
Hijack - iPhone Sensors Thru Audio Jack - J3L2404
http://www.seeedstudio.com/wiki/index.php?title=Hijack
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feralchimp
_The HiJack energy harvester can supply 7.4 mW to a load with 47% power
conversion efficiency when driven by a 22 kHz tone from the output of a single
audio channel through the iPhone/ipad/itouch headset port, no extra energy
source is needed. The name "Hijack" refers to this energy harvestign method._

Can someone here explain the functional significance of the 22kHz tone? It
would be more intuitive if they'd said "an audio signal driven at the
headphone port's maximum volume." Why would there be more harvestable energy
in a max-volume 22kHz tone than a max-volume 11kHz tone? Or might this be to
avoid accidentally blasting the user with a super loud output tone (i.e. in a
more audible range) from the device speaker?

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jonsen
The tone AC signal has to be converted to DC power supply. A higher frequency
means smaller components needed to do the conversion. Size roughly inverse
proportional to frequency. So they probably chose close to the highest
frequency possible on the audio output.

~~~
mdda
If the samples are put out at CD rates (44.1KHz) then 22.05KHz is the highest
AC frequency available.

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bwarp
I think this is a novelty at best.

The electrical interface standards may change between devices (voltage/current
sink ability) and even between software releases (power saving etc) resulting
in a sudden "it stops working" moment.

The basis of it is also flawed on the fact that it's a workaround for a closed
platform at which point it's probably better to just use an open one.

Hack yes. Novelty yes. Don't build anything important with it.

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yabai
Looks interesting...but what is the real application?

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msutherl
Prototyping mobile accessories! When you're working with hardware, building
things to make things talk takes _a lot_ of time. This makes it easier.

It's also useful for student projects. I got one of the original wiretaps when
they were giving away their first batch for a prototype medical device (we
didn't end up using it in the end because it was still too much work).

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antirez
great idea / technology, lame page. Would love to see a decent article on the
topic, with specifications about the minimal number of components to do
something useful (enough to use the input jeck ADC in a decent way), and some
example application that you can actual build easily with schematics. IMHO a
good show case could be a termometer that you can plug to your iphone with
minimal components, using a classic temperature sensor that changes the
resistance with difference of temperature.

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tekromancr
I suppose you could use this to make a generic ir remote. That was one of the
coolest things that all my old palm PDAs could do, and has always been a big
dream feature on the iPhone.

~~~
mirkules
That has already been done: [http://rtfms.com/episode-4-turn-your-
iphoneandroid-mac-pc-pl...](http://rtfms.com/episode-4-turn-your-
iphoneandroid-mac-pc-player-etc-into-a-universal-remote.htm) albeit without
HiJack

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joshma
This is really cool! I've been thinking about fiddling with Square readers to
read card data, but something like Hijack makes this so much easier.

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joezydeco
The O'Reilly book "iPhone Hacks" also has schematics and details on how to
create a headphone jack interface.

~~~
msutherl
...which requires a Cypress PSoC chip for which you need to buy a $100+
programmer and use their Windows-only IDE.

~~~
joezydeco
The concept is pretty well explained (FSK mod/demod). Someone enterprising
enough can implement it in ways that don't require the Cypress equipment.

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Anechoic
What's the advantage of using the headphone connector rather than the dock
connector?

edit: thanks all, I forgot about the licensing requirement for the dock
connector

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automach
Using the Dock connector involved paying Apple a licensing fee. This
circumvents that, and it's similar (although more involved) to how Square's
card readers work.

There is already an iOS serial cable though, which I would think would be a
better option for many projects:

<http://redpark.com/c2db9.html>

~~~
joezydeco
_" Under current Apple policy this cable may not be used with apps sold on the
App Store."_

That's an odd condition of Apple's terms. Why is this so? If I go through the
process of designing and approving a hardware device, I can't sell an app to
go with it? Or do I have to provide the app in tandem with the device?

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duskwuff
"may not be used with apps sold on the App Store" probably just means "Apple
will not approve an application which uses this cable for sale on the App
Store".

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joezydeco
But _Apple approved the cable_. Get the paradox?

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angusgr
Where does it say that Apple approved the cable? It seems to me like they're
deliberately avoiding any step that requires Apple approval.

~~~
joezydeco
It's right on the front page.

You can't use the "Made for iPod" label on your product unless it's Apple
approved and has an Apple-supplied chip in the dock connector.

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spiritplumber
Neat, we've been doing that for a while for Android.

<http://phinominal.com/sited/>

