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Need help reverse engineering a PCB

Daniel Kuntz

Jul 1, 2015
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Hello, I'm new to the forums. This is my first post.

I'm designing a cable that will allow the user to be able to transfer power between two mobile devices, regardless of whether they are an iPhone or an Android device. I have already figured out how to transfer power one way through a cable from Android to Android and Android to iPhone. It's quite simple; one end of the cable just has to have pins 4 and 5 on the micro USB plug shorted, creating an OTG cable on that side. This triggers the device attached to the OTG end to send power out of the cable, thus allowing power to be transferred from an Android device to an iPhone or an Android device to an Android device.

The problem I'm having is figuring out how to take power from an iPhone. I am 100% certain that this is possible. I know this because you can take the Apple Lightning to USB camera adapter and plug it into an iPhone or iPad, and then plug a standard Lightning or Micro-USB cable into it and be able to take power from an iPhone or iPad. I can take a video demonstrating this if necessary.

When I simply solder two lightning cables together so that there's male Lightnings on both ends, this is not the case. Nothing happens. No power is transferred anywhere. The Apple Lightning to USB camera adapter contains a PCB that somehow instructs the iPhone to transfer power OUT of its Lightning port. I essentially need to reverse engineer this PCB.

I also an 100% certain that it is possible to reverse engineer the PCB, because it looks like someone has already done it. I found online a Lightning to Lightning cable that claims to be able to transfer power from one Lightning device to another. I ordered one, and I tested it and it does what it's advertised to do. I took it apart and found a PCB inside, which presumably does something similar to the one found in the Apple Lightning to USB camera adapter. I took some detailed pictures of this PCB so anyone who's willing to help me could take a look.

I've been sorting out technical issues with my Chinese supplier for about two months now, and the only issue I have left is figuring out how this PCB is constructed, and constructing a diagram for my supplier so it can be mass produced.

Your help is greatly appreciated.
 

Arouse1973

Adam
Dec 18, 2013
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Hello
Can you take a nice picture of the PCB on both side, we might be able to work something out.
Adam
 

Daniel Kuntz

Jul 1, 2015
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It doesn't look like there's anything too complex on it. Looks like there's a 555 timer, a capacitor, a diode(presumably to keep current flowing in one direction) on one side. The other side looks like it has a few capacitors and some other components I don't recognize. Please excuse me if I'm wrong, I'm not extremely well versed with this kindDSC08158.JPG of stuff.


DSC08159.JPG
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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can you read the markings on the chips? I'd be very surprised if the 8 pin one is a 555.
 

Daniel Kuntz

Jul 1, 2015
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The 8 pin doesn't have any markings. The markings on all of the other chips look like they're pretty visible in the pictures.
 

Arouse1973

Adam
Dec 18, 2013
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LOL 555 Timer. Yeah I doubt that also. This is going to be a dedicated IC, could even be a special made for them. I am guessing the 6 pin device is some kind of switcher? I think the only way your going to be able to work this out is to get a data analyser and see what data is sent when power is requested. I have used USB sniffing software before, this can be quite handy.
Adam
 

Daniel Kuntz

Jul 1, 2015
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I bought this cable for $3.50. Don't you think something like this would cost more if there's dedicated IC's?
 

davenn

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Sep 5, 2009
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Don't you think something like this would cost more if there's dedicated IC's?

no, not when they are made by the zillions in some chinese factory

without info on those 2 IC's there no way to reverse engineer it
 

KMoffett

Jan 21, 2009
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Because of the coil, below the 6-pin IC in the first photo, I think it's some sort of switch mode? buck? boost? converter? power supply.
I hope the cable wire...and what's on the other end...is worth the $3.50 to you Daniel. ;)

Ken
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Gee, the soldering on that thing is awful.

And it's probably worth noting that only 4 pins are soldered on the SO-8 package. That makes me suspect that the SO-8 package is just a mosfet.

The inductor (which is damaged) is most likely 4.7uH
The devices marked S1 and S4 could be all sorts of diodes, but are most likely Schottky diodes.
The various capacitors could be removed and have their values directly measured.
I have no listing for the 6 pin device, but if the SO-8 device is just a mosfet then this will be a switchmode controller.

It seems unusual that the device would have an external mosfet, so I'm sure there's more mystery there.

After you've removed and measured all the components (check the forward voltage on the diodes) then you'll be able to make out the wiring pattern which is heavily obscured by the solder mask but also by the components. I would rub the board against some fine emery board until all the tracks are clearly visible (unless you can make them out better than I can).

After this, you can start to draw a circuit diagram. This may reveal more about what the components are.
 

Martaine2005

May 12, 2015
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I've been sorting out technical issues with my Chinese supplier for about two months now, and the only issue I have left is figuring out how this PCB is constructed
I can certainly see why you are having technical issues. You are probably communicating with a 5 year old who has a pocket flamethrower.

Martin
 

Martaine2005

May 12, 2015
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  • All 8 pins are used for signals, and all or most can be switched to be used for power.
  • The outer plug shell is used as ground reference and connected to the device shell.
  • At least one (probably at most two) of the pins is used for detecting what sort of plug is plugged in.
  • All plugs have to contain a controller/driver chip to implement the “adaptive” thing.
  • The device watches for a momentary short on all pins (by the leading edge of the plug) to detect plug insertion/removal.
  • The pins on the plug are deactivated until after the plug is fully inserted, when a wake-up signal on one of the pins cues the chip inside the plug. This avoids any shorting hazard while the plug isn’t inside the connector.
  • The controller/driver chip tells the device what type it is, and for cases like the Lightning-to-USB cable whether a charger (that sends power) or a device (that needs power) is on the other end.
  • The device can then switch the other pins between the SoC’s data lines or the power circuitry, as needed in each case.
  • Once everything is properly set up, the controller/driver chip gets digital signals from the SoC and converts them – via serial/parallel, ADC/DAC, differential drivers or whatever – to whatever is needed by the interface on the other end of the adapter or cable.
Copied without permission from Wiki.
Martin
 
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