A bare bone Push To Talk USB-microphone.
More or less just the LUFA USB audio device sample enhanced by analog sampling and an enhanced microphone "shield". No driver installation is needed.
Beside the schematic being so simple this USB-microphone is immediately recognized by Win10 and cooperates with all major brand audio/video sharing platforms. What shall they do else with a regular USB-microphone? The audio quality is surprisingly good and several feedbacks confirm it is comparable with way higher priced industry products. Maybe some initial mismatch until the audio chat app has adjusted to the mic takes a fraction of a second and could get some more attention.
Microphones build into the computer are fine but there is no control who listens to you when you do not excpect it. To get back privacy the internal mics are reliably disabled.
With the Coronafon a pushbutton gives ultimate control if the computer is allowed to listen - until you simply unplug it.
Check the LUFA sample for details on USB. The audio control is quite simple. Let the ADC of the AVR sample the audio. If the pushbutton is enganged feed those samples to the USB. If not, just feed a zero to the USB; and get your audio chat app claiming about this extreme silence :badgrin:.
Since there is no way to enter into the booloader from the microphone code, there is also no way for hackers to get the ProMicro reflashed without your awareness. A physical hardware reset of the board is necessary to get into the bootloader, if the ProMicro should get reused by another project.
Use the plain old WinAVR toolchain and the makefile provided. Alternatively you might want to use the plain hex file straight out of the repo folder.
Adjust the COM-port settings inside flash_it.bat to match your setup, then run this batchfile from the console. The hardest part is figuring out which COM port it got assigned to when in bootloading mode. Maybe a hardware reset needs to be given before reflashing is started. Of course, Caterina (Arduino bootloader) needs to reside there.
1 x Sparkfun ProMicro, Arduino Leonardo, PRJC Teeny 2.0, ... 16 MHz variant
1 x MAX9814 microphone breakout board
1 x pushbutton
2 x 10kOhms, 5% but tolerance does not matter
2 x 1nF, >10V (just to be sure), 10% but tolerance does not matter
"On Air" LED and its resistor are optional
The MAX9814 is adjusted to mid range gain. The RC low pass filter cares for anti aliasing. Without this simple filter the noise floor of the digitized sound will rise dramatically. A setup on a solderless breadboard just will do.
Well, this makeshift thing got very handy during some pandemic lockdowns and remote work sessions.
Dean Camera, LUFA project https://www.fourwalledcubicle.com/LUFA.php