Device charger improvements

Charging Apple products

Because of the way Apple devices are made, you will need to add a voltage to the data pins for it to be able to charge the device.

We found this post by Voltaic System that makes battery backs which describe the voltages needed to charge Apple device under different conditions. For our device charger we decided on using the D- = 2.0V and D+ = 2.75V configuration.

  1. You will need to use a couple of 10 turn potentiometers using the following schematic and mounting it near the terminal block.
  2. Solder wires to the D- and D+ points on the USB breakouts and wire them into a common point and screw them into the screw terminal making sure to connect D- to the D- wires and D+ to D+
  3. Connect the wires from the 5 volt and ground and connect them to the other screw terminal again confirming 5 volt to 5 volt and ground to ground
  4. Turn on the power, make sure no devices are attached, and adjust the potentiometers to get the correct values on D+ and D-
  5. Confirm that the voltages are correct across the USB ports before connecting any devices

Voltage divider schematic

Future improvements and modifications

We ultimately ended up not applying any finish to the charger but we had some thoughts on what could be done and thought we would share them.

Applying a simple wood varnish or stain would have helped remove the smell of burned wood from the laser cutting process as well as giving the device charger a less rough look.

Adding two USB 3.0 - USB Hub 4-ports will make it possible to access all of the connected devices easily which is very useful if you use the devices for app development. All you need to do is connect the data pins from the breakout board to the hub as well as the ground pin to the V- on the power supply so that you have common ground. This should also provide the voltage required for Apple device to recognize the device charger. Now either make a hole to pull the USB cable through or add a USB panel mount like these:

Switchcraft USB B to A Panel Mount USB 2.0 B Female Socket Panel Mount To B Male

Adding a Raspberry Pi together with the USB hub will allow you to SSH into the R-Pi and run ADB commands directly to all of the attached devices. Which would provide an Android developer with many possibilities. This could for example be the small and cheap Raspberry Pi Zero.

By: Rune Haugaard