Anti-speeding device?

I am going to be buying a new motorcycle soon after spending several hundred dollars clearing up my previous youthful errors with my last one. Anyways, I am thinking about rigging a bright LED to the top of the windshield that comes on when I go above a certain speed. Right now all I can think of doing is like in the old movies when then make a time-bomb is drill a hole in the face of a clock (speedometer in this case) and have a wire come in contact with the speedometer when it reaches a certain speed. If anyone can come up with a more efficient and elligant idea and how to do it please email me at Thank you ahead of time, Chris

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photozz10 years ago
Attach a small magnet to the wheel. Place a sensor near it, then program a PIC or such to read the pulses. when you hit a certain frequency, have it light a LED. Should draw very little current, and be reasonably easy to program. You could even have a series of LEDs to denote different speeds.
andy photozz10 years ago
Great idea, just like those speedometers you can get for pushbikes. For the non-PIC savvy you could use it to intermittently charge a capacitor (briefly increasing the charge in it every time the wheel rotates). Then you'd have the capacitor bridged by a variable resistor, the voltage in the capacitor would go up with speed. The higher the resistor value the faster the rotation needed to reach a given voltage. Then it`s a simple case of using a semiconductor relay or voltage detector with an LED. To set it just drive at the legal limit and adjust the variable resistor so that it just starts to light up. It would flash very(probably imperceptibly) quickly, so the further over the limit the brighter it would seem (up to a point) by the voltage bouncing up and down inside the capacitor. This is because of the after-image effect used in persistence of vision gadgets.
photozz andy10 years ago
not bad. I could see that requiring a lot of tweaking though. You could also use an IR detector through the spokes or something. lots of triggers here..
andy photozz10 years ago
One concern; The reed switch might not be able to switch on and off fast enough, you could use the semiconducter alternitive (i think they are called "Hall field effect sensors" (please someone correct me if im wrong)) but i have no idea how appropriate it would be, I have never used one before.
photozz andy10 years ago
I was thinking Hall sensor as well actually. the switch speed on a reed would not be fast enough about 5-10mph I would guess.
phreakiphred10 years ago
Uh, look at the speedometer.....?
frank2608011510 years ago
i have a more elegant idea, does not require you to damage ur bike at all put a motor against the wheel, it will act as a generator, now wire that to a adjustment potentiometer, then a zener diode set at a specific voltage when you go too fast, more power is generated, and the zener diode lets the voltage through, if there isnt enough power, the zener diode doesnt let power through. see attached circuit diagram, you need to experiment with the potentiometer and the zener diode not the best way, but should work, shouldn't it? if you can, use a photogate with a microcontroller funny story, i tried to make a thermostat that way before, didn't work well at all.
On a bicycle, perhaps. A small motor wouldn't hold up to the vibrations and speed of a motorcycle.