I have a fairly old-school stereo system. It's based on an old NAD Model 1000 preamp which is basically a fancy switch with volume and tone controls. Inputs from the AM/FM tuner, CD player, Mac mini (which is our DVR and DVD player!), cassette deck and cable box are on the back. It's got two parallel output pairs (L and R) that follow the volume control. One set of outputs feeds my Genelec 1031A self-powered studio monitors.

It all works well, except that it doesn't have remote control for the volume or a mute function. But I'm an engineer. I can fix this.

So Radio Shack has these IR receiver modules and I have a handful of SiLabs 8051 boards and TI has SPI-controlled stereo volume control chips. The Genelecs have balanced inputs on XLR connectors, so I'm using a couple of TI DRV134 drivers for the outputs.

I'll take one of the tape-monitor outputs (which don't follow the volume control), plug 'em into my gizmo, and feed the speakers from the balanced output.

I've got some code that handles the simple Philips-style RC5 code (no weird preambles or anything) which I've programmed the Aux part of my cable-box remote to generate. I dug out my SiLabs '226 devel board, which already had my LCD interface happening, and soldered on the IR receiver module. Pressing Vol Up and Vol Down updates the gain variable and sends it over SPI to the volume control chip. Pressing Mute toggles the volume control chip's mute input. The display is updated with the status.

Time to build the analog board. I'll post the code and schematics when it's all working.

-a