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Jul 18, 2013, 10:30 AM
A different attitude to RC
extremewing's Avatar
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New Product

Bluetooth Open Altimeter (BTOA) with G sensor and MS5611 pressure sensor

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Description: Integrated Bluetooth Open Altimeter V1.1

BTOA downloader: The software used to manage a BTOA.
  • Runs on Windows, Mac or Linux
  • Connects using a common micro usb (data/charging) cable or Bluetooth
  • Update the BTOA's firmware to a known working version
  • Modify or view settings
  • Download stored data
  • Displays data on a graph
  • Zoom and analyze data
  • Save or load data from disk
  • and more...
Get the BTOA Downloader V6 for [Windows], [Mac] or [Linux].

To purchase a BTOA please visit the new web site:

NEW: Use the BTOA to drive full color addressable LED strips

The BTOA prompts the Android device running F3K Master to read out your launch altitude as you come in and land nearby or catch the glider. It will also read out the max altitude if applicable and the battery voltage as well as some other information.

Based off the fantastic Open Altimeter V7 ( - thanks Jony and Jan!), this board has:
  • Bluetooth
  • G-sensor (+-24g 3-axis)
  • 8M Memory
  • Built in USB
  • Second voltage monitor input
  • General purpose port (for GPS or anything else you like)
  • The latest pressure sensor (MS5611) which is more sensitive (10cm resolution) and less noisy allowing it to be used as a variometer
  • Download data and change settings over Bluetooth!
  • All functionality of the classic OA
  • Weighing in at 8g
  • A small physical size of 5/8" X 1 7/8" X 3/8".

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The BTOA requires the Downloader app available below for Windows and Mac.

Download and unzip the file for your system.
In the case of Windows, the latest release also includes an installer. For Mac there is a .app file and now also a Linux version.
If you are downloading an earlier version (< 6), run the "Bluetooth Open Altimeter Vxx.jar" file inside the unzipped folder.

For Mac users:
* If your computer does not recognize the USB port it may be necessary to install the USB "VCP drivers" for your OS from here: The port will have a name that includes "tty.usbserial-XXXXX".

* If you get a port error try this:
* If you get a message that the app is damaged, try this: - OR this:
(In summary, right click or control + click the app and select "open") This allows the unsigned app to run.

Connecting the downloader over Bluetooth:
This version of the downloader introduces the ability to connect over Bluetooth and download data or set settings. Bind the computer to the device after it starts up and double beeps.
Once bound, use the "tty.BTOA-XXXX-SPP" serial port to connect on a mac or the (usually) largest serial port number under windows.

A note on cables
There are two types of USB cable out there. One is a "charge only" and the other is "data and charge". The BTOA needs a data/charge cable and if you do not get the device to be recognized at all by the Mac/Pc, try another cable!

4.2 Downloader changes:
- Downloader can now connect over Bluetooth to the BTOA
- Added temperature units under View menu
- Added Vario options to Altimeter Settings dialog
- Serial ports dynamically detected on mouse over the Serial Port menu
- Selected serial port will be remembered
- Enhanced "additional" logging features
- Changed term "Alula" mode to "Sensitive" mode
- Increased download timeout to cater for the larger memory on the BTOA

4.2 Firmware changes:
- Added audio vario functionality for paragliding, hang gliding or other sport pilot use
- Audio vario includes configurable sink alarm
- Added switch action to "reset bluetooth" enabling the downloader to connect over bluetooth after the device has been used
- "Additional" log defaults to vario

30 July 2013 - V4.3 update:
- Changed the BT authentication mode to help with connection problems experienced on some Android's
- Increased connection wait time from 16 to 20 seconds to cater for some Android systems with a longer timeout

1 August 2013 - V4.4 update:
- Possible fix for connection problems!
- Faster connection with less wait time
- The usual startup tone is used instead of the double beep to indicate ready for connection
- Some other changes to how it behaves?

16 December 2013 - V4.5 update:
- Possible fix for verifying settings error
- Possible fix for low voltage alarm trigger being too sensitive
- This version seems to work well, please confirm if you agree?

8 January 2014 - V4.6 update:
This version brings a fix for incorrect power settings with the newer RN-42 V6.15 bluetooth modules that resulted in the device using a lower than expected power output. This affected the connection speed on landing, making the device connect quite late. I also tweaked some window timings to make the connection even faster but this may make it harder to connect initially (try several times if necessary and let me know how it works for you).

15 March 2014 :
4.7 Downloader changes:
- Changed Vario units from feet/min to feet/sec. Old data will have incorrect scales.
- Fixed firmware version check on connect to stop incorrect firmware upgrade required message.
- Changed altitude calculation so the graph should more closely match what was called out on F3K Master. Existing and saved data will now display correctly.

