Overview

This is a charger I built for my iPod. The day I got my iPod I opted not to use iTunes or the default iPod software, instead i flashed its firmware and installed rockbox on it. Its a great replacement if you feel you don’t want to get caught in the default Apple software twist. The only problem I had was when charging, when I turn the computer off the iPod would stay on and run flat (rockbox has a new version but I’m not entirely sure if they fixed this yet). So my solution was to build my own charger that can stay on that is not dependant on the computer. Here follows my solution.

The basic idea

Most electronic devices only need a constant power supply and the correct adapter to charge correctly. Your cellphone charger is nothing more than a DC power supply, and the iPod wall chargers one buys from the apple store is no different.

I know for a fact it charged from 5 Volts (its the voltage a USB port delivers), i connected the iPod to my power supply and measured the current consumed. It was exactly 0.1 Ampere. Now I knew what I had to design for so the next stage was building the power supply for the charger.

The Design

I used components that I had laying around the house, the power supply absolutely does not need to be exactly the same as mine. As long as it delivers 100mA at 5V it should be fine.

Required components

• 1000 uF 16V capacitor
• 5V 100mA regulator (78L05)
• Center tap transformer with 9V-0-9V ~ 300mA output
• 2 Diodes (1N4007)
• USB to PS2 converter OR USB extension cable

Circuit diagram

Building the charger

Connecting the transformer to mains

I used a power cable from broken speakers for my project. A nice little lesson learned from this project was that stripping the wires at the same lengths can have disastrous effects, no matter how nice your insulation tape seems. Lets just say burning plastic flew all over the room. So to avoid disappointment in the future cut the wires as shown below:

For some reason when I cut my cables at the same length they created a short circuit through my insulation tape. I was quite surprised to say the least. When cutting it at different lengths you ensure that something similar does not happen with you. Depending on the cable you are using you may have a wire with green and yellow stripes, just cut it off as close to the main insulation (the black insulation in the picture) with as little as possible copper sticking out and insulate with tape. The brown and blue wires of the cable are the two that gets connected to the transformer.

WARNING: Please ensure you connect the transformer the correct way round. If its connected backwards, instead of stepping down voltage, it steps up voltage. Instead of a Voltage of 240 V stepped down to 9 V (about a 24 times reduction) it can step up the voltage to something in the range of 5000 Volts. I don’t need to tell you this extremely dangerous.

Diodes for wave rectification

If you have a center-tap transformer you can use the configuration shown in the circuit diagram above. Each diode does half wave rectification. When added together you get a fully rectified wave.

For a normal transformer use a diode bridge circuit to achieve full wave rectification (shown below).

Capacitor

The Capacitor removes ripple from the fully rectified wave. For 100mA a 1000uF capacitor should be more than enough. Make sure the voltage rating on the capacitor is about 1.5 to 2 times more than that of the transformer output.

Voltage regulator

I used the 78L05 voltage regulator. Its is capable of a 100mA 5V output. For instruction on connecting view the 78L05 datasheet. Just remember the picture shown with the pin-outs is a bottom view.

Connecting to the USB adapter

USB adapters have the following pinout:

• pin1: VCC (5 Volt)
• pin2: Data -
• pin3: Data +
• pin4: Ground

A useful website for pin-outs are pinouts.ru. We use the controller USB pin-outs since we want to mimic the USB hub (the controller pin-outs are shown on the top right). I used an old PS2toUSB converter to get the needed USB controller mounting, if you cannot find one a USB extension cable will work as well.

The ps2 to usb converter I used

The stripped converter

The usuable parts

When viewing the converter from the USB side, with the copper pieces at the top, pin 1 is on the left and pin 4 is on the right. Pin 1 should be connected to the 5V output, and pins 2,3 (data) and 4 to Ground. If you leave pins 2, and 3 floating your iPod might not correctly go into charging mode.

The final result!

And here is the end result, busy charging my iPod! Full size