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Hijack - iPhone Sensors Thru Audio Jack

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Re: Hijack - iPhone Sensors Thru Audio Jack

#31

Post by mkopinsky »

tekromancr wrote: post #19
acgourley wrote: post #17

Earlier quoted context omitted.

It's probably no coincidence it's right out of human hearing range. Most headphone drivers response curve are likely designed to be less efficient at that freq, and thus need more power to create the same loudness. the iPhone's audio driver probably takes this into consideration and drives those frequencies with more power to compensate. Just a guess, I'm sure they arrived at it purely through trial and error, and we…

Minimally annoying my ass. If you are still young enough to hear it it's downright painful!

How young is young enough to hear 22 kHz? I am 25 and can barely hear 14kHz. http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearin... In the comments section there people claim to be able to hear 20 and 21, but it seems like not many can hear 22.

Re: Hijack - iPhone Sensors Thru Audio Jack

#32

Post by sopooneo »

feralchimp wrote: post #13

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…

Wouldn't it be a simple relationship: higher frequency -> higher energy?

Re: Hijack - iPhone Sensors Thru Audio Jack

#33

Post by tomn »

feralchimp wrote: post #13

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…

I don't know the theory behind this stuff, but here it goes:

Headphone jacks tend to have a capacitor in-line with the output terminals to get rid of any DC bias -- this can cause problems like battery drain, lots of noise when you plug headphones in, and damage to the driver coil of headphones -- not good!

I like to think of a capacitor like a shock absorber, with the length of the shock absorber being like the voltage it's currently storing. If you push on one end of a shock absorber, the larger the force (current), the larger the rate of change of voltage (length), so this analogy might be useful.

Imagine holding on to one end of the shock absorber while someone else tries to move it back an forth at a given frequency. If they try to move it back and forth slowly, the maximum force (current) is going to be low, and so the total energy will be low and you won't get shaken much -- the shock absorber will just change length (voltage).

If they try to move it back and forth quickly, the force (current) will be much higher, and so you can extract a lot more energy from it.

I believe it's the same reason portable devices have poor bass response.

Re: Hijack - iPhone Sensors Thru Audio Jack

#34

Post by lbotos »

mkopinsky wrote: post #31
tekromancr wrote: post #19

Earlier quoted context omitted.

Minimally annoying my ass. If you are still young enough to hear it it's downright painful!

How young is young enough to hear 22 kHz? I am 25 and can barely hear 14kHz. http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearin... In the comments section there people claim to be able to hear 20 and 21, but it seems like not many can hear 22.

Don't forget with tests like the one that you've linked it depends on your speaker's response to get an accurate reading.

Re: Hijack - iPhone Sensors Thru Audio Jack

#35

Post by marvin »

mkopinsky wrote: post #31
tekromancr wrote: post #19

Earlier quoted context omitted.

Minimally annoying my ass. If you are still young enough to hear it it's downright painful!

How young is young enough to hear 22 kHz? I am 25 and can barely hear 14kHz. http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearin... In the comments section there people claim to be able to hear 20 and 21, but it seems like not many can hear 22.

In practice I'm pretty sure it's more about exposure to loud noises than actual age, and these increase as you age. I know I was able to hear 20kHz at 16, but probably down to 17kHz or so now at 25.

In other words, if you've been to a couple of rock concerts with no earplugs then all bets are off.

Also worth noting that most speakers play 0.5dB below the actual signal at 20000Hz, where anything above that usually isn't specified. So you need specialist audio gear or some measuring equipment to actually try to listen to really high frequencies.

Re: Hijack - iPhone Sensors Thru Audio Jack

#36

Post by codehero »

joezydeco wrote: post #8
automach wrote: post #4

Earlier quoted context omitted.

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

" 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?

I wrote an app that uses this cable. You CAN distribute an app using serial communications, but ONLY with a custom cable variant created by Redpark. This custom cable will ONLY work with your app, and your app will only work with this custom cable. Apple will approve this app because Redpark has done the legwork of MFI compatibility. What the web page points to is only a "evaluation" system, not production ready.

Re: Hijack - iPhone Sensors Thru Audio Jack

#37

Post by joezydeco »

codehero wrote: post #36
joezydeco wrote: post #8

Earlier quoted context omitted.

" 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?

I wrote an app that uses this cable. You CAN distribute an app using serial communications, but ONLY with a custom cable variant created by Redpark. This custom cable will ONLY work with your app, and your app will only work with this custom cable. Apple will approve this app because Redpark has done the legwork of MFI compatibility. What the web page points to is only a "evaluation" system, not production ready.

Thanks for that information. It's hard to get any understanding of what the whole Apple developer program is regarding the dock connector. Obviously the keynote dream of "look at all the things we'll be hooking up to iPhone/iPad!" is never gonna happen.
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