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Hardware Hackers Reveal Apple's Charger Secrets
ptorrone writes "In this 7-minute video we explore the mysteries of Apple device charging. Usually, device makers need to sign a confidentially agreement with Apple if they want to say their charger 'works with iPhone / iPod,' and they're not allowed to talk about how the insides work. If you don't put these secret resistors on the data lines too, you get the dreaded Charging is not supported with this accessory. We demonstrate how anyone can make their own chargers that work with iPhone 4, 3Gs, etc."
Resistance is Futile
Is it wrong for me to get a bit hot under the collar, seeing a geek girl with such an impressive electronics workdesk?
Right to repair our own electronics though? (Or build interface devices)?
Lots of companies do this. APC puts a RS-232 serial port on a UPS but wait! They move the pins around so you need a special cable. Cisco used to have a product called the Gigastack that used a standard 6-pin Firewire cable, but no! Pins 1&2 were shorted in the "special" cables Cisco provided.
this is my sig
i hate when manufacturers do crap like this to keep peripherals locked into a more profitable licensing agreement. Apples tendency toward total control is one of the things i don't like about them.
tho other manufacturers are just as bad. i will never buy a Dell for my home for the same reasons. at work we had an Out of warranty gx 270 desktop. they were know for their bad capacitors in the power supply. so lo and behold the PS goes out. i have to spec a new one. at first i thought i would hop down to the local PC store and grabe a cheap PS for like $30 would work fine.
found out that the motherboards on those dells had different pin layouts from regular boards. the connector was the same as your usual PS but the lines were scrambled. if you plugged in a PS from the PC store you would fry the mobo. thus i would have to get a new PS from the dell store at a cost of $115 ..
we opted for a used PS from a 3rd party supplier for $30 instead.
wish companies would back off and be more open. the way things seem to go we're heaed back to the old at&t days when it took a court action just to add a funnel to your telephone handset http://en.wikipedia.org/wiki/Hush-A-Phone/
But the shown resistors don't look like the standard micro-USB connector. So is Apple breaking it's prommisses? Or am I missing something?
Doesn't it just use micro USB like all the other new phones?
I thought that the EU had forced all of the cell phone makers to adopt micro USB for charging and that they had complied by adopting the standard everywhere (not just in the EU).
I probably don't need to make this point here on /., but I think this is a great development. The convenience and cost saving to me as a consumer are substantial.
Has Apple managed to avoid this?
Most third party chargers I see for Apple hardware are Chinese knock-offs purchased for under 20$ from eBay. I somehow doubt these manufacturers signed anything.
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Reading the article, it appears that the purpose of the resistors is NOT to lock out manufacturers, but to inform the ipod of the amount of current to draw from the charger. They found different manufacturers using different values of resistors. From the looks of it, one resistor sets the amount, and the other resister serves as a "checksum of sorts, complementing the other resistor correctly to verify the value. Getting the value wrong could very easily cause a fire, so this is important to make sure you get it right.
This is not surprising, as USB does not allow variable voltage, and current is supplied completely on demand with no regard to the provider. So you either have your device set to draw a fixed amount of power (current) and limit your options to *1*, or you develop some simpler way to tell the device how much power (current) a device can demand from any given charger.
The only other option would be to use the data pins and actually communicate over the usb spec normally and outright tell the device how much power to draw. (which is actually already in the USB specs) Apple would have probably preferred to go this route, but that would significantly increase the complexity of the power adapters. All the people that are whining about Apple being nasty about this need to get some education. Apple's other two options were to make chargers cost more, or to not be able to offer both fast (wall power) and slow (AA batts) chargers.
The only group that's more thick-headed than the Apple zealots, are the anti-Apple zealots.
I work for the Department of Redundancy Department.
Is there a practical reason that the iPhone / iPod cannot be recharged and / or synced via a simple USB mico connector interface?
Yes... Profit!
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We all love to call out Apple when they design deliberate incompatibility into their devices, but there is a perfectly valid technical reason for what Apple is doing here, and, in fact, they are following a USB specification (which LadyAda unfortunaterly didn't even test).
Without data communications or when suspended, devices may legally draw no more than 2.5mA from a host, which is useless for charging. In fact, even if you're generous and pretend they're connected, devices are not allowed to draw more than 100mA without negotiating for a higher current, which requires actually talking to the host, and 100mA is still too little to charge properly. 500mA is the maximum allowed by the USB spec, but devices must negotiate it (there may be too many devices on the bus for negotiation to succeed).
