Friday, 15 May 2015

Updated BlueFlyVario_Bluetooth_v10 Assembly

I released the BlueFlyVario_Bluetooth_v10 about six months ago (see this post). Most pilots have had no trouble with assembly, but there have been a few issues for some and there is always room to improve. This post describes a slightly different mix of parts you will receive and a simplified assembly procedure. Also, I have made a video of the assembly in response to quite a few requests.

What has changed and why?

  • The PCB is now shipped with the heatshrink and neoprene on. This part of the assembly was tricky for some pilots, the heatshrink would get all messed up, or the neoprene would be stuck the wrong way. I previously suggested putting the battery under the heatshink, now I am advocating to put it outside the heatshrink on the underside of the PCB. This idea came from a Red Bull x-alps competition pilot who wanted to be able to change batteries more easily. 
  • The screws and standoffs are now black plastic instead of metal. There are many good things (5g less mass, greater bluetooth antenna range), but I think it just looks cooler. 
  • The hole for the button on the blue translucent prototype case is now laser cut when the sides are made. This is neater and easier than having to drill every one. 

What is in the bag?

The components in the package are:
  • A BlueFlyVario_Bluetooth_v10 module with heatshrink and neoprene on. This has been bench tested.
  • A translucent blue acrylic prototype case. The acrylic is covered in brown paper.
  • Black nylon screws and standoffs for the case; four each of 12mm screws, 6mm screws, 5mm standoffs, and 6mm standoffs. You will need to shorten the 6mm screws by about 0.5mm using a sharp knife.
  • A 600mAh battery with 1.25mm 2 pin molex connector. The battery has some double sided tape on one side.

Follow the instructions in the video. The testing procedure is described in more detail in the post about the initial release (I did not follow it closely in the video). Please contact me if you have any questions or suggestions.


Sunday, 3 May 2015

Using an external speaker

On the version 10 models of the Bluefly there is a header to connect an external speaker. I have not used it much but have received a few questions. Unless you a really into electronics hacking I would not recommend using a different speaker.

Standard layout

The standard speaker on board the version 10 models is one of the following:

These are all 15 ohm to 20 ohm electromagnetic speakers. On the Bluefly the speaker is driven by a square wave switching a transistor. The circuit diagram and pcb layout on each of the model release blog posts shows how it works. 
The Bluefly runs on 3.0V (TTL_GPS) or 3.3V(Bluetooth and USB). When the transistor is 'on' the speaker would consume up to 150 to 220 mA, however when sounding it is driven by a square wave and making a continuous sound only consumes up to 70 mA. The regulator can provide 100 mA so we are near the limit of its performance. 

Using a different speaker

If you want to use a different speaker a 16 ohm (or greater) device rated for 3V should be used. You could connect it directly to the output, but a connection with a potentiometer is probably more appropriate so you can do some manual volume control (let Google be your friend to see how to wire a pot to provide volume control - search "potentiometer speaker volume control"). I can't recommend a particular speaker, other than advising that larger size generally equals greater sound volume. 

It is prudent to disconnect the current speaker or else it will be in parallel to the new one, and therefore decrease the overall resistance of the speakers. It is tricky to remove the surface mount speaker. The simplest thing to do to disconnect it is to cut the trace to the negative speaker terminal. Only two of the four pads are connected. The positive pad is connected directly to Vdd. The negative pad has a trace (either on the top or bottom) which can be cut. See the board layouts on the links above. Cutting the trace is obviously a one way thing, which is why it is only for serious electronics hackers.

[Edit: The image below shows the speaker pin holes on the BlueFlyVario_TTL_GPS_v10(rev2) board, and the location of the track on the underside of the board which leads to the negative terminal that you would need to cut to isolate the existing SMD speaker.]