Friday 5 November 2021

BlueFlyVario_TTL_GPS_V12.2 released

The BlueFlyVario_Bluetooth_TTL_GPS_v12.2 is ready for release. This model has been developed because the lead time on the XA1110 GPS module is crazy, and all of my stock of that module is reserved for the GPS_IGC model. Nonetheless, from crisis come innovation, and this model has some major benefits over the TTL_GPS_v12 released over three years ago. The number of pilots installing a BlueFly on a Kobo has reduced, but it is still very popular and I am pleased that I have found a way to continue to support it during the chip shortage. 

What is going on with chips? 

The global electronics chip shortage is madness. For a little electronics design and manufacturing company like Bluefly it is particularly bad. I am a one-man part-time business and the chip shortage has affected availability, price, and development.   

  • I can get one or two of almost any component, or if I was a big manufacturer am sure I could get half a million of critical components, but trying to find 500 to 5000 of anything made of silicon is hard. That is exactly the quantities that a company like the Bluefly is operating in. 
  • The price of all components are up 20% to 50%. 
  • All of this makes development harder. Over the last year I have been designing sub-components of a future vario project, using a different pressure sensor and new microcontroller family, but just as I was ready to build a full prototype, lead times for the components I included in the design extended to over a year. This has not been wasted time, but it will postpone my plans. 
The new GPS

There are a few GPS modules that are suitable for these little Blueflys.  I am looking for GPS modules that include an antenna for reduced part count, are surface mount for easily assembly, are small enough to fit in the design. Most importantly, the module must be available in the quantities needed. There are basically two types; those with a ceramic antenna (like the XA1110 of the previous model), and those with a small chip antenna. 

I have experimented with chip antenna in the past, but I could never get the performance to work as well as a ceramic antenna. However, with the TTL_GPS there are some criteria that made me think I could get it to work. I could make the circuit board large enough for a good ground plane, and there was no need for a battery with copper foil directly underneath the antenna. After a bit of research I found the Quectel L96 and decided to experiment with it. This has some advantages of having the same internal MTK chipset I am familiar with and the price is comparable. 

After my first prototype it was pretty clear that this was going to work. In fact, the performance of the ceramic chip antenna for this GPS with a larger ground plane is better than the previous ceramic antenna model (reduced time-to-first-fix). The image below shows the difference in size between the v12.2 (top) at 20mm x 60mm compared to v12 (bottom) at 17mm x 50mm. It is difficult to see, but without the height of the ceramic antenna the new vario has a much lower profile. 

New hardware features

The BlueFlyVario_Bluetooth_TTL_GPS_v12.2 has some differences from the earlier designs:

  • It is larger, as described above.
  • The component layout is different (switch and speaker on the opposite side, sparser components). This is all about designing the board to maximise the performance of the chip antenna. 
  • The headers/pins for the TTL serial connection have solder tabs to offer alternate ways to connect the wires. 
  • I have included a V_Backup tab. For most users I do not suggest that you use this (and do not suggest that you close the solder jumper to connect it to V+). If you feel that V_Backup is for you make sure you read the datasheet for the L96 to understand how it works. 
  • The ON solder jumper next to the voltage regulator is closed by default. This means that as soon as power is connected between GND and V+ that the vario will power on. If you want the same behaviour as the v12 then you can cut the connecting wire on the tab. 
  • The GPS LED is orange. When the GPS has a 3D fix it will flash. 
  • Pads for GND, RST and BOOT are exposed on the top of the board. 
    • Short GND and RST when powering on to reset the default hardware settings. 
    • Short GND and BOOT when powering on to enter the bootloader for updating firmware via TTL_Serial (if I release an update). 
  • Note that there are a couple of components near the GPS that are not populated. This is not a mistake. 
The image below shows the layout on the front and back of the board. 

New firmware

Some updates to the firmware for this model include:
  • Some changed default settings to match the different GPS (internal baud rate).
  • startDelayMS is set at 2000 by default. This adds a 2s delay between the vario powering on (indicated with a very brief chip), and data being sent out. It is used because the ON solder jumper is closed by default. The behaviour is that when your Kobo is started, and power flows from the Kobo serial port, the vario starts right away. 
  • There is a higher performing vario/GPS sentence multiplexing algorithm. 
What is in the bag?

The BlueFlyVario_TTL_GPS_v12.2 includes:
  • The vario module.
  • A small piece of neoprene. It is very important that this is placed over the pressure sensor to protect it from the light, but still allow air to come through. Make sure to leave the white tape on, and place the black squishy side of the neoprene on the sensor. 
  • Some blue PVC heatshrink to hold the neoprene in place and help protect the components. You will only put this on at the final assembly stage. 
  • Some telephone cable. Strip this for the individual wires. 

Simple Assembly

There are many ways to assemble the module on the Kobo. I suggest you read old blog posts on here and check out Nev's page at for more ideas. Some pilots design 3D cases. I prefer a simple install method these days. 

Some important tips for all installs:
  • Keep the wires as short as possible. The location of the Bluefly will depend on which kobo you have. Note that xcsoar can be configured in any of the four orientations and you should select a layout to match. 
  • Put the neoprene on correctly. Make sure the black squishy side is on top of the pressure sensor to protect it from light, but still let air in. 
  • Keep your solder joints clean. Use a hot soldering iron with flux for the minimum time needed to get good solder joints. Clean the flux off with isopropyl alcohol. 
  • Make sure the antenna is hanging over the edge of the bezel, with nothing behind the keep out area on the back of the Bluefly board. 
  • In xcsoar, set the Bluefly as Device A, Port: ttymxc0 (or something like that, only one will work), Baud rate: 115200, Driver: BlueFly Vario.
The image below shows mid way through an install on an old Kobo Glo. Notice the neoprene in the right spot. At about this point I always make sure that I check the Monitor in the Devices menu of xcsoar to see the data streaming in. 

In my simple installs I generally just attached the vario using double sided tape (after heatshrink). Hot melt glue helps protect the wires.