Wednesday 31 December 2014

BlueFlyVario_USB_v10 released

Almost a year ago I started planning for an audio only vario to complement the original BlueFlyVario. I got a little distracted keeping up with orders of the Bluetooth version and the TTL_GPS (because of Kobo vario revolution). I started planning an audio vario again about six months ago. After settling on features, testing and producing an initial batch I am now very happy to announce a limited release the BlueFlyVario_USB_v10.

Design Philosophy

When designing this new vario I wanted to achieve a few things:

  • Build on the work of the successful Bluetooth model by providing a simple device designed for audio output. The firmware is pretty much the same as the Bluetooth and TTL_GPS models. 
  • Make it smaller. I wanted it to be easily able to fit in a helmet. I think this is the smallest vario available for purchase - it is about the size of a AA battery. 
  • Power with a rechargeable battery. Replacing batteries is a pain, but recharging is something we are really used to with our phone. The vario has a micro-USB connector which is the same as most phones. 
  • Provide a simple interface to alter the hardware settings. I considered having a separate USB-to-TTLSerial converter, but settled on incorporating a FTDI FT230X chip to provide an onboard emulated serial port. This only costs a few extra dollars, and does not take up too much board space (especially since I have now moved to using 4 layer PCB's). 
  • Expose the spare UART and audio interface for hacking. 
Because of all of this it ended up being more than just another audio only vario. The USB interface to change hardware settings and hack-able features makes it much more useful. 

Key Specifications

The BlueFlyVario_USB_v10 key features are:

  • Sensitive MS5611 pressure sensor with 10 cm resolution. 
  • Pleasant sounding audio tones, similar to fully featured varios. 
  • Onboard electromagnetic micro speaker (loudness 95dB). 
  • 250mAh rechargeable LiPo battery with 1.25mm Molex connector. Lasts about 10 to 20 hours depending on audio settings. Fully charge in about an hour. 
  • Onboard FTDI FT230X USB Serial chip. The device appears as a serial port with default drivers on most operating systems.  
  • Mass of about 9g. 
What is in the bag?

You need to do the final assembly yourself. You get the following bits in the bag:
  • The main module. This is 50mm x 12mm. 
  • A small piece of neoprene. This is really important. It must be placed over the pressure sensor if the sensor is exposed to any light. The neoprene allows the air pressure through, but stops the light. Light makes the pressure sensor go crazy.
  • A small 250 mAh battery. This is a single cell LiPo with a 1.25mm Molex connector. 
  • A small piece of blue PVC heatshrink. The simplest of cases is all you need. 


    Assembly should only take about five minutes:
    • Step 1 - Attach the battery. Remove the cover of the double sided tape and stick it to the bottom of the circuit board. See the placement in the image below.
    Battery placement
    • Step 2 - Do a quick test. At this point press the button to turn it on. You should hear a few beeps. The number of lower pitch beeps between the high pitch 2 second beep and short 0.5s beep indicate the battery voltage (6 = full, 1 = almost empty). Press and hold the button for 3s to turn it off.
    • Step 3 - Cover. Place the small piece of neoprene over the pressure sensor then encase the whole device in heatshirk. You will need to open up the heatshink to fit it over the button. Make sure the neoprene is covering every part of the sensor. 
    Neoprene placement
    Heatshrink placement
    • Step 4 - Shrink. Use a hairdryer on hot or a heat gun on very low to shrink the heat shrink. The switch might turn on. After shrinking, carefully slice the heatshink from the top of the switch, then shrink a little again. Test again to make sure the switch is working. 
    After shrinking
    Slice heatshink from top of switch
    A neat little circle
    After shinking again around the switch
    • Step 5 - Charge the battery. Plug in to a phone charger to charge the battery. The red LED will come on, then turn off when fully charged. [Note that as soon as you apply power to the micro-usb port that the device will turn on. This is because of stray current from the FTDI chip into the uart on the micro. Every ten minutes when on charge it will power down (based on the auto off feature), then power back on. The auto-on with recharge was an 'unintended feature' of this design. I might change it in the future with a couple of extra resistors in the design.
    • Step 6 - Alter the hardware settings. Most people will probably want to change the sink alarm from the default -0.2 m/s to something like -2.0 m/s (this stops the annoying sink alarm and reduces power consumption). Visit the support page of the website to download the BFV desktop app and the hardware settings manual to understand how to do it. 
    Advanced Use

    There should be a whole bunch of other things that this vario will do for advanced users. The pressure stream coming from the vario means that if you want to use it with an external application like XCSoar then it should be possible, provided the FTDI device enumerates properly on the device. This is only possible on Android/Kobo with some software hacking which I have not done yet. I have not tested this yet on anything other than the desktop version of XCSoar

    At some point I will update the BlueFlyVario Android app to allow the device to be used with a USB OTG connector.


    Like always; I share the design. Intrepid hackers might attach a GPS to the exposed U1 UART port or an external speaker. SJ1 and SJ2 provide for different power options. See the images below.