Tuesday, September 05, 2006

A modern Difference Engine?

The Difference Engine was a mechanically-powered device which could perform a limited (but useful) set of calculations. As Wikipedia says: "This machine used the decimal number system and was powered by cranking a handle."

I've blogged briefly about my Zaurus before. It remains very useful, mostly for Japanese learning, email/web access and occasionally writing (typically blogs, more rarely scientific papers). However, it has a limited battery life of at most 8h, and much less when using the web. So I've investigated a number of options for recharging it when I go on longer trips away from civilisation - especially long mountain trips. (Yes, I know what you are thinking - why does he need to take that up the mountains? But the email doesn't work up there, it is only used for Japanese language and other amusements in the long afternoons spent idly at the huts.) Previously, I've often carried 4 AA NiMH cells which are an adequate substitute for the proper charger, together with a solar charger to top these up (the solar power is too much of a low trickle to directly power the unit reliably). But although this works, it's a bit of a hassle to set up and also annoyingly heavy given its relative "luxury" status for a walking holiday.

Recently I found a small hand-cranked dynamo, sold as an emergency mobile phone charger. It was only 5 quid, although the postage to Japan was as much again. And voila - the modern Difference engine - turn the handle to power the machine!

It claims an output of up to (limited to) 6V, and when applied to the load of the Zaurus (which has a 3.7V 1800mAh battery) it drops to around 4V or so. I haven't accurately checked the current, but I'd be surprised if I could get it above 500mA - perhaps 200mA is more realistic. It weighs about 70g, which is less than 3 AA cells, let alone the solar charger. I haven't actually used it in anger on a long trip yet, but it seems to work just fine in short tests. I guess it should also hook up with no problems to all sorts of USB-powered (=5V) gadgets with an appropriately-wired plug, so long as their current draw isn't too high. But follow my example at your own risk...


Anonymous said...

I don't know about their respective outputs but you can get gedgets like this that also have a torch that can be powered by the handle, thus potentially saving more weight.


James Annan said...

Well this one has a single LED - but it wouldn't win me any friends if I used it in the middle of the night in a mountain hut :-)

I actually have one of the early hand-powered radios back in the UK and now there's quite a variety of radio/torch/chargers available, but the attraction (to me) of this dynamo is that it's really small and light.

Anonymous said...

Just store the energy from when you walk down the mountains. Shoot, store it and use it to walk back up the mountains.