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Dual Altimeter update


Barry K7BWH
 

The last and final bug (ha!) has been ironed out of the Dual Altimeter feature.

We recommend installing the latest pre-compiled binary file, version 0.35, from www.GitHub.com/barry-ha/Griduino from the downloads folder. For instructions, visit PROGRAMMING.md from the docs folder, section “2. How to Install the Griduino Program.”

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You might notice a new small “sync” button along the right-hand side. Press this to automatically adjust the sea-level pressure so the two readings will match. Although the GPS can be off, it’s usually with 30-50 feet of the correct altitude, so the “sync” button makes it easy to get them close. Then use the +/- buttons to dial in a known pressure or altitude. It shows the sea-level pressure in both metric and English units (same pressure, different units) in case your source of weather reports uses one or the other.

Finally, “Welcome!” to a few new subscribers. It’s great to have you here.

 

Barry Hansen K7BWH

griduino@...

Seattle, WA  CN87us

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Ed N7PHY
 

Just loaded version 0.35 using the .uf2 file. No issues for me and everything looks good. On reboot my Barometer elevation was something like -17000 feet so good opportunity to try the Sync feature. It took about 6 presses of the Sync button to get the barometer in line, each press getting me closer and closer. 

I just purposely mis-calibrated the barometer to give me a 150' elevation difference and one press of the sync button brought it right back in line with GPS.

And only 105 days until the June VHF contest. Everything working fine.

Thank you Barry!

Ed N7PHY


On 2/25/2021 4:25:37 PM, Barry K7BWH <griduino@...> wrote:

The last and final bug (ha!) has been ironed out of the Dual Altimeter feature.

We recommend installing the latest pre-compiled binary file, version 0.35, from www.GitHub.com/barry-ha/Griduino from the downloads folder. For instructions, visit PROGRAMMING.md from the docs folder, section “2. How to Install the Griduino Program.”

A picture containing text, monitor, screen, electronics

Description automatically generated

You might notice a new small “sync” button along the right-hand side. Press this to automatically adjust the sea-level pressure so the two readings will match. Although the GPS can be off, it’s usually with 30-50 feet of the correct altitude, so the “sync” button makes it easy to get them close. Then use the +/- buttons to dial in a known pressure or altitude. It shows the sea-level pressure in both metric and English units (same pressure, different units) in case your source of weather reports uses one or the other.

Finally, “Welcome!” to a few new subscribers. It’s great to have you here.

 

Barry Hansen K7BWH

griduino@...

Seattle, WA  CN87us

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Description automatically generated

 

 

 

 


Barry Hansen
 

Ed, thanks for the update!

The details behind your “-17,000 feet” reading don’t really matter, but if you’re interested in the back story and gory technical details, read on.

Everyone upgrading to v0.35 will see a bogus altitude the first time.

The reason is that the altimeter stores its sea level pressure setting in NVR (nonvolatile ram). The previous software version stored a floating point number of hPa (hectoPascals = millbars), typically around 1017 hPa. The new version 0.35 stores the setting in Pascals, typically around 101700 Pa. The number is exactly 100 times larger and is stored in the same place in NVR. So when the new program reads the old value, it sees a very low pressure as if it’s almost in outer space. If “sea level” is in outer space, then the barometer reading has much higher pressure than “sea level” which represents a much lower altitude. In your case, -17,000 feet.

Implementation of the Sync button has been troublesome. I enjoyed many self-inflicted wounds in my feet while building this feature. Ultimately, I settled on looping through small adjustments to sea level pressure until the altitude (computed by BMP388 library) matches the expected number. As it turns out, writing software to adjust it in the wrong direction was one of the more deadly holes in my foot. After that, the loop acquired a breakout clause to ensure it terminates before the sun goes cold. Ed, that’s why you had to press the Sync button several times to bring it into calibration.

By the way, on this Feather M4 Express, we have lots of NVR. The Uno/Duo/Mega boards offered only a small chunk of on-chip NVR storage. The Feather M4 carries a 2 MB flash chip on which we use a real file system supported by SdFat. Each component in Griduino will read/write its own file to manage its settings. There is room for a long breadcrumb trail plus barometer history and more stuff with lots of space left over. If this ever runs out of space, or if we need to transfer files back and forth, we also have a MicroSD card slot under the TFT display.

There you have it. Now if only I could go roving on top of mountains again. I wish I could drive it over Snoqualmie Pass but they forecast several more feet of snow this weekend on top of the existing 127” and avalanche danger.

Barry Hansen K7BWH
barry@...
mobile 425-503-5548
Seattle, WA  CN87us


From: Griduino@groups.io <Griduino@groups.io> On Behalf Of Ed N7PHY
Sent: Friday, February 26, 2021 10:29 AM
To: Griduino@groups.io Integration <griduino@groups.io>
Subject: Re: [Griduino] Dual Altimeter update

 

Just loaded version 0.35 using the .uf2 file. No issues for me and everything looks good. On reboot my Barometer elevation was something like -17000 feet so good opportunity to try the Sync feature. It took about 6 presses of the Sync button to get the barometer in line, each press getting me closer and closer. 

 

I just purposely mis-calibrated the barometer to give me a 150' elevation difference and one press of the sync button brought it right back in line with GPS.

 

And only 105 days until the June VHF contest. Everything working fine.

 

Thank you Barry!

 

Ed N7PHY

 

On 2/25/2021 4:25:37 PM, Barry K7BWH <griduino@...> wrote:

The last and final bug (ha!) has been ironed out of the Dual Altimeter feature.

We recommend installing the latest pre-compiled binary file, version 0.35, from www.GitHub.com/barry-ha/Griduino from the downloads folder. For instructions, visit PROGRAMMING.md from the docs folder, section “2. How to Install the Griduino Program.”

A picture containing text, monitor, screen, electronics

Description automatically generated

You might notice a new small “sync” button along the right-hand side. Press this to automatically adjust the sea-level pressure so the two readings will match. Although the GPS can be off, it’s usually with 30-50 feet of the correct altitude, so the “sync” button makes it easy to get them close. Then use the +/- buttons to dial in a known pressure or altitude. It shows the sea-level pressure in both metric and English units (same pressure, different units) in case your source of weather reports uses one or the other.

Finally, “Welcome!” to a few new subscribers. It’s great to have you here.

 

Barry Hansen K7BWH
griduino@...
Seattle, WA  CN87us

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