Carl Hutzler's Blog

Every summer there is a great festival in Baltimore called Artscape. The festival is located next to the Maryland Institute College of Art, the symphony and several other artsy attractions in the city. Lots of music, local artisans, food, beer and fun stuff for kids. This year I went with my kids for the first time in maybe a decade and we had a lot of fun seeing the band CAKE and playing with hoola hoops and more. This image sums it up for me :-)

*** Be WARNED. If you try this and fry your iPod/iPhone, don’t come crying to me! **

** Do this at your own risk **

My family has an ever growing iPod/iPhone collection. It is actually sad in a way, but it is what it is. We currently have three iPhones – First gen, 3G and 3GS. And we have a first gen iPod Touch.

When we go on vacation or a trip to visit my parents, we bring along a charger but the issue is that with four devices, someone is always needing a charge at the same time as someone else.

So I started playing around with USB hubs. Given that a simple 4 port USB hub that has an external power supply can supply 500mA to each USB port, I figured I could easily charge four devices. Not so as I would quickly find out. Most iPods and iPhones will not simply charge when they are connected to a USB port UNLESS that USB port is directly or indirectly connected to a computer.

From what now seems like endless experimentation, I have found a solution. To trick the iPhone/iPod into thinking it is connected to something it can charge from, you simply short the USB Data+ and Data- pins together. So basically if you provide 5V and GND on pins 1 and 4 and short the middle two pins, many iPods/iPhones will charge. I have tested the following:

iPhone 3GS – charges
iPhone 3G – charges
iPhone First Gen – charges

iPod 30G 5th Gen – charges
iPod Nano 3rd gen (the sort of square one and the first with video) – DOES NOT CHARGE
iPod Shuffle (2nd gen square shape with buttons) – DOES NOT CHARGE

So if you have a newer iPod or iPhone, chances are that my method will work for you. And if you have an old hub (USB 1.1 is just fine) that allows for external power (and you have the power adapter), you might give this a whirl… (click any image to enlarge)

1) Open up the hub.

2) Find the circuit traces for the middle two pins on the USB ports (Data+ and Data-). Using a dremel, screwdriver or whatever, cut through the traces so that these pins are isolated from the USB hub circuitry. ( Note: the USB hub will never work as a hub again)

3) Solder the middle two USB pins together (Data+ and Data-) so they are just shorted (no voltage on them)

Re-assemble the hub and test with your favorite iPhone/iPod.

I think the reason this works is that the USB charging spec has a way for a USB port to tell a device that it can charge or that it is a charger. While there are several ways to do this and the chip inside the device seems to have some sort of role as well, one of the ways is simply shorting the Data- and Data+ together. I discovered this by accident but later have confirmed on some forums that this may be the reason this works. And perhaps earlier iPods did not sense this while later units did.

One other note… it seems that to charge the last gen iPod Nano (first with video) and the iPod shuffle (2nd gen square shape with buttons) and everything else in the iPod/iPhone line you need to put USB Data+ and Data- at some voltage….many people on the forums claim 2.5V for each or 2.0V for one and 2.8V for the other, etc will work. And from my testing that seems to be the case. So if you want to really have a universal charger for every iPod and iPhone, you would have to go to the trouble to solder in a simple voltage divider into the USB hub. A pair of 330Kohm resistors, in series between 5V and GND would do it. Then solder the junction where the resistors meet (2.5V) to USB Data+ and Data-. That would do it. And I may do this someday, but for now, since the newer iPod/iPhone units seem to like a simply short, and since I am lazy, well, that is the way I will leave it.

And a final note…in my testing I found that the iPhone 3GS drained about 600mA while it was doing a “lot of work” like charging a fairly dead battery (20% life left), streaming a 64kbps radio stream over 3G and with the brightness full up. So while the hub will provide 500mA, it may not be enough to keep the device going non-stop under these conditions. For a solution to that issue, you would have to design your own power supply or buy one I guess. a 1A supply should be enough and that is what Apple’s own power supply is rated for….although I never saw it providing that much in my testing.

Addition: I can now say that a simple voltage divider which gives about 2.5V on the Data+ and Data- pins will get the iPod Nano to charge (the suqareish nano and first that supported video). But strangely, the iPod shuffle 2nd gen will still not charge. Hmmm.

*** Be WARNED. If you try this and fry your iPod/iPhone, don’t come crying to me! **

** Do this at your own risk **

Recently I ranted about how Apple has changed their dock connector numerous times to render old accessories useless. And while some of it seems to be necessary as I explained, other changes seem like greed.

Anyway, in my continuing saga to understand how to do simple things like get “line out” to work, I spent 6 hours over two weekends figuring out how to simply charge my iPhone 3G in the car. And this issue also affects the 3GS and most of the newest iPod Touch 2G and likely the latest Nano.

Basically, you can not simply use a standard Apple USB cable (30 pin dock connector on one end, USB on the other) to charge one of these things anymore unless it is connected to a computer. So take a standard car cigarette lighter adapter with a USB connector on it. These are commonly available for a couple of bucks and very convenient as they can charge more and more things that simply take 5V on a USB connector – blackberry’s, GPS, Jawbone headsets and more. But it won’t work with an iPhone.

Why? Well it seems a bit complicated to me, but I think I understand it. Basically the iPhone needs to know if it is connected to a computer’s USB port (limit of 500mA) or a regular wall charger (some are limited to an amp or even more). This way it “knows” how much current it can draw from the connector.

Now there are a lot of discussions in the forums about using a voltage divider network (two resistors between V+ and GND) to create +2.8V and another two resistors to create +2.0V for the USB Data- and Data+ pins, respectively. If these voltages are set on the DATA- and DATA+ pins, the iPhone will charge. And I found this to be true. In fact, the Apple wall charger has exactly those voltages on those pins which is likely where everyone got the idea.

But from playing around with it, I found that you could set both of these pins to the same voltage as long as it was above maybe 2.0V which makes it a little easier for the voltage divider network….now you just need one set of resistors – maybe 33K and 33K to give you +2.5V on Data- and Data+.

But I later found through more experimenting that simply shorting Data+ and Data- together (no voltage…just a solder joint), would cause the iPhone 3G, 3GS, last gen Nano, iPhone 2G, iPod 5G and likely many more to charge. I tested them all. They all work.

So again, all you seem to need is a standard USB port which supplies 5V on pin 1, GND on pin 4 and pins 2 and 3 (Data+ and Data-) soldered together.

I took a cheap USB charger like this one which runs $3 on sale. I opened it up, soldered the middle two connectors on the USB jack together, and viola!

So if you have an old charger laying around and your iPhone says “not compatible” you may be able to make it work. Keep in mind though that some old chargers output 12VDC (not 5VDC). These will not work with the newer iPhones/iPods because they no longer have the ability to charge from a “firewire” 12VDC input anymore. But if you are sure you have 5VDC and it still won’t charge, try soldering the middle two USB pins together and you should be happy.