This follows on from a previous thread which was around at the end of
December into January.
The thread saw me musing about how to put lights into a unicycle rim to make
it look more interesting in the dark.
Since January I have assembled something.
Technical people might like to know this (less electronicsy folks would
probably prefer to skip a paragraph or two and get to the video 
:
The wheel contains 18 12V 90mA bulbs in panel mount (10mm diameter)
Miniature Edison Screw bulb holders. The wires, four of them - one for each
of the 3 sets of 6 bulbs and one common, run inside the rim. To stop the
soldered connections of the bulb holders touching the rim and shorting the
rim is lined with duct tape. The wires sit underneath the rubber rim strip
that was originally on the rim. Owing to the increased rim thickness the
tyre was reluctant to go onto the wheel but brute force and ignorance seated
it in the end.
The wires, housed in heatshrink tubing, come out of a grommetted hole in the
rim, opposite the valve, and terminate in a 4 pin weatherproof connector.
The control box contains one PIC16F628 4MHz microcontroller which runs from
a 5 Volt regulator, three ZVN4310A N-Channel Enhancement Mode MOSFETs - one
for each string of lights, a button, a DC input jack and a weatherproof
connector to connect to the wheel.
The PIC sends a Pulse Width Modulated drive signal to the gate each MOSFET
which drives the ground side of the corresponding string of bulbs. All bulb
strings have 12V (or whatever is applied to DC input of the control box) on
the other side. The PWM is software-driven with 5 bit resolution. This means
that each string of 6 bulbs can be set to one of 32 brightness levels rather
than just off or on - smooth fading is achieved this way.
The button tells the PIC to change to the next pattern and will eventually
be debounced in software since there’s no hardware debouncing on it.
I haven’t yet reattached the cranks or tried riding on what may turn out to
be a severely weakened wheel. Nor have I sorted out a power supply. It looks
like lead-acid batteries are the (expensive) way to go. When all the bulbs
are on at full brightness they run at 1.62 Amps. This is just over 20 Watts
which is quite bright, as unicycles go. Using a NiCd 10xAA battery pack
(600mAh) would only provide 20 minutes of on-time which would be ok for an
act in a show but not much good for a parade.
I only have a 9V 900mA supply so the bulbs don’t reach full brightness
(though that’d be difficult to see on a QuickCam anyway) but here’s a link
to the video of the wheel executing a fading rotational pattern:
http://feldhaus.co.uk/lights/wheel.avi
(171kB)
You’ll need the DivX Codec v4.12 - if you don’t have it already you can get
from here:
http://feldhaus.co.uk/lights/DivX412Codec.exe
(566kB)
I’ll try to get a video of the whole unicycle once it’s assembled. I still
have to sort out batteries and rewrite the software.
Sorry for the long post (it’s Saturday, I should be giraffe riding but my
left knee hurts dauntingly when I do so I thought I’d better give it a
rest.)
Andrew Feldhaus
Owner of possibly the world’s only unicycle with 20 Watts of lighting and a
4MHz CPU
0xADF
P.S. Harper, I believed your claim of
3-hours-until-you-nailed-a-6’-giraffe-freemount because it’s as more
believable than claims of riding on an FN tandem van-de-Graaff accelerator
and claims of designing and building an epicyclic geared hub