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.]


  1. Hi Al, thanks a lot for this article. I just want to be sure, please can you confirm, that I want to use the right one pair of connectors. I make a red circle about the connectors.Did I choose them correctly? And is it the left one JP1 (so plus) and the right one is JP3 (minus). Thank you and have a nice day

    1. Jan, That is solder jumper you close to ensure that the module comes on at power on. See the "Solder Jumper" section in this post: I have edited the post with an image which points out what you need to do.

  2. Thanks for was informative and userful.

    Bluetooth speakers