Articles :: Homebrew portable USB battery charger!

unstable -- Mar 22, 2006

I have just finished putting the final touches o­n an idea I had earlier today...

I am taking a flight to the states this weekend, and want to listen to MP3's o­n my Ipaq for as long as I can during the journey. This made me thing how long my ipaq batter will last when constantly playing MP3's, considering lately it has been dieing o­n me and i have had to restore all my files and settings (Pain in the arse!).

Anywhoo... I came up with the idea of having a square 9v batter in some sort of circuit that will power a USB socket, after all these devices o­nly use the 5v rail from a USB socket to charge and power. So I searched the internet a little and found a copule of people had already made such a device (Mainly for ipods, but they all do the same thing). People have been using Zener diodes to create a 5v supply from a 9v battery, or an array of 1.2v (AA, AAA...) batteries. Well seeing as I have been playing with electronics which need a regulated 5v supply lately, I know a little about the 5v regulator L7805. So, I have designed a circuit which uses the 7805 regulator, a capacitor (have lots of Tant caps laying about), and a few diodes for safety (of my ipaq). Put it all together o­n a test board and it all worked :). But the 7805 regulator wastes the extra power by converting it to heat... not much use for me and a bit crappy when relying o­n a small battery. So I decided to add a toggle switch, which I got from an ebay auction of "Various electronic components...". Together with the switch I needed an LED to show if the circuit was powered or not.

So after a quick trip to Maplin, I had all the bits needed to create my first practical project. Spent the rest of the night building the circuit and carving out the project box. Granted my Drimmel skills arent anything to boast about, but all in all I think I did a satisfactory job (It's not there for it's looks anyway). The o­nly annoying bit was the USB hole is not very square, and the socket is recessed into the box.

Well the glue is now drying, o­nce thats all set I will be giving it a field test to see how well it copes with charging my ipaq, and how long it lasts.

I think I wont be taking it to the states with me after all... I'm sure the airport security wont appreciate a little black box with a big red switch, LED and a few electronics being in my hand luggage... I doubt I would have time to explain myself and it just isnt worth the hassle (Those who know me will already know the hassle surrounding this trip to the states!!!).

I have, as always, posted some pics in the gallery. Link to them from here.

I will try and post circuit diagrams soon but it's pretty obvious where all the components go.