6 ms·

Hijack - iPhone Sensors Thru Audio Jack

160 points by J3L2404 15y ago

Anechoic 15y ago
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
- riobard 15y ago
  License fee and dependence on Apple? See this http://www.quora.com/Apple-Inc-2/What-is-the-royalty-Apple-charges-for-devices-which-use-its-30-pin-connector-for-iPhone-iPod-or-iPad http://www.quora.com/Apple-Inc-2/What-is-the-royalty-Apple-c...
- automach 15y ago
  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 http://redpark.com/c2db9.html
  - joezydeco 15y ago
    " 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?
    - duskwuff 15y ago
      "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".
      - joezydeco 15y ago
        But Apple approved the cable. Get the paradox?
        angusgr 15y ago
        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 15y ago
        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.
    - codehero 15y ago
      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.
      - joezydeco 15y ago
        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.
- durkie 15y ago
  i'd think potentially being android/whatever compatible as well.
- MaxGabriel 15y ago
  While I think the other commentators have the main reasons, I'll add that this solution also let's you charge the iPad at the same time.
joezydeco 15y ago
The O'Reilly book "iPhone Hacks" also has schematics and details on how to create a headphone jack interface.
- msutherl 15y ago
  ...which requires a Cypress PSoC chip for which you need to buy a $100+ programmer and use their Windows-only IDE.
  - joezydeco 15y ago
    The concept is pretty well explained (FSK mod/demod). Someone enterprising enough can implement it in ways that don't require the Cypress equipment.
joshma 15y ago
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.
bwarp 15y ago
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.
- nupark2 15y ago
  Harvesting power is a bit questionable, but in terms of an input mechanism, Square built their reader on the idea. As far as it being a hack for a closed platform, I'm not sure why that matters if your goal is to interface with the primary mobile phone platforms. This solution works, and if you need something more professional, working with the dock connector itself isn't an burden any more insurmountable than dealing with injection molding or other product design and manufacturing concerns.
  - colinloretz 15y ago
    Agreed. Using the dock connector with a legitimate product requires you to join Apple's "Made for iPhone" program. For a device like Square that works on multiple platforms, the audio jack is a common interface and the Square reader has the benefit of requiring little (to zero) power to function as it consists of a magnetic head that works when a card slides across it.
- yabai 15y ago
  Looks interesting...but what is the real application?
  - nemik 15y ago
    Well there is a small company that created a credit card reader using it to enable smartphones to act as Point of Sale machines. They call it "Square".
  - msutherl 15y ago
feralchimp 15y ago
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?
- acgourley 15y ago
  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 were happy to find that it's also a frequency that will be minimally annoying if a headphone happens to be plugged in when the tone is played.
  - tekromancr 15y ago
    Minimally annoying my ass. If you are still young enough to hear it it's downright painful!
    - mkopinsky 15y ago
      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-hearing-test/ 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.
      - 15y ago
antirez 15y ago
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.
tekromancr 15y ago
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 15y ago
  That has already been done: http://rtfms.com/episode-4-turn-your-iphoneandroid-mac-pc-player-etc-into-a-universal-remote.htm http://rtfms.com/episode-4-turn-your-iphoneandroid-mac-pc-pl... albeit without HiJack
spiritplumber 15y ago
Neat, we've been doing that for a while for Android. http://phinominal.com/sited/ http://phinominal.com/sited/

160 points by J3L2404 15y ago

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

riobard 15y ago
License fee and dependence on Apple? See this http://www.quora.com/Apple-Inc-2/What-is-the-royalty-Apple-charges-for-devices-which-use-its-30-pin-connector-for-iPhone-iPod-or-iPad http://www.quora.com/Apple-Inc-2/What-is-the-royalty-Apple-c...
automach 15y ago
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 http://redpark.com/c2db9.html
- joezydeco 15y ago
  " 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?
  - duskwuff 15y ago
    "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".
    - joezydeco 15y ago
      But Apple approved the cable. Get the paradox?
      - angusgr 15y ago
        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 15y ago
        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.
  - codehero 15y ago
    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.
    - joezydeco 15y ago
      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.
durkie 15y ago
i'd think potentially being android/whatever compatible as well.
MaxGabriel 15y ago
While I think the other commentators have the main reasons, I'll add that this solution also let's you charge the iPad at the same time.

joezydeco 15y ago

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

msutherl 15y ago
...which requires a Cypress PSoC chip for which you need to buy a $100+ programmer and use their Windows-only IDE.
- joezydeco 15y ago
  The concept is pretty well explained (FSK mod/demod). Someone enterprising enough can implement it in ways that don't require the Cypress equipment.

joshma 15y ago

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.

bwarp 15y ago

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.

nupark2 15y ago
Harvesting power is a bit questionable, but in terms of an input mechanism, Square built their reader on the idea. As far as it being a hack for a closed platform, I'm not sure why that matters if your goal is to interface with the primary mobile phone platforms. This solution works, and if you need something more professional, working with the dock connector itself isn't an burden any more insurmountable than dealing with injection molding or other product design and manufacturing concerns.
- colinloretz 15y ago
  Agreed. Using the dock connector with a legitimate product requires you to join Apple's "Made for iPhone" program. For a device like Square that works on multiple platforms, the audio jack is a common interface and the Square reader has the benefit of requiring little (to zero) power to function as it consists of a magnetic head that works when a card slides across it.
yabai 15y ago
Looks interesting...but what is the real application?
- nemik 15y ago
  Well there is a small company that created a credit card reader using it to enable smartphones to act as Point of Sale machines. They call it "Square".
- msutherl 15y ago

feralchimp 15y ago

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?

acgourley 15y ago
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 were happy to find that it's also a frequency that will be minimally annoying if a headphone happens to be plugged in when the tone is played.
- tekromancr 15y ago
  Minimally annoying my ass. If you are still young enough to hear it it's downright painful!
  - mkopinsky 15y ago
    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-hearing-test/ 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.
    - 15y ago

antirez 15y ago

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.

tekromancr 15y ago

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 15y ago
That has already been done: http://rtfms.com/episode-4-turn-your-iphoneandroid-mac-pc-player-etc-into-a-universal-remote.htm http://rtfms.com/episode-4-turn-your-iphoneandroid-mac-pc-pl... albeit without HiJack

spiritplumber 15y ago

Neat, we've been doing that for a while for Android. http://phinominal.com/sited/ http://phinominal.com/sited/