A few weeks ago I managed to use the motor to charge a mini speaker. This is because speakers are very simple USB connections that only require power going in (5V which I supplied using a 5V regulator) and ground coming out.


However, to charge an iPhone it is more complicated. Apple do not want you to easily be able to build your own charger (whether this is actually for safety or perhaps a part of the bigger picture in reducing our self sufficiency one can only speculate) so they’ve included extra criteria before the device will begin to draw current. I learnt through the two videos below, and Adafruit’s tutorial on iCharging that the input into the other two cables on a USB adaptor is very important.

Reverse engineering Apple’s secret charging methods from adafruit industries on Vimeo.

For the device to think that it is connected to a wall socket, and therefore draw 1.0Amps of current (making 5Watts at 5V charging – a quick charge) you need to supply data connection D- with 2.0V and D+ 2.8V.

For the device to think that it is connected to a computer USB, and therefore draw 0.5Amps of current (making 2.5Watts at 5V charging – a slow charge) you need to supply the data connection D- with 2.0V and D+ with also 2.0V.

I decided to test this using a USB backup charger and a multimeter and discovered, perhaps a little inconsistently, that the two middle connections were providing 2.0V.


In the videos above, they had used resistors to divide the voltage down to the 2.0V, however I decided to use a switching voltage regulator with an adjustable drop.


I attached it to the battery of an electric screwdriver through lack of being able to think of anything else that would provide me with over 7V to set up the regulator. It took a long time to find the twist on the screw that actually made a difference, but after nearly giving up, the voltage started to drop to 2.0V.


I then added this onto my existing circuit. I was unsure where to connect the ground coming out of the regulator, as my USB inputs were only inputs, but then I realised that I would also connect it to the same ground of the rest of the circuit, the ground coming out of the USB.


Next, it was time to make the really scary jump to actually plugging my iPhone in. I first tested it with a camera battery providing just under 7V at a steady level (I knew the fluctuating current generation of my motor would add another element into the mix).


And it worked!

Seeing my phone screen light up was so exciting!


Leave a Reply