Okay, so inspired by Iceniner's example and the fact that my Mum bought me a lovely adjustable soldering iron for Chirstmas that I still hadn't tried out, I decided to finall get around to moving on a bit further with my rangefinding device.
Well, I've managed to just about build my very first circuitboard, so I'm quite pleased with myself, despite the fact I almost completely screwed it up several times. It's wired exactly the same as my previous prototype, except that everything is now soldered on to some stripboard rather than just plugged in to some breadboard, so it shouldn't just fall apart when I attach it to the bike. It all plugs in to my Arduino prototyping board, and it all works as before.
All I need to do now is a little more work on the software, as it currently just gives you a running readout of how far away things are, whereas ideally I'd like it to tell you what the closest thing was within the last five seconds, or something like that. I also need to work out how to fix it to the bike, which might be a pain as the board is slightly too big to fit into any of my current project boxes.
Anyway, once that's done all I need a dry day to try it on as the ultrasonic unit isn't water resistant.