Before there was a spec for "dumb" USB chargers, Apple used the resistors as a sentinel to avoid drawing too much current from undersized chargers in order to avoid damaging the host. This is a hack, but it works, and honestly, we're smart enough to figure out a couple resistors on the data lines. It's not like they're using crypto auth on the charger. They have a perfectly valid reason to do this. Devices which charge from "dumb" chargers aren't following the spec, though this is a common industry practice.
As it turns out, the USB-IF came up with a USB Battery Charging spec. The spec is long and boring, but it boils down to: short together the data lines (no resistors required) and you indicate that you're a dumb charger that can supply anywhere from 0.5A to 1.5A.
Guess what happens when you short the data lines of an iPhone 3G and supply 5V. Did Apple just follow a standard? Incredible!
(Yes, I'm not following the USB spec there by in turn using a USB cable to supply the 5V and not negotiating over its data lines. I didn't feel like grabbing a dedicated 5V PSU for the shot, so sue me.)
Funny, my Android phone does the same exact thing and it uses a standard USB micro interface. You need a special plug to get the full 1000ma charging, but it can use regular plugs too and charge at 500ma without frying anything.
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If that was the case and it wasn't for profit, why would they require a secret contract? I get why the resistors were initially added but I'm not understanding why it needs to be a trade secret.
WTF Slashdot, why do I have to login 50 times to post?
Is today bizzarro day?
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But there is nothing to stop them just drawing the 500mA if the right sort of charger is not detected. Refusing to charge at all unless the licensed parts are present is pure market control, nothing else.
You got modded insightful?
My N900 charges via a USB cable. It charges at 1200mA with the fast Nokia charger, at 500mA with the slow Nokia charger or PC USB port and at what appears around 300mA with a $2 Chinese car charger.
And they certainly don't charge third parties to provide them with secret recipes on how to make the chargers work.
Or naw... you are right, Apple never does anything wrong, just uncool people complaining about everything...
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it takes almost 8 hours [appadvice.com] to fully charge an iPad over a USB port. I'd rather plug it in for 5 hours to the Apple charger than wait so long
:)
Hmmmm...why would you be waiting? Why wouldn't you just go to sleep?
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There was a way to do this that didn't involve unsoldering and measuring the resistors.
Tests with an ohmmeter and visual inspection had already shown that the charger tied each D line to an independent voltage divider across the supplied voltage. This produces the (Thevenin) equivalent of:
- a voltage source at the same ratio to the supply voltage that the lower resistor's value has to the sum of the resistors' values,
- in series with a(n equivalent series) resistance equal to that of the two resistors in parallel.
Measuring the supply voltage and the unloaded voltage on a D line gives the resistor value ratio. You can measure the parallel equivalent resistance by either of two methods:
- Shut down the supply, short + and -, and measure the resistance from the D line to the shorted supply.
- Load the D line with a resistor to ground of known value that pulls the voltage down appreciably. (In the ballpark of cutting it in half is ideal.) Measure the amount it droops (and recheck the power supply voltage in case you pulled that down a bit, too.) This presumes the pullup resistor can handle 2x the normal current and 4x the normal power dissipation, for the duration of the test.
With those two measurements you can calculate the resistor values. If they fall near standard values it provides a sanity check on your calculations and measurements. You only have to pull 'em off if there's an additional "black box" component hooked to the D lines that might foul up your measurements.
(Of course if you already have the tools handy, pulling off and measuring the resistors may be easier. It also lets you check that there wasn't something else hidden in the circuit that you missed.)
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This cannot be! Apple is about supplying the best customer experience, about rolling out magical devices to the masses to free them from the bondage and slavery of technology as imposed by those proprietary, secretive for-profit companies!
Browsing at +1 - no ACs, I ignore their posts. So refreshing!
Same with Nokia...
or any other phone that uses the standard USB Spec for charging.
Calling someone a "hater" only means you can not rationally rebut their argument.
Apple doesn't follow standards, they set them. Following standards is for open, cooperative people, like Microsoft.
refusing to charge or just SAYING it's not charging?
i have a USB hub (unpowered) that works fine for syncing. last night I got the "I'm not charging message", but the next AM, it was charged (up from about 75% or so)..
people who get "official" apple chargers are the same crowd who buys Monster cables. fuck'em