IR remote volume control

[Andy Peters]

Our "home theatre" consists of a Mac mini, a TV, a DVD player and a game thing. For audio I have a pair of KRK Rokit 5 self-powered studio monitors. (These little things sound pretty great.) When watching streamed or download stuff from the Mac, it works great, with the Mac feeding the monitors. But the other devices can't feed the monitors, so their audio goes through the TV.

That's no fun.  I used the TV's digital audio output into a cheap DAC into the monitors, and that works, except: that output doesn't follow the TV volume control. I guess they assume that this digital audio output would go to a stereo receiver which has that control.

So I designed and built a little IR remote volume control that fits into a Hammond extrusion. Balanced in and out with THAT things, a TI PGA2320 which does the volume control, a two-line LCD for display, an SiLabs C8051F314 to read an IR receiver and a rotary encoder and run the whole show. Power is from a 16 VAC wall wart.

It's programmed to know the little Apple gumstick remotes, which speak the NEC code. It can also be switched to use the RC-5 IR code. I need to add a "pair" feature so it will respond to only one particular remote.

It's dead quiet, and does what it's supposed to with no fuss.

Here is what it looks like.

 

[Rochey]

excellent!

I'm envious that you got it all working together (and that you had the time and skillset!)

Cheers

/R

 

[Andy Peters]

excellent!

I'm envious that you got it all working together (and that you had the time and skillset!)

Daffyd, it could very well be TI's eval board for the PGA2320, except that I didn't use one of your microcontrollers or your differential inputs and outputs (I used THAT, although substitutions are easy).

One question that popped up, and maybe you can help, is this. I asked it on the TI E2E forum and another engineer had the same question: should an AC block be used between the driver/stage before the PGA2320 and the 2320's input?

Assuming that the gain-control stage is basically a potentiometer (albeit one implemented with trimmed resistors and a switch network), then a DC block might be recommended, even though I enabled the zero-crossing detection. I put a 47 uF cap between the THAT 1200 output and the PGA2320's input, and it has no measurable phase effect in the audio band. I suppose it's easy enough to test and compare the two channels, one with the block and one without. The data sheet makes no mention of such a cap.

-a

 

[Rochey]

Given that it's an attenuator, then bar so much DC that you get headroom issues, any DC should be attenuated, so you can DC block on the way out.

/Dafydd