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[on:]

I am in middle on trying to assemble a kegbot and I am going to be using an Arduino to communicate with two Swiss flow sensors to monitor beer.  I am also going to be interfacing a iPod Touch 2G through a protoshield to the Arduino.  I have spent the past few days researching iDevice charging, and I feel I have a good understanding of the topic, and I also feel I have a basic understanding of power supplies, and what the Arduino is capable of.

Basically I would like to be able to charge the iPod Touch 2G from the Arduino with out having to use a AC plug to USB adapter to get power to the iPod Touch.  I assembled an AC adapter the other day for the Arduino, and the specs are as follows:

INPUT: 120VAC 60Hz 21.6W
OUTPUT: 12VDC 850mA

Now, I understand from watching this video that the iPod Touch 2G, iPhone 3G(S) require precise voltages in order to charge from different power sources.  If a late iDevice (one of three described above) is plugged into a USB port of a computer, the computer can only provide 500mA (USB spec), and the voltages traveling across the data pins (D+ and D-) of the USB port/cable have to be 2.0VDC, but if the device is charging from the MB352LL using 1A, then the voltages need to be 2.8VDC on D- and 2.0VDC on D+.  I am totally content with providing the iPod Touch 500mA using the Arduino, but I understand that the digital out pins can only provide 40mA of current for each pin.  So is there some way I can make sure I can provide a steady 500mA to the iPod Touch using a pass through from the Arduino AC power source of some sort?

[Reply #1 on:]

Do you need to switch the charging on and off?  If not you could run the Vcc to the device but that's putting a lot of power through the Arduino regulator (3.5 watts - much more than it can handle).

So you will need a separate regulator with moderate/large heat sink to pass 5V 0.5A to the device.  The control voltages may be generated with voltage divider to the D+ and D- pins - assuming they don't draw significant current.

[Reply #2 on:]

Do you need to switch the charging on and off?  If not you could run the Vcc to the device but that's putting a lot of power through the Arduino regulator (3.5 watts - much more than it can handle).

So you will need a separate regulator with moderate/large heat sink to pass 5V 0.5A to the device.  The control voltages may be generated with voltage divider to the D+ and D- pins - assuming they don't draw significant current.

Okay, so looking at the Arduino Duemilanove I see the Vin pin on the lower portion of the PCB below the big ATMEGA 328 chip.  Could I use some sort of electronic device to dial in the proper voltage need to charge the iPod Touch.

As for charging and use, the newer devices are able to draw power from the battery, and charge the battery simultaneously from what I understand because USB cables provide four wires, and two of the wires provide a steady 5VDC @ 500mA while the D+ and D- can provide a steady 2VDC (powered off a USB port) to charge the battery while the device is in use.  So as long as everything is hooked up and powered on the device will be drawing current from the Arduino to keep the battery charged.

As for the voltage divider to provide the proper current/voltage for the iPod Touch there are two schematics listed on this site, which provide a voltage divider for both a 1A source and a 500mA source.  I just need to figure out how to get a 5VDC draw @ 500mA from the Vin

[Reply #3 on:]

woah woah, the D+ and D- are for signalling use only. you wont get any power off those lines. it can recharge and stay powered because... well, thats how they designed their circuit. power the main board first, then use extra current to pump into the battery.

[Reply #4 on:]

woah woah, the D+ and D- are for signalling use only. you wont get any power off those lines. it can recharge and stay powered because... well, thats how they designed their circuit. power the main board first, then use extra current to pump into the battery.

Yeah I understand from USB spec that voltage isn't supposed to be transmitted over D+ and D- but Apple didn't conform to USB spec with the newer devices :-/  That's how I understand it at the moment.  If you watch the video stated above in the post the lady in the video does a good job explaining iDevice charging.

[Reply #5 on:]

I am in middle on trying to assemble aipad case and I am going to be using an Arduino to communicate with two Swiss flow sensors to monitor beer.  I am also going to be interfacing a iPod Touch 2G through a protoshield to the Arduino.  I have spent the past few days researching iDevice charging, and I feel I have a good understanding of the topic, and I also feel I have a basic understanding of power supplies, and what the Arduino is capable of.

Basically I would like to be able to charge the iPod Touch 2G from the Arduino with out having to use a iPad2 case to get power to the iPod Touch.  Iipad 2 casethe other day for the Arduino, and the specs are as follows:

INPUT: 120VAC 60Hz 21.6W
OUTPUT: 12VDC 850mA

Now, I understand from watching that the iPod Touch 2G, iPhone 3G(S) require precise voltages in order to charge from different power sources.  If a late iDevice (one of three described above) is plugged into a USB port of a computer, the computer can only provide 500mA (USB spec), and the voltages traveling across the data pins (D+ and D-) of the USB port/cable have to be 2.0VDC, but if the device is charging from the using 1A, then the voltages need to be 2.8VDC on D- and 2.0VDC on D+.  I am totally content with providing the iPod Touch 500mA using the Arduino, but I understand that the digital out pins can only provide 40mA of current for each pin.  So is there some way I can make sure I can provide a steady 500mA to the iPod Touch using a pass through from the Arduino AC power source of some sort?

you wont get any power off those lines. it can recharge and stay powered because... well, thats how they designed their circuit. power the main board first, then use extra current to pump into the battery.

[Reply #6 on:]

Yeah I understand from USB spec that voltage isn't supposed to be transmitted over D+ and D- but Apple didn't conform to USB spec with the newer devices :-/  That's how I understand it at the moment.  If you watch the video stated above in the post the lady in the video does a good job explaining iDevice charging

Then you need to watch the movie again, because this is not the case.  The D+ and D- lines have sense resistors built into them so that iDevices can determine which charger is connected to them.  This has nothing to do with power being available on D+ and D-.  This method is NOT a violation of the USB spec.  Other manufacturers use similar techniques to determine if their device is connected to an active USB port or just a power port.  Apple took it one step further.

This method will cause different voltages to appear on D+ and D-, but do not confuse "power" with "voltage."  These are very different (but related) things.  Also, voltage is never "transmitted."