Air Pressure Sensor for Kite

Humanoido

Using Parallax parts, is there a low cost simple way
to make digital air pressure sensors for flying on kites?
I don't recall anyone making a sensor for the Basic Stamp, or see
any links. If you know atmospheric air pressure, altitude can
be roughly determined, which is the objective.

humanoido

dre

Would this link help?

http://www.rocket-roar.com/rap/alt.html

cheers, David

sylvie369

There are quite a few options for barometric pressure sensors with the appropriate range, but precision may be an issue. Here is a nice little $11 sensor that detects from 15 to 115 kPa (2.2 lbs/in sq to 16.7 lbs/in sq)

http://www.freescale.com/files/sensors/doc/data_sheet/MPX4115A.pdf

and a site that will give you a quick reference for how pressure corresponds to altitude:

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

It'd be nice to have one whose entire range covered just the lower altitudes, though the last time I flew an barometric altimeter it did go to 94,000 feet (in a balloon), which would have maxed out that 4115 sensor. We flew a Honeywell ASDX015A24R, which is a bit pricier ($32) but can measure right down to a nearly pure vacuum.

Anyway, they put out a nice linear voltage over all the altitude and temperature range you're likely to need. However, the +/-1.5% looks like it translates to a couple of hundred feet of error at sea level, which would be a real problem.
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Ken Gracey

humanoido!

Got the solution for you. Parallax is in the final stages of a small module based upon the http://www.vti.fi/en/products/pressure-sensors/pressure_sensors/ SCP1000 pressure sensor: sold by the manufacturer as the most precise pressure sensor in the world! The version we have designed into a module is functional from 0 to 120 kPA (you can figure out the elevation).

Today Josh is doing the final code testing and we are sending it to production next week. I could send you one of the prototypes to try out. Being that you live in a high-rise building, you can easily test it from ground level to the 20th floor. Send me an e-mail to remind me and I'll take care of the request next week.

Sincerely,

Ken Gracey

Humanoido

@ dre
Thank you for the link. This method determines rocket altitude based on accelerometer and time readings. If you have a constant rate of acceleration over time, this equates into distance. An interesting novel approach, but it does not work on kites, which are slow to reach altitude - the rate of climb is not constant or significant enough to register on the accelerometer.

@ sylvie369
Thank you for the links. The chart with air pressure versus altitude is especially helpful. The sensor looks like a good one, for thousand foot altitudes and above. Accuracy is a consideration. Ken has come up with exactly what I'm looking for - a very good sensor with amazing accuracy that looks perfect for the application. Your near space balloon project sounds very exciting. Do you have a web site? It would be interesting and useful to see Earth/Space photos at 94,000 feet!

@ Ken
Thanks!!!

sylvie369

Photos of the workshop, launch, and recovery are at

www.tinyurl.com/balloonworkshop

Unfortunately, I don't have the onboard video yet.

Very good news about the Parallax sensor. I was going to spend today searching for more precise sensors, but I guess now I don't have to. Man, this is a good company.

dre

Oops, sent the wrong link. See if this helps:

http://geocities.com/SiliconValley/Orchard/6633/altimeter.html

cheers, David