I am planning a project very similar to the one seen in the following gallery. (https://i.sstatic.net/FMecg.jpg) I like the idea of having my phone plugged into the same unit for charging. My only concern is I only want to have one power cable being attached. The power cable needs to power both an Arduino Micro, some LEDs, and charge the phone, so I will likely be using a 5V wall wart or something similar (high enough power rating).

My big concern is making sure the battery is charged properly and is not over charged. I don't want to just plug it into a constant 5V-1A circuit, and ruin the battery. I have seen a few charging circuits online (like this one), but did not know if this was a safe option.

Any suggestions would be greatly appreciated. I am looking for a package that is relatively easy to use/solder and is reliable/safe. There are plenty of charging circuits, but are not exactly user friendly for small-ish hobby projects.

For what its worth, it is an iPhone 6 that needs to be charged, so it is a 3.8V 1800mAh lithium ion battery.

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    \$\begingroup\$ The phone charges the battery, not the supply. If the battery becomes damaged then it's the phone's fault. \$\endgroup\$ Commented Jan 26, 2016 at 17:08
  • \$\begingroup\$ @IgnacioVazquez-Abrams Doesn't the standard USB brick have some charging circuitry in it as well? That is what I was concerned about since I will not be using that standard little white plug box. \$\endgroup\$ Commented Jan 26, 2016 at 17:15
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    \$\begingroup\$ USB just has a 5V supply. There may be some negotiation in which a device asks for permission to draw more than a certain amount of current and waits for it to be granted, but there is no battery charger in a USB supply, just straight 5V. \$\endgroup\$ Commented Jan 26, 2016 at 17:27
  • \$\begingroup\$ ok, sounds good to me then. I just wanted to be sure before I ruined my phone. A simple stupid question versus several hundred dollars in ruined electronics is a good trade off to me. \$\endgroup\$ Commented Jan 26, 2016 at 17:40

1 Answer 1


Charging lithium batteries is handled by the charging circuit found inside your phone , this circuit handles undervoltage and overvoltage protection of the lithium battery for safety concerns and battery life.

The charger you plug into the wall ( AC mains ) contains mainly a transofrmer and rectifing diodes.

So simply plug 5v into the phone is safe and no need for any circuit. you can just use usb connector and connect only the power pins leave everythng unconnected and you are good to go.

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    \$\begingroup\$ You can't just leave data pins disconnected for many phones now, you need the resistors across the data pins to indicate how much is safe to draw. Look at this page for more info: learn.adafruit.com/minty-boost/icharging \$\endgroup\$ Commented Jan 26, 2016 at 19:10
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    \$\begingroup\$ if you short the d+ and d- ( pin 2 and 3) you will get fast charging , that is what i have tried . but good point you provided. thanks \$\endgroup\$
    – ElectronS
    Commented Feb 12, 2016 at 10:00

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