USB power analysis

Been doing some HVR-950q debugging for the last couple of weeks. Finally getting around to cleanup on some existing patches that haven’t gotten upstream, as well as investigating some new reliability problems.

Out of concern that one of my problems might be power related, I dug up some hardware I hacked together about four years ago.

[lightbox title=”USB power analysis” href=”../../blog/wp-content/uploads/2012/06/power1.jpg”][/lightbox]

[lightbox title=”USB power analysis” href=”../../blog/wp-content/uploads/2012/06/power2-168×300.jpg”][/lightbox]

Q: What does this rig do?
It lets you see how much power the device is consuming? In the second photo you can see the tuner is drawing 416 milliamps while tuning to an analog channel.

Q: Why should I care?
Power consumption is a good indicator that the device is working properly. It tells you if everything is powered up. It tells you if you’re over the 500ma power budget the USB port provides (which is theoretically possible if the registers are not programmed properly). It can tell you if you’ve got extra chips powered up which might cause a thermal problem or power instability. Once you understand how much current each component draws, you can even deduce things like how hard the tuner is working to lock onto a particular channel.

Since it’s purely a hardware solution, it lets you compare the behavior between Linux and Windows to make sure they are on-par.

Q: How do I build my own?
The picture is pretty self explanatory. I spliced open a 6″ USB cable that came with a tuner, cut the power line, and hooked it up to some banana clips from Radio Shack. A multimeter, a bit of heat shrink tubing, and voila! Don’t know which wire to cut? Since the cables are about a couple of bucks each, just buy four identical cables and take a guess (in my case, it was the red wire and I managed to get it on the first try).

Low tech, but quite effective…

Hoping to get this work wrapped up in the next few days. Then back to the saga of the HVR-1800 analog regressions….

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