If you've been following my Macbook 3G entry, you'll know that to get my Vodafone datacard running in the u132 PCMCIA->USB adapter, I need an external power supply - the 5V/500mA supplied by the USB port is not sufficient to get the datacard running with.
My solution up until now has been a standard 6V/1A mains power adapter - clearly not a useful solution for a laptop. I Froogled around and found plenty of portable chargers for mobile phones and similar, but nothing that clearly supported the type of connection that my u132 has.
So, the obvious solution: I make my own.
A power adapter is actually a very simple device - it's basically two things: a power source, and an adapter. But how do I get a portable 6V power source? Easy. I get four 1.5V power sources and connect them together. To spell it out for my less electrical-savvy readers, I use a pack of AA batteries. For the adapter, I just use the changable tip from my existing mains power adapter.
So, the plan is, I get four AA batteries, connect them in series, then connect my adapter tip, and the end result should be a pocket-sized portable power adapter for my u132. Hooray.
If you're thinking "so how is he going to actually connect the batteries up?", then you're thinking similar thoughts to my own, and my answering thoughts were simple: paperclips, Blu-Tack, and/or tinfoil.
Of course, never having done anything like this before, and not entirely trusting my choice of materials, I decided to purchase a (cheap) multimeter to check the electricity was flowing and it was giving the right amount of voltage and current.
The first thing I wanted to do was check the multimeter was working. So after fitting a cheap battery in that and plugging in the two connector things, I turned the dial to Ohms and pressed the connectors against a paperclip. And the needle shot across to indicate that there was little or no resistance.
So, now I have the task of connecting up the batteries. I couldn't find any Blu-Tack so I had to resort to Scotch Magic tape instead. I connected positive to negative on a pair of batteries by simply bridging the terminals with a paperclip and holding in place with the tape.
After testing to confirm this worked, and the new double battery was working as expected, I then repeated this with the other two batteries, and then connected both pairs together using the same method, added some extra tape, and checked my new quad-cell battery to ensure it produced the required six volts.
The easy part out of the way, I now needed to decide how to connect the adapter to the battery.
My first idea was to tape a pair of paperclips to each connection on the adapter, and then connect these paperclips to the ends of the battery. Unfortunately Scotch Magic tape doesn't work very well for this, and it didn't work.
After giving it some proper thought, I decided to attach one connector directly to the positive node, and then I just needed a single paperclip to attach to the negative node. Along with a bit of tin foil to ensure a decent connection, this method was succesful.
We're almost there! Before attaching it I wanted to check everything was still okay, so I checked the voltage and it was just over six volts, all going good.
I booted up my MacBook Pro into Windows, attached the u132 via USB as usual, and then carefully inserted my new home-made portable power adapter into the appropriate slot, and... it worked! As you can just about make out in the photo below, the light is on. :)
And that's it - I have successfully created a pocketable battery-powered adapter for my u132.
But of course the story doesn't end there. As cute as my home-made device is, I'm sure many of you are thinking how tacky it looks - especially since this is something designed for use on the move, potentially in public, and more importantly, something that will be carried around a lot. It needs to be far more robust than some plastic and paperclips.
Which is why today whilst I was in town buying some clothes, I also popped into Maplins and picked up: a battery holder; another adapter tip; some wire; some insulation tape; a pack of Energizer Ultimate Lithium AAs; and with my newfound expertise in electronics, I quickly threw together this:
Works just as well, is nice to hold, is much more robust, and looks okay.
The cost of the components for this second one came to �8.58, including �4.99 for the Energizer Lithiums, and I still have nearly 10m of wire and at least 3.5m of tape left. Which should come in useful for future projects...
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