Bluetooth connected communicator for your chest.
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This project won't have too many moving parts. Although our first intent was to get a BLE chipset and integrate it with some basic hardware to make the badge live, it turns out the chips we were looking at supported data only and weren't going to work for audio communications.
So we punted and picked up a Jabra earplug to hack and add to the badge. To get it done, we need to extract the electronics, build a small amplifier for the speaker and design the badge to be 3D printed.
Soldering the amplifier circuit, dead bug style.
Knowing we need to amplify the signals for the speaker, we built a small Darlington amp using transistors. It wasn't terribly great. The voltage loss was high and we didn't get a usable amount of audio. We are not yet happy with the final results of the speaker volume so are now researching a flat piezo speaker to see if that will produce better results. From there, we plan to then miniaturize the speaker, which will require a change in the driver circuit.
I can't say I'm thrilled with how Slic3r built the support under the badge. I snapped a razor trying to get it out. I decided to reprint and deepen the design to make it taller so the badge won't stick out so far from your chest. Once it was done, I took a dremel to the back to remove the extra ABS and then used a 3/16" bit in the drill press to drill an access hole for the single button on the BT device.
Working on the badge dimensions, I took a digital caliper and measured a few bits on the earpiece. It's roughly 46.51 x 16.09 mm and shaped like a surfboard. The narrow end is about 5.14mm tall while the other is about 12.38mm. The microphone is encased in rubber. It's about 12.90 x 16.26mm and 7.30mm deep. I decided to mount it at the top of badge where it's behind the face and not visible. Depth will be fine because the battery is deeper.
I'm not much of a CAD kind of guy so I fired up Tinkercad and imported the STL I found. I carved out a few boxes and then rounded the corners with four ovals of the proper dimension. I then subtracted this from the back of the badge making sure none of the negative space popped out to the front. I then carved out the space for the microphone and a 1.2 mm groove for wires between the main circuit board and the mike. Not sure yet about speaker placement.
I'm now printing the updated badge to test fit the components.
Getting a seriously late start because we didn't get the bluetooth hardware until Friday, 4/25. I sat down on Sunday and pried apart the case. I then printed the badge I located at 
Print the shell. We obtained the original design from Thingiverse and then removed material from the back to mount the Bluetooth device and microphone. The current version can be found on github at https://github.com/TampaHackerspace/3D-Print-and-Model/tree/master/STNG%20Communicator
We printed the shell using ABS. To obtain a more finished look, try an acetone bath to smooth the surface. Once the acetone has completely evaporated and the badge is completely dry, apply metallic paint to the visible surface.
Solder the amplifier circuit, dead bug style.
Assemble the badge
Tampa Hackerspace
That amplifier circuit is not how it's done, no good for audio. Best bet is copy a design from somewhere else, or else just buy a premade amp. The LM386 is an 8-pin chip that provides nearly everything you need to produce around a watt from 6V, or less from a lower voltage. It's quite old, and there's newer amp chips available, perhaps one of those would be good.