4.7 Firmware changes:
- Changed vario logging to be in feet/sec instead of feet/min.
- Fixed climb rate calculations (was recording approximately half actual rate)

29 April 2014 :

4.8 Firmware changes:
- Fixed formula used for height calculation, removing temperature compensation that was already done so the graph and on field readouts will now match perfectly.
- Changed some BT parameters to hopefully help with connecting to the BTOA from Windows.
- Added a filter to prevent strange spikes in the altitude data from time to time.

16 July 2014 :

V5.0 BTOA Downloader:
- New: flight times calculated in the DLG analysis with a histogram in the results dialog (thanks to Robert (cyclenut) for contributing to this new feature!).
- Faster connection startup with a BTOA. The app no longer waits 24 seconds but rather monitors actual device startup messages in real time to know when it's ready.
- Added file names to window title when downloading, saving and loading data.
- Improved graph annotations.
- Faster data downloads from the device (doubled baud rate to 115200).
- Better reliability while downloading over Bluetooth.
- Backward compatibility (download your data from most older BTOA versions with “I’m feeling lucky”)

V5.0 BTOA Firmware:
- New radio off alarm (enable by setting “Sink Alarm” in settings to 0 and setting up failsafe on the channel to go below the “switch off” position.
- New: Fast scan for faster start time when large log memory is in use. We no longer scan all memory from the beginning to find the first available address but rather break it up into blocks.
- Added: “Log time remaining” (in hours) to BTOA output. (Read out with new F3K Master version to be published soon)
- Added: Calculated flight time to BTOA output. (Read out with new F3K Master version to be published soon)
- Added: BTOA triggers launch on F3K Master with launch g's
- Adjusted power settings and added the 16db high power level for the newer Bluetooth modules that are on BTOA’s.
- Automatically sets new 115200 baud rate on RN-42 on first run.
- Various other improvements and changes.

3 February 2015

I am proud to introduce V0.6.04 of the BTOA Downloader and firmware.

A lot of work has gone into it and the highlights of the new version are a new Java serial library to make it easier to connect to a BTOA without serial driver installation problems. Also, the downloader now sends a checksum with the data so the downloader can tell if the data is as intended.

BTOA Downloader V6.04 changes
- Added the ability to select from multiple flash images.
- Added the ability to preserve settings and or data on flashing
- Added a CRC check to the data download to ensure it's accurately transmitted.
- Added the ability to wipe settings from the Altimeter menu.
- Added a "live" monitor screen to watch values and state of the BTOA in real time.
- New installer for windows users
- New Linux package (missing firmware flash capability)

BTOA Firmware V6.1 changes:
- Added CRC to data sent to downloader.
- Complete rewrite of pressure sensor driver.
- Faster startup time.
- Complete rewrite of Bluetooth driver.
- Update all settings including Bluetooth transmit power without the BTOA restarting to fully support the new "BTOA Settings" dialog in F3K Master.

Get the BTOA Downloader V6 for [Windows], [Mac] or [Linux].

Previous versions of the downloader are also available for download below:
Last edited by extremewing; May 13, 2015 at 12:14 AM.
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Jul 18, 2013, 10:31 AM
A different attitude to RC
extremewing's Avatar
Thread OP

Using the BTOA

NOTE: In order to reduce risk of interference, the BTOA will turn off bluetooth on a launch detect and turn it back on near the ground. Use the lowest bluetooth power that works for you and range test your radio to verify no interference. You should also position the bluetooth antenna (the opposite side to the connectors) as far away from the plane's receiver antenna(s) as you can.

You do use the device entirely at your own risk!!


This device can be powered from either the USB connection or the receiver's power.
Do not connect USB and receiver power at the same time.
Doing so may result in the receiver's battery being charged unexpectedly.

1) Install F3K Master from Google Play.
2) Power on the device and listen for the startup tone. The blue and green lights will be flashing on the BTOA.
3) From F3K Master, press menu > Bluetooth, and check "Enable bluetooth".
4) Select the BTOA from the list or press "Scan for devices" and select the BTOA when it appears in the list.
- If asked for a passcode, use "1234" or just accept the number displayed
5) On connecting, the BTOA will beep and restart Bluetooth in "auto connect" mode and F3K Master will read out the voltage indicating the device is ready to go.

- After a successful connection, there will be a new "Connect to" menu item to connect the last used device.

Go out and fly!

After initial connection to the BTOA, the device will restart the Bluetooth in "Auto connect" mode. You will see a disconnect message and twenty seconds later the device should connect back to the Android and read out the voltage indicating it is ready for use.

