Coupling a home made microphone to Bluetooth

I stumbled across a tweet a few months ago from @helenleigh who was doing/had done a presentation at Hackaday's Remoticon, showing the world how to make your own microphone using mostly materials found around the home. This got me really intrigued, since I have an affinity for using articles out of the realm of their original intent.

So I watched the video on YouTube Remoticon 2020 // Finding Sound and Making Microphones Workshop and then went to work acquiring the supplies. Our local dollar store proved instrumental in supplying the quilting hoop and hair bands. I could have used ones we already had at home, but I do want to get along with the rest of the family. We did have enough binder clips, I also had a spare USB cable, as a matter of fact, I probably have a box full of them, but then again, who doesn't?

So I got to work and built the mic, using a slightly different method than Helen. Instead of rubber bands, I used hair bands, no need to tie knots. Also, rather than plastic, I used the inner circle cut out of an aluminum pie plate. Plus the aforementioned USB cable (which is shielded to prevent the leads from picking up hum.)

The only real electronic components are 2 piezo pickups, which I got from Amazon (in a pack of multiples).

I didn't have an amp of any sort to plug it into, and connecting the output from the mic straight to a set of headphones barely produced any output, so I hunted around for a preamp circuit. I found this:https://samtechpro.blogspot.com/2013/12/dynamic-mic-pre-amplifier.html

I simply doubled up on the circuit to make it stereo (ya gotta be professional about these things), prototyped it on a breadboard, it worked, so I got to transferring it to KiCad (version 5.1.8) 

Not being too familar with KiCad, it took me a lot longer than I anticipated, but here is the design seen from the bottom and then from the top: 

 

 

Next, I undertook the usual routine of creating my own PCB, always fraught we difficulties aplenty. In the end though, I ended up with a nice looking print and PCB.

I mounted the components and decided that the output would go to a 3.5mm jack. The 5V power would come to the board via a micro USB jack. Next, I installed all this in a small box. Finally, I hooked it up to a very small set of speakers and it worked.

Not being satisfied with that, I decided to try and employ a set of Bluetooth transmitters and receivers. Not having any idea if it would work, I tried to get the two to pair, and surprise, surprise, they did. The transmitter is an Aigital Bluetooth transmitter, the receiver is SZMDLX transmitter/receiver combo, the latter being used by me obviously only in receive mode.

I hooked up the mic to the input of my preamp, the output to the Bluetooth transmitter. Then the Bluetooth receiver was plugged into the 3.5mm AUX jack on my computer. Upon insertion, a MaxxAudioPro screen popped up, asking me what sort of device I was plugging in. I chose Microphone in. Then over to Control Panel, Hardware and Sound, Manage Audio Devices, Recording, Jack Mic, then choose Properties and place a tick mark in the Listen checkbox. And voila, I heard my own voice!

This way I can record as well. I must say, the sound quality is pretty decent. Here is a sample:

Additionally, some photographs of how it all looks:

Microphone front above, microphone back below.

The complete setup. For microphone stand, I used a slightly modified cell phone holder, bought at the dollar store for a couple of bucks. Plus, of course, a binder clip.

From left to right, battery pack, preamp in a case, Bluetooth transmitter, Bluetooth receiver, laptop. The circuit board on the top is a prototype of the final result.