Logic Anaylzer for iPod accessories?

[harber]

I'm interested to learn how some of iPod accessories communicate.

I have one that plugs into the headphone jack - I was thinking of running it through a headphone extension cable, and exposing the wires inside the cable. I think I could attach something like the Salae Logic 8-channel logic analyzer available here and get a picture of what's going on. And then ... noodle on that for a while to figure out whatever I can.

Would that be a helpful tool for this purpose?
Would the DSO Nano oscilloscope be better? worse?

If anyone has any suggestions about how I could start to see (and interpret) what's happening on those lines, I'd love to hear.

I expect it to be a bit of work ... just looking for tools to help.

[BruceF]

I'd start by reading up a bit on Project Hijack. They've done a bunch of the work for you on this.

[harber]

Thanks for the pointer, Bruce! That Project Hijack looks pretty cool.

Too bad the hardware is not available, but I'll read their papers and see what I can learn.

It looks the "analog or digital" question depends on the device plugged in - it seems the phone could handle either one.

So, I'm still not sure if I want a logic analyzer or an oscilloscope.

Off to do some reading - thanks again!

[BruceF]

No problem... I saw that project a while back and it took a bit to dig it out of the corners of my Google-extended memory banks.

The hardware is available to purchase if you want, over at Seeed Studio. But yeah, if you're looking to answer the analyzer/scope question, the Hijack documentation looks like the place to start.

(and no, forumbot, this post is not spam.)

[harber]

To summarize the parts of the paper that bear on this question:

*Anything using the headphone jack is kind of a hack (which, of course, is awesome, but leaves all the details up in the air).
*It'll use the mic channel as signal from the device to the phone
*It'll use the two audio channels: one for power (by an app on the phone generating a tone, which is just a voltage, after all) and one for signal from the phone to the device.

So, scope or logic analyzer? Depends on the thing you're trying to get between.
*If you think that thing will send analog to the phone, you'll want an oscilloscope.
*If you think it sends digital, the logic analyzer's your thing.

So. I just need to decide which way I want to bet, and run with it.