About the LED's:
Green flashing indicates logging is in progress.
Red indicates an error or flash memory full.
Blue flashing indicates Bluetooth is active but not connected.
Solid blue indicates Bluetooth is connected.
Last edited by extremewing; Jan 27, 2015 at 01:46 PM.
Jul 18, 2013, 10:39 AM
A different attitude to RC
extremewing's Avatar
Thread OP

How to get one

Since this device is still in the testing phase, I am hand making them for now, but don't let this deter you from getting one. The build quality is good and you would not tell it's done by hand. Besides, if you have any problems, I would always be pleased to help by fixing it or giving you advice on doing the same or even replacing it if necessary!

So far, they are working well, with some more work being needed to test them on a lot of different Android devices to see if there are any problems with the various Android versions out there. That is where you come in. Help by getting one and sharing your experiences with the group.

If you would like one, please visit
Last edited by extremewing; Sep 13, 2014 at 07:33 PM.
Jul 18, 2013, 10:46 AM
A different attitude to RC
extremewing's Avatar
Thread OP

The design

In the spirit of the original OA, this project is also open source. The board designs are available if you want them. Please just ask till the web site is up and running. In the meantime, here is the schematic.

UPDATE: Since I have had good success with testing, I have attached the current firmware and downloader source for those who are interested. Comments are welcome!

Thank you for all the hard work on the schematic and board John C!

New source code attached for V6.

- Arduino code has been updated for Arduino IDE 1.6
- Downloader now uses JSSC pure java serial library.
- More changes as per the change log in the OP.

See op for details of some changes in 5.0
Last edited by extremewing; Jun 26, 2020 at 12:19 PM.
Jul 18, 2013, 11:18 AM
Registered User
shadow102's Avatar
pm sent, interested in picking one of these up
Jul 20, 2013, 02:36 AM
A different attitude to RC
extremewing's Avatar
Thread OP

New version of firmware and downloader in post one and source code available now

Introducing the ability to use the transmitter three position switch to reset bluetooth to "discoverable" so you can connect the downloader without restarting power on the aircraft. Look for "Reset Bluetooth" as an action in the settings dialog.

Defaults have also been changed to "Do nothing" for the three position switch actions.

Longer time reseting the Bluetooth radio to deal with some Androids connection timeouts that caused the device to fail initial auto reconnect.
Jul 20, 2013, 10:27 AM
Registered User
This is absolutely amazing Adrian!! I will test the new firmware and functions with my android devices.

Thanks for your fabulous work
Jul 20, 2013, 01:39 PM
A different attitude to RC
extremewing's Avatar
Thread OP
Originally Posted by kabelbrand
This is absolutely amazing Adrian!! I will test the new firmware and functions with my android devices.

Thanks for your fabulous work
Markus, just bear in mind this code is for the MS5611 pressure sensor on this new board and will not work with the old BMP085.
Jul 20, 2013, 02:16 PM
Registered User
Originally Posted by extremewing
Markus, just bear in mind this code is for the MS5611 pressure sensor on this new board and will not work with the old BMP085.
Oops, you are right! Sorry, so i have to wait a little bit and just have a look
at the code

Jul 20, 2013, 02:32 PM
A different attitude to RC
extremewing's Avatar
Thread OP
In this code I have broken out the BT module parts into their own class and done some tidying up...
Jul 21, 2013, 01:36 PM
sewing machine thumb
I'm having a bit of trouble with the downloaders.

With the Mac version, I unzip and try to execute, but get this message:

"Bluetooth Open Altimeter V4.1 is damaged and can't be opened. You should move it to the Trash" OS/X is version 10.8.4.

I also tried the Windows version, running Windows 7 in a Parallels virtual machine on a Mac. My Windows installation doesn't know how to open a JAR. I tried installing Java, but that was no help.

Any ideas?
Jul 21, 2013, 04:35 PM
A different attitude to RC
extremewing's Avatar
Thread OP
Frank, on Windows, try looking at this:

For the Mac, this may help since it will not be signed:
Jul 21, 2013, 04:49 PM
sewing machine thumb
Originally Posted by extremewing
For the Mac, this may help since it will not be signed:
That worked. Pretty misleading error message by Apple.

Thanks, AD.
Jul 21, 2013, 04:52 PM
A different attitude to RC
extremewing's Avatar
Thread OP
Great news Frank.
Jul 21, 2013, 05:32 PM
sewing machine thumb
As suggested, I also needed to load the latest VCP drivers, and I also needed to make the "if you get a port error" fix.

To pair my Mac with the BTOA, I had to tell click "passcode options" and "do not use a passcode with this device"

Once paired, I needed to exit/restart the downloader before "tty.BTOA-XXXX-SPP" showed up.

I'm going to go stick it in a DLG now!

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