Nui – IR Volume Controller
Nui is an IR controlled volume controller for analog audio. It sits between your audio source and speakers and can amplify or reduce the volume using IR commands (and eventually BLE).
Why do I need this?
It all started because I have my trusty Logitech Z-2300 speakers and subwoofer I purchased back around 2004/5. They still work great, but instead of being on my computer, they are used for my TV. Unfortunately, the TV’s line out doesn’t honor the TV’s volume and is always outputting at max volume. Sure, I can get up and change the volume on the speakers themselves, but wouldn’t it be more convenient to do it with the TV remote?!
That’s how the Nui project started. It sits between my TV and my speakers and now I don’t have to get up to change the volume 😀
Initially, I decided to use a [Teensy][https://www.pjrc.com/teensy/] microcontroller so I could take advantage of the Arduino-IRremote library (Started by none other than Ken Shirriff!). Not having to write my own IR decoder made getting started super easy
I wanted to use the project not only to solve my volume control problems, but to learn some new things. I hadn’t dealt with analog audio before or negative voltage rails on my projects, so it was a fun way to try them out.
After lots of searching and reading about audio amplifiers, digital potentiometers, and many other things, I decide to go with TI’s PGA2311. They call it a “Stereo Audio Volume Control”, which is just what I needed. It takes a stereo audio input and can both amplify and attenuate the volume. It is controlled over the SPI bus, which makes it easy to work with.
One of the cool features is the zero-cross detection, which makes sure it only changes the volume when the signal is crossing 0V, which gets rid of any popping noise due to the sudden gain change. The device also has a hardware mute, which is nice.
[Un?]fortunately, the PGA2311 needs both a +5 and a -5V rail. As I mentioned before, this is all about learning, so bring it on! I searched around and found the Microchip TC7660S, which is a “Super Charge Pump, DC-to-DC Voltage Converter” that will take my 5V input and convert it to a -5V output. It also has the option to run at 45khz, which should minimize any audible noise generated by it.
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