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USB chargers are one of the most popular things to build here on Instructables. However countless people have been disappointed to find out that after all of their hard work, their iPods just sit there and do nothing, despite receiving 5V.

Recently my USB car charger died. I thought it'd be great if I could just install USB ports into the center console, and I totally did too. But the iPod wouldn't charge, so I scoured the internet looking for an answer. I found out what I needed to do was put resistors onto the data lines, but nobody agreed on what resistors or even how to hook them up. Finally I just ripped apart my broken USB charger to see how they did it.

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## Step 1: Schematics

First off I should mention that this is supplemental Instructable to the countless others that show you how to build a USB charger. I am assuming you've already made something that can supply 5 volts DC. I assume no responsibility for how this jives with your 5V power supply or the USB devices you connect to it. All I really know for certain is it works perfectly with my 4G iPod, my Energizer USB-powered battery charger, and my cellphone.

OK, here we go.

The values of the resistors in the schematic below can be approximate. Those are just the values I measured from the resistors on my dead car charger. You could also hook up different valued resistors in series to dial in the exact ohms (22K + 22K = 44K, perfect for R2.) Also, 1/8W resistors will work just fine.

Once you build the circuit, test it. You should get around 2.7 volts out of D- and 2V out of D+. This may seem scary high but it's in the USB spec for signaling a USB 2.0 connection. This is how the iPod knows it's OK to draw the power it needs to charge.

## Step 2: Conclusion

Well, that's pretty much it. It seems simple but I had to go to a lot of trouble to figure this all out.

Feel free to use any images or designs in your own Instructable or whatever. Just give me credit. Also feel free to criticize any aspect of my circuit designs. The configuration and values of the resistors came from a Griffin iPod USB charger that I bought from the Apple store, and I lifted a good deal of the power supply schematics from ranjeevm in this Instructable.

June 18th, 2009: This project will work for the 2nd Generation iPod Touch or any version of the iPhone 3G. However those devices need a very precise 5 volts to sucessfully charge. You may find that simply buying an official charger or battery from ebay or something may save you a lot of frustration.

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## 111 Discussions

thanks a lot.But LM7805 can handle 1A . This mean ur charger is very slow charging .Right?

No, actually a LM7805 is able to draw 1,5 A. but with an heatsink you can draw a bit more, and Actual official chargers are 1A For iPod/iPhone and 2.1A. For iPads

Cheers for this, I've been getting a bit fed up with other Instructables saying you only need to connect the red and black to charge an iPhone. Bodging an Iphone charging dock into a running machine is tricky enough (already had to replace a processor chip that i blew, gotta love eBay
Although i did use a 2x 33k a 22k and 47k resistor setup as i had the parts already. love the way that every version of this I've seen uses different resistor values.

2 replies

to help guys looking for this.

forget about the value of the resistors for a minute.

what you need is a voltage divider to get 2.8v on d+ and 2on d- etc

the reason why the resistor values are all different is because you can use different resistors and people either use what they have to hand or can easily get there hands on

to help guys looking for this.

forget about the value of the resistors for a minute.

what you need is a voltage divider to get 2.8v on d+ and 2on d- etc

the reason why the resistor values are all different is because you can use different resistors and people either use what they have to hand or can easily get there hands on

I made this and it worked great with my iPhone 5S... But it didn't work with my friend's iPhone 4S. I suspect that the required voltages on the data lines are different. A further analysis is required.

The black goes to your ground, the red goes to the positive on your 5V power supply. You will need to hook up the R2/R1 voltage divider to white, and R3/R1 to green.

Thank you!

Hmmm.... actually, I think I did come across an Instructable that mentioned you need to trick your device into charging by supplying some voltage to the data line... don't quote me, though!

At my school we make a rechargeable LED Torch (http://www.scorpiotechnology.com.au/assets/technology_catalogue.pdf). We have a number of gearboxes left over from unfinished projects over the years. I have been toying with the idea of making a rechargeable USB charger. My circuit design is below as well as a Circuit Wizard file. It seems that the batteries could be replaced with any combination above 7 Volts. The Lithium Ion batteries I am planning on using are 40mA each, so four would provide 160mA (when not winding), but this falls well below the 1A required for modern usb devices. From what I gather rechargeable 3.6 Volt 1/2R6 batteries are rated at 700mA, two of these would provide 1400mA, well over the required 1A for charging a usb device. If I were to use AA or AAA at 1.5 Volts each I would need at least 5 to provide the 7 Volts that the LM7805 requires.