using the current air pressure and known altitude to calculate the equivalent sea level value. Then, if you move up or down, the changes in altitude are reasonably accurate.

[Bill.]

Hi jremington,

Question 1: If one has to frequently calibrate things, then am I correct in assuming that I can't use the BME280 to give me my altitude as I drive on a 500 mile trip, unless I can get the altitude and air pressure at every half hour or hour along the way?

Question 2: If the answer to the above is YES, do airline pilots have a fancy way of re-calibrating their instruments during flights?

Thanks,
Bill

[jremington]

1. "Frequently" depends on whether the atmospheric pressure is changing. Sometimes it doesn't, for days on end. You can verify this using your own equipment.

2. Yes. Airports and most weather reports state the local air pressure, corrected to sea level for just that reason.