MY motorbike instructor asked if I could make a device which, when fitted to a motorbike, will give off an audible alarm when the bike reaches 50kp/h. The recent changes to the UK bike test weren’t entirely sensible – they include a manouvre that has to be done at a minimum of 31.07 mph (=50 kph), in line with the rest of Europe. Our bikes don’t all have kph marked on them, and certainly not clearly enough for a rider to see at a glance whether they’re going quick enough. So, the Bike Bleep – a box you fit to a bike, calibrate once (with a satnav or similar) and then it’ll let you know whether you’re going fast enough without you having to look away from the road ahead. My first proper foray into electronics since A-level Physics, many years ago…

Got the code working on a breadboard / prototyping board, using an Arduino Nano (well, a clone):

… and then transferred it to a veroboard.

Smaller, and waaaay more portable than the prototype, but pretty ugly, and too labour intensive:

So a custom PCB was needed. I dsigned the layout of the board and printed it out on laser transparency (OHP acetate), and taped it to a bit of UV-sensitive copper-clad board.

The problem was exposing it – to transfer the pattern to the copper takes UV light, and the cheapest UV light box I could find was about £130 from Maplins. Luckily, it seems UV LEDs work just as well (if a little untraditional) so I made up a board with lots of them:

.. and exposed the board for 5 minutes:

You could just about see the pattern on the copper, but to properly develop the board it needed dropping in a caustic soda solution:

The caustic soda removed the etch-resist wherever the UV had hit it, leaving a perfect pattern of tracks on the copper.

Next, the board is dropped in acid, to etch away all the unwanted copper:

Once rinsed off, you end up with a board with your design of copper tracks left on it.

Next: drilling holes for all the components. Takes a really small drill bit. Really really small.

All the holes done! Most of them in the right places, too.

Next, time to fit the components. Poke their legs through the right holes, and solder into place.

Finally, all the components in place:

The bottom of this board is a lot tidier than the veroboard one at the beginning.

The board is put in a little box with a battery, and connected up to the power switch, a piezo sounder, and a magnet sensor (Hall Effect Device) that will be fitted by one of the bike wheels.

The box fits under the motorbike seat:

with a little power switch for the rider to turn it on and off:

A magnet is fixed to the rim of the wheel, and the sensor fitted nearby:

When the box is switched on with the little switch on the handlebars, it does nothing until you hit the magic speed, then it outputs a really loud beeeep to let the rider know they’re going fast enough. Simple enough.

Well – that’s it for now – the bike school is going to test it out for a few days and see whether it helps the riders (or distracts them…)