mouldy.org

This is a simple bike light which can be contructed with a minimum of tools. It is bright enough to be useful as a headlight, is fairly robust, and cheap to construct. It's perfect for commuting and does a surprisingly good job for mountain biking too.

The whole thing, including rechargeable batteries, weighs about 200g and will run for over two hours.

So after my recent set of mountain bike lights, I decided that I was ready to build what would be my be-all, end-all set of bike lights. These would be it. The Ultimate.

After the mountain bike lights, I wanted lighter, brighter, and longer battery life. I wanted to be able to use them for long road rides - so they can't use a bottle cage. I wanted to be able to commute without having to charge the battery every night. I wanted even more power for mountain bike riding and scaring pedestrians. I wanted lighter weight, so I could use them for fast group rides.

In preparation for the 2006 Sydney 24 Hour, I wanted new mountain bike lights. Last year's light was a 20W halogen globe and two packs of ten AA cells. This was nice and bright, but the battery packs got rather hot and only lasted about 40 minutes each.

This year, I raced solo. Recharging two battery packs per lap wouldn't cut it. My plan was to spend about an hour per lap - each lap was 10km - and sleep for an hour or two when I charged the batteries. So I was aiming for 3-4 hours battery life at about the same brightness as a the 20W halogen.

The new system weighs 715 grams and lasts for about four hours at 9 watts of output. Charging the batteries takes under two hours.

During development of my Sumo robot, I ran into some problems around controlling the H-bridges:

• If you're going to use PWM, the PWM signals on each input of the H-bridge need to be synchronised (phase-coherent), and there's no such guarantee when using an AVR to drive them. If they're not phase-coherent, the H-bridge will get hot and not drive the motor properly.
• I wanted to use braking on the H-bridge, which means I need independent control of all four H-bridge inputs. The ATMega32 that I was using has four PWM channels - more than most microcontrollers - but still only enough to run a single H-bridge.
  
  

Here's yet another way to build a battery-powered USB port. You can use it to charge your iPod or phone or lights or whatever. It should last about ten times as long as designs based on 9V batteries.

It's based around my favourite batteries of all time, AA NiMH cells. They're cheap, rechargeable, and perfectly suited to this project. I used this cable to keep my iPod charged on a bicycle tour of Victoria last year.