Friday, 22 November 2013

First stab at adding bluetooth

I had a go at adding Bluetooth support to the turned speaker I made using an RN-52. It wasn't clear from the datasheet what sort of output I could expect from the RN-52.  All it said was that it was differential.  I tried hooking up one side of the differential pair to the headphone-in of the speaker to get a better understanding.  It worked! (Kinda!)

While audio was playing (with about 12 ohms across the input to ground) it was fine but there were very large pops when sounds started and stopped.  I suspect (but I don't have a scope available to check) the module centres its signal on 1/2Vin but turns off the driver when it's not using it.  That results in a big step signal when it turns its signal on and off, causing a pop.

Thanks to a tip from the AskElectronics subreddit, I now plan to build the headphone out circuit from the datasheet and then find some way to mix that with the existing headphone in, if possible.

Monday, 11 November 2013

Turned purpleheart speaker

Turned purpleheart USB-powered speaker

I made this turned speaker for my girlfriend's birthday.  It makes use of the boost converter described in my Instuctable.  It was a bit of rushed build so I didn't have time to take pictures but here are the specs:

  • 5V input to boost converter from a USB connection, boosted to ~18V.
  • That 18V goes as input to a 10+W amplifier module.
  • The amp drives a 3" full-range driver for 100-20,000Hz output.
  • It's all housed in a purpleheart case that I turned on the lathe.
  • After drilling holes for the accessory ports, I filled around them with Sugru for a nice finish.  I also used Sugru to add some rubber feet.
I recently added a thick MDF base (not pictured) with an in-built battery compartment so that she can move it around with her laptop easily.

I'd planned to add a laser-cut grill to the front but, although I cut the grill, I didn't have time to make a lid to house it and then the wood shrank significantly after I turned it making it very difficult to add one at this stage.

Bluetooth is next on the list...