A USB condom is to safely be able to charge your devices from unknown power sources, for example someones computer or any unknown outlet. The reason why it's needed is that with the I/O connections it is possible to infect and read/write without permission to your device.
It can also be used when someone want to use a USB-port on your computer for charging. Using a condom such as this makes it impossible to compromise your computer.
My design goal was to make it as small as possible yet being sturdy and very easy to print without supports. Being only one part it is extremely easy to assemble.
- Print the case without support
- Cut out a 10x30mm from a strip board with four traces
- Solder a USB A pcb connector onto the strip board
- You might have to trim off metal clamps etc from the connector
- Solder voltage dividers (on Android an 100 ohm resistor between D- & D+ is enough)
- Remove the two inner traces except area where pins are soldered
- Push connector into the case, trim if needed, it should be a snug fit
- Fill the empty space under the connector with hot glue
NOTE: In order to make it possible to charge more then 500mA the middle traces need to be connected with a 100ohm resistor. For iPhone it is a bit more complicated. Voltage dividers need to be added to D- and D+, see circuit picture.
I've made two variants, one shorter and one longer, the longer variant fits the voltage dividers using 0.25W resistors.
WARNING: Do not use the variant with the voltage dividers for charging off a standard USB-port on a computer since these are rated for only 500mA. It might work but you've been warned.