Speed Vest

By Mykle Hansen
Category: Electronics, Fun & Games
Time Required: 1-2 weekends
Difficulty: Moderate

