I'm finally finished with my On Air lamp prototype. The goal of this project was to build something that would indicate when I have the camera and mic rolling in my office without any intervention on my part (basically, all I need to do is start a meeting and it goes on, or end it and it goes off). I've managed that.
It took me quite some time to figure out how to get Windows 10 to tell me when the microphone is in use. The key is in the registry keys located in the registry hive for the current used found in SOFTWARE\Microsoft\Windows\CurrentVersion\CapabilityAccessManager\ConsentStore\microphone.
In this hive there is at the top level, a hive of keys for each Microsoft Store app, and beneath it, another hive of keys found in the NonPackaged hive.
If you inspect the registry with RegEdit, you will see that each hive under that key looks something like this:
The key (pun intended) key is LatUsedTimeStop. When this value is 0 for any application, that application is presently using the microphone. When it's done, that value will be a Windows timestamp (the number of 100 nanosecond intervals since 1/1/1601 UTC).
I wrote a little Java program called OnAir that scans the registry, checks for the Microphone being in use, and sends the appropriate messages to the wireless controller to adjust the state of the lamp.
I tested it with almost all of my headsets (I have four in my office of various types), and it works with any of them, and with any application that uses a microphone.
To make this code work I needed to be able to access the registry from Java. There's a lovely little Java package that does this called JNA. The dependencies to include it are below.
<dependency>
<groupId>net.java.dev.jna</groupId>
<artifactId>jna</artifactId>
<version>5.10.0</version>
</dependency>
<dependency>
<groupId>net.java.dev.jna</groupId>
<artifactId>jna-platform</artifactId> <version>5.10.0</version>
</dependency>
I suppose I could have used this as an opportunity to write in .Net, but realistically, I was just looking to get the lamp off my desk, and to do that, I needed to finish the prototype.
There's so much more I could do to finish this. The application could use a UI to indicate the state of the lamp, and to activate/deactivate it for certain applications, and indicate which application is using the microphone. The app itself should run as a service. The electronics could be cleaned up so that I don't need two USB cables, and the wireless component could be mounted inside the lamp. For now, it's good enough for what I wanted, so I'm calling it done, and declaring "Ship it!".
