This one kinda deserves a spot all to it's own, as things got a little hairy, and actually part of it still is.
Having a TV of some sort and a good sounding audio system to go with it was always part of the plan, and was right up there with how to power it and the like when it came to long term thinking. The output part of it came out very well, and feeding it (both power and media source) was quite a challenge.
First evaluations of what I was working with were a bit on the dismal side - just on and idle, everything was pulling just shy of 200W
This wasn't going to work, and actually, a test that failed miserably on more than one level showed just how bad it was - I managed to fall asleep, the TV didn't shut down like I was expecting it to, and I just happened to wake up just in time to not need to call the battery recycling place for a reservation... 11.0V, and the classic was reporting 20% SoC remaining. I couldn't find the switches for everything fast enough! :'(
The batteries recovered, it was their first (and hopefully last) trip below 50%, so not a super big deal, but clearly I had to trim the fat.
The TV is a 26" TV/DVD/Monitor combo that my parents donated to the project, and draws about 60W by itself. I haven't looked into converting this one to DC because I suspect the supply isn't as clear cut as a monitor or even typical TV, and the gains I'd get might only be in the 10 or 15% range overall. Not really worth digging into at this point, especially considering it's already mounted. That was enough fun in itself.
The audio setup I was using at the time of the test was also rather hungry, but it was known that neither of two components would be used in the final design - they were both AC powered as well. A Technics 50x50 receiver and a Radio Whack EQ. I kinda wish I could have readily thrown the EQ into the final design, as it doesn't use much if a DC supply were used, but that itself was the real issue... I know it needs a bipolar supply, and I just couldn't justify building one for it when I knew I could compensate elsewhere.
What replaced the Technics amp is a little 12V 30x30 Alpine unit a neighbor gave me. It sips power when idle, and is easily controlled externally.
The sub amp is a homebrew unit that puts out 60W as well, and although the supply is a little less than efficient (was one of my first attempts at a push-pull switching supply), it's stood the test of time and draws little enough when idle so as to be of little concern. It too has remotely controlled power.
At the heart of the system is my old cell phone, a Droid Razr, with a 32 gig SD card, making for a total of 40 gigs of onboard media storage. With the file sizes I'm using, that's quite a run for video, although I went and dug up the high res copies of my stash to get rid of pixelation.
The flow goes something like this:
4 bare 250 gig hard drives form the media bank. They are docked to my old TV box which now runs a very basic LAMP stack (web server), which the phone can then browse for files to be cached for later viewing/listening. The details on this section will come later, as there is a hiccup with the plan that still needs ironing out, but it does work approximately as envisioned.
Once in the phone, the files are played either by PowerAmp (for music) or the stock video player for TV/Movies. I need to seek out an offline FLV player as well, as a fair chunk of my collection is flash, and the stock player only seems to like MP4. Details, details.
The video takes one path out of the phone via HDMI into the TV, and the audio can go either via headphone jack or thru HDMI, as there's an A/B switch to select them. Also on the switch is independent left and right audio levels. These are there because I discovered that at low volume levels, the audio gets grainy due to limitations in the phone (presumably output stage). They allow me to drive the phone harder and keep a low volume higher quality output when desired. The independent volume controls were actually an "oh well" at first, but it turns out that the extra versatility they provide was a silver lining. I wasn't originally planning on balance control, but it worked out well.
After leaving the A/B, the signal gets split, goes directly into the Alpine, and out to the satellites. The sub signal goes thru a low pass and preamp before going into the sub's power amp. After that, magic happens
Both the TV and the phone (due to a path created by the HDMI cable) are on ground loop isolators, and once the system was running on a single point DC source (the same outlet), it went completely noise free with the exception of a small amount of hum when the grid charger is in high mode. Other than that, it's completely silent, crisp, clear, flat, and sounds AWESOME. I couldn't be happier.
The phone can of course be detached and used in any one of the original design methods, for low power days, out and about, whatever. Battery still hangs on for about 3 hours of playback, not bad considering I've beaten it senseless in its previous life as a phone supply.
The TV also accepts VGA, so I have the versatility that offers as well... the EeePC can do the FLV playback surrogately until I get the phone player sorted out completely.
All said and done, idle is around 85W now, the TV shuts down when the phone ceases to give it a video signal, and plans are in the works for an audio triggered master power control for the entire system so that the inverter will completely go to sleep after I do
The TV is mounted on a full axis swing arm, and is restrained by a simple but effective dual bungee cord system. Credit goes to the neighbor on that one, pretty clever.
Little tight, but it all fits!
Till next time...
Steve
