Sunday, 20 December 2015

GPS and Airspeed Shields

I was really happy to release the BlueFlyVario_Bluetooth_v11 a few weeks ago. Since then I have found some time to get the GPS and Airspeed shields ready to go. In this post I will describe how the shields work and what you need to do to integrate one to the BlueFlyVario_Bluetooth_v11. A word of warning - the shields are for experienced tinkerers who are good at soldering and want to experiment.

The Shield Concept

I have developed quite a few different BlueFly models over the past few years. It all started with a simple device that just sent pressure data via Bluetooth. In v6 I added audio, a TTL version came later, then with Kobo mods becoming popular we got the TTL_GPS model. Firmware update-able versions started with v10.

If I just kept on adding sensors and other components to the BlueFly we would end up with a device that has a lot of stuff that many people would not use. That would be a waste of time for me, and a waste of money for users. However, there were some key things I wanted to be able to offer experienced users. The micro-controller on the v11 has enough spare pins to allow extra things to be added. Instead of adding sensors on the main BlueFly board I decided to offer extra capacity with an add on shield. The 'shield' is just a small daughter-board the same size as the BlueFly board. This is sandwiched with the BlueFly and connected with headers to make a more powerful device.

The images below shows the circuit diagram and PCB layout of the shield. Note that the components which can be attached to RB10 and RB11 can either be configured as buttons or LED's depending on what is populated.


Description: The B_v11_Shield_GPS adds a PA6H GPS on UART1 (U1) of the microcontroller. The GPS shield has a few extra components to smooth the power supply to the GPS and provide the PA6H LED output. Note that the BlueFly button protrudes through the hole in the shield. The GPS works in exactly the same way as the GPS on the TTL_GPS models of the BlueFly:

  • Any sentences coming from the GPS which begin with $ and ending with new line (\n) are echoed out on U2 by multiplexing the with the standard BlueFly output. 
  • The BlueFly does nothing with the GPS information other than pass it through. 
  • At this stage XCSoar is the only application which reads both the BlueFly output (in a few different modes) and the standard GPS sentences from the same data stream. 
Target Users: I expect that most people that want the v11 Bluefly and this add on v11 GPS shield will be wanting to connect it to a Kobo which as been modified to accept Bluetooth connections. Anyone who intends to use the BlueFly with a device that already has a GPS (like and Android or iOS devices) should not bother with this module.

Released Version: The BlueFly_v11_Shield_GPS is provided in kit form. The kit includes the items pictured below:

  • The BlueFly_v11_Shield_GPS board.
  • Some pins for connection to the BlueFlyVario_Bluetooth_v11 (these will need soldering). 


Description: I have been tinkering with Airspeed for some time. It was not until I started experimenting with the MS4525DO differential pressure sensor that I found something I was happy with. This is the same sensor which is used in the PX4 airspeed sensor and is connected via I2C.

The MS4525DO upper port (the one near the top of the picture) is connected to the pitot pressure and the lower port is connected to the static pressure. The included pitot tube and clear tubing is a cheaply available RC model tube and will need modification at the nose to make it work properly as when it is machined the pitot hole gets a little closed. You will have to tinker with the physical layout of the tube to get it accurate, although note that there is no way to get accurate airspeed below about 10 to 15 km/hr.

Some additional notes (I will update the hardware settings manual at some stage):

  • The BlueFly needs a special hardware setting adjusted. To adjust usePitot send $BUP 1* to the BlueFly via the normal manner (or tick the box in the BFVDesktop application). This makes the BlueFly read this pitot sensor each cycle via I2C and adjust the sent data appropriately. This will be described fully in the manual update; but in the interim note that the LX mode sends the indicated airspeed (IAS) when usePitot is set.
  • When the BlueFly starts up with usePitot enabled it immediately begins a pitot calibration. This lights the red LED on the shield, then takes about five seconds of pitot data. The differential pressure measured is averaged and taken to be zero airspeed. 
  • You can trigger another calibration at any time by pressing the red button on the shield next to where the normal BlueFly button protrudes. It is important that the pitot tube is in no wind when the calibration is underway. 
  • If you set usePitot, but the shield is not connected, the BlueFly will send an error message. 
Target Users: I expect that most people that want the v11 Bluefly and this add on v11 Airspeed shield will be experimenting with different configurations. I am yet to be convinced that there is some logical place to put a pitot tube anywhere on a paraglider which has clean enough air; it is easier on a hangglider. At some stage I will probably design a 3D case to mount the pitot tube and vario components.

Released Version: The BlueFly_v11_Shield_Airspeed is provided in kit form. The kit includes the items pictured below:
  • The BlueFly_v11_Shield_Airspeed board. 
  • A basic pitot tube and clear tubing. 
  • Some pins for connection to the BlueFlyVario_Bluetooth_v11 (these will need soldering). 


Description: This provides the capabilities of both modules in one. See the image below:


To assemble the shield onto the BlueFly requires some skill or a friend who knows what they are doing with a soldering iron. There are many ways it could be assembled together, and in the end you will need some kind of case which houses everything. At some point I will probably design a 3d printable case but so far I have only tested it with a Frankenstein mix of tape and heatshink which will be unacceptable for most people.

Some assembly tips:

  • You will need to disassemble the BlueFly and disconnect the battery. 
  • Start by soldering the pins on to the BlueFly, short ends in the pcb from the component side, then solder from the bottom. You should use all 11 pins (4 on one side, 7 on the other). 
  • Use the 5mm standoffs from the BlueFly to position the shield above the main board. Note the button protruding through the hole at just the right height. 
  • Solder the pins to the shield from the top. 
  • Plug the battery back in (protect it from the pins with some tape), connect to the BFVDesktop application, then start testing. 
See the image below for an indication of what a shield looks like when connected to the base BlueFly.

Next Steps

There is quite a lot more to do:
  • Design a 3d printable case for use with the airspeed sensor.
  • Much more testing with the airspeed sensor. 
  • Integration of GPS and airspeed information with other apps
  • Update the hardware settings manual. 
The shields are available for purchase now. Note that I am only producing them in low volumes and will hand assemble and test each one based on the number of orders received.