How to build an AC-powered USB charger for toys or other devices by re-purposing an old cell-phone charger.
The USB Charger
I recently bought a very interesting remote controlled helicopter: the Syma S107. This is a really a fun (and affordable) toy to play around with. Unfortunately, the charger that ships with charges through USB . Sounds like a good idea right? Well, after a while this became quite an inconvenience because you have to have a computer ready to be able to charge the device. So what is a "DIYer" supposed to do? Well naturally, I built my own AC charger. I use primarily for charging the helicopter though I reckon it could be used to charge other USB-powered devices.
You will need a basic 5V and at least 500 mA AC adapter. The current rating depends on the device you are going to charge with the adapter, but 500 mA is the "standard" USB current capability (though many PC manufacturers support currents beyond this value). In this case, I used one from an old cell phone rated 5V and 0.7A.
You will also need a female USB connector. I extracted one from an ol USB hub. Older electronics peripherals with USB female connectors could also be used. A bottle cap was used to enclose the uSB connector and the wires. See Figure 1.
Figure 1 - What you will need
First strip out the connector that ships with the cell phone charger. You'll need the positive and the negative wires to connect to a USB female connector. Be sure to measure the output voltage with a multimeter first and verify it's within 5 V ± 5 percent (See Figure 2).
Figure 2- Measuring the output voltage
Extract the female USB connector from the PCB as shown in Figures 3 and 4.
Figure 3 - Extracting the female USB connector with a Dremmel tool
Figure 4 - USN "female" connector
Next you'll solder the two wires to the USB female connector's positive and negative terminals. The USB pinout is quite simple just Google USB connector pin-out and you'll find it. There are four pins. The two pins in the middle are "Data" pins so you don't want to connect to those. The two other pins on each extreme (one on the left, one on the right) connect to the negative and positive supply terminals. To find-out the negative, use your multimeter in continuity mode and find the one that connects to the metal cage in the uSB connector. That's your negative pin. The other extreme, is the positive.
After soldering the connector as shown in Figure 5, you'll need an enclosure to finish the connection and to complete the project. I used a medicine bottle cap and even a coca-cola bottle cap for this purpose.
Finish the project by gluing the PCB to the bottle using a hot glue gun and fill up the spaces with either hot glue or with silicone chalk.
Figure 5 - Soldering the supply wires
Figure 6 - Bottle cap enclosure
Figure 7 - Filling the cap with hot-glue
Figure 8 - Charging the Syma Helicopter
Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com