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MintyBoost Fundamental
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MintyBoost Fundamental

by Compass on Thu Jan 24, 2013 1:04 am

Hello:

I recently purchased an Iphone 5, and been thinking about a small portable field charger for it when I do not have access to an outlet, or computer for the USB port.

Before finding Adafruit, and coming across the MintyBoost, I started to rig up my own portable charger using the following:

http://www.hobbyking.com/hobbyking/stor ... duct=28650

A two cell LiFEPo battery pack which is a safer chemistry than a Lithium Polymer battery, and wire it up to this:

http://www.hobbyking.com/hobbyking/stor ... duct=28248

Voltage regulator which takes 6-23v input to a 5.1v out. I use these to power my servos and receiver separately in my model aircraft.
I cut up and spliced a sacrifical USB cable and simply soldered the power connections and left the two data wires floating.
See photo attached. The thing with the checkerboard was the battery. I took it apart and broke it down to two 3.3v single cells for use with the Mintyboost.

After rigging it up (I have not connected it to the iphone yet), I came across Adafruit and read about the Mintyboost.

Please confirm/correct my understanding as it applies for iphones (iphone 5 specifically):

As a way to ensure the use of Apple only products, they put a voltage divider to the two data pins on the USB connector. If the iphone does not sense a 2 volt (or thereabouts) potential across the two data lines, the iphone will not/should not charge correct?

The iphone obviously charges fine when I plug the lightening cable into the usb port of my computer.
Also, when I purchased this: http://www.bhphotovideo.com/bnh/control ... &A=details
And plug it into my carport, it also charges my iphone just fine.

In order for the MintyBoost to work, it requires a voltage divider on the data pins...why? How does the iphone know the difference between a usb connection to a computer, a car-port-to-usb, or a lithium battery-to-usb setup like the attached photo, or a pre-version 3 MintyBoost?

What am I missing?

Thanks,
Compass
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Compass
 
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Re: MintyBoost Fundamental

by adafruit_support_bill on Thu Jan 24, 2013 7:38 am

The iPhone 5 and most current generation phones appear to adhere to the new charging standard which calls for D+/D- to be shorted together. There is a good summary of the charging protocols here: http://en.wikipedia.org/wiki/Universal_Serial_Bus
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Re: MintyBoost Fundamental

by Compass on Sat Jan 26, 2013 8:31 pm

From the Wiki:
When D+ = D- = 2V, the device may pull up to 500 mA. When D+ = 2.0 V and D- = 2.8 V, the device may pull up to 1000 mA of current.

I finished putting the MintyBoost together, everything checks out ok, 5v across the power leads, and 2v across the D+ & D-. Works fine on my iphone 5. I did not need to short the two data wires.

So the iphone is looking for a resistor signal (D+ & D- = 2.0 volts in this case) in order to provide a current up to 500ma.

Question is...when I plug into a computer usb, or a car adapter to usb like the Griffin in the first post, it works. There is no resistor signal, no shorted data pins, yet it works. Why?

Is there a feature whereby the iphone can detect what is essentially a large capacity power source such as a cpu power supply, ac to dc apple wall adapter, 12 volt car battery, and bypasses this resistor signal?

Just trying to understand.

Thanks,
Compass
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Re: MintyBoost Fundamental

by adafruit_support_bill on Sun Jan 27, 2013 8:29 am

For the computer USB port, the phone will 'talk' over the data lines to figure out what it is connected to and negotiate a charge rate. If the thing doesn't 'talk' then it looks for the voltage levels and goes by that. Most car chargers and wall chargers these days have a resistor network built in for that purpose.
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