iDevice – USB charging 3G(S)/iPod Touch 2G using resistors

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iDevice – USB charging 3G(S)/iPod Touch 2G using resistors

Postby ipatch » March 7th, 2011, 11:40 pm

Alright, I am trying to figure out how I can charge my iDevice (iPod Touch 2G) using the resistor method provided here. The page states:

To charge an iPhone 3G / iPod Touch 2nd gen, usb data- (25) should be at 2.8v, <br /> usb data+(27) should be at 2.0v. This can be done with a few simple resistors: 33k to +5v (23) and 22k to gnd(16) to obtain 2v and 33k to +5v and 47k to gnd to obtain 2.8v. This is a notification to the iphone that it is connected to the external charger and may drain amps from the usb.



I don't know who decided to green light these instructions, but needless to say, they SUCK, at least in my little book. Here is a picture of what I am trying to achieve, hopefully someone can enlighten me on this situation. I posted this same thread/question on my blog here and figured one of the many intelligent people on this forum can help me solve my problem.

*UPDATE*

There is an error in my picture, and if I read correctly the white wire should be going to pin 27.

Image
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby st2000 » March 8th, 2011, 12:10 am

I know you don't want to hear this, but the directions sound complete to me. Also, if you read them carefully you will see you need two 33,000 ohm resisters. Which is a total of four resisters. I think these directions came from adafruit.com. Do be careful making this adapter. I am not sure what would happen if you shorted one of the data lines to ground or +5. I think this circuit depends on you supplying USB charging voltage on the proper pins. That is 5 volts on the proper pin. There are some (many) iPod devices which still only supply FireWire charging voltages. That is 12 volts on a different pin. These types of devices will not charge newer iPods like a Touch with out an adapter.

The instructions say:
"usb data- (25) should be at 2.8v"
"33k to +5v and 47k to gnd to obtain 2.8v"
-and-
"usb data+(27) should be at 2.0v"
"33k to +5v (23) and 22k to gnd (16) to obtain 2v"

So 33K to pins 23 & 25 & 47K to pins 16 & 25.

And 33K to pins 23 & 27 & 22K to pins 16 & 27.

1) Do this at your own risk. I looked over this follow up but sill can not be sure there are no errors. Consider there are commercial products that can do this which probably cost less than that break out board you bought from sparkfun.com.

2) If I were you I wouldn't plug my $300 iPod Touch into this thing until after I checked the voltages on all the pins. Especially the Data + and Data - pins. This assuming the source of all this secret Apple voltage information is in fact correct.

-good luck
Last edited by st2000 on March 10th, 2011, 11:42 pm, edited 1 time in total.
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby error404 » March 8th, 2011, 12:12 am

Goddamn Apple. There is a USB specification for this (though it is relatively new). It specifies that D+ and D- should be shorted to indicate a charger. That's it. Phone them and bitch at them for not following the specification.

According to here: http://www.ladyada.net/make/mintyboost/icharge.html all you really need to do is put both data lines at ~2.0V, which makes it a little easier.

Pretty straightforward. Solder the 33K resistor to the 22K resistor. The midpoint goes to the data line, the 33K unconnected side goes to +5V, the 22K unconnected side goes to GND. Make two of these.
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby ipatch » March 10th, 2011, 8:04 pm

error404 wrote:Goddamn Apple. There is a USB specification for this (though it is relatively new). It specifies that D+ and D- should be shorted to indicate a charger. That's it. Phone them and bitch at them for not following the specification.

According to here: http://www.ladyada.net/make/mintyboost/icharge.html all you really need to do is put both data lines at ~2.0V, which makes it a little easier.

Pretty straightforward. Solder the 33K resistor to the 22K resistor. The midpoint goes to the data line, the 33K unconnected side goes to +5V, the 22K unconnected side goes to GND. Make two of these.



Alright, so forgive if I did not setup this up correctly using my breadboard as I have never breadboarded a circuit before. I setup a test circuit seen below, but I am still not getting the voltage required to charge the iPod Touch 2G. The multimeter (Fluke 116) does not show any voltage on D+ or D- when I setup this circuit. Hopefully there is just something wrong with the wiring of my breadboard.

Image
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby oPossum » March 10th, 2011, 8:22 pm

Using 5% resistor values...

Image

Using 1% resistor values...

Image
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby ipatch » March 10th, 2011, 8:26 pm

So I started checking the voltage coming off D+ and D- and I wasn't even getting close to 5VDC on the white wire (D+) so there was an obvious bad connection coming out of the breadboard. ...learning slowly but surely (sighs)
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby error404 » March 10th, 2011, 9:22 pm

I think your breadboard looks correct, but it's tough to tell from that photo. It should be like this (excuse the error, I wanted the input on the left, but I wasn't about to redraw it!):
Image

The voltage is the same on both pins so I don't think you should need more than 1 divider. If it doesn't work, just don't connect D- and D+ and give both the same divider.
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby ipatch » March 10th, 2011, 10:23 pm

error404 wrote:I think your breadboard looks correct, but it's tough to tell from that photo. It should be like this (excuse the error, I wanted the input on the left, but I wasn't about to redraw it!):

No need to double post picture

The voltage is the same on both pins so I don't think you should need more than 1 divider. If it doesn't work, just don't connect D- and D+ and give both the same divider.


Hey with your two resistor setup I am getting 2 VDC on D+ and 3 VDC on D- The iPod screen turned on when I plugged it in, but there was no indication of charging. I really appreciate the help and the effort put into drawing the picture.
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Re: iDevice – USB charging 3G(S)/iPod Touch 2G using resisto

Postby ipatch » March 10th, 2011, 11:11 pm

Alright, so I watched this video AGAIN, and I decided to pay attention this time. If one wants to charge an iDevice such an iPhone 3G(S) via USB (500 mA) one needs to have the voltage of both data lines (D+ D-) ~ set to 2VDC in order for charging of the device to happen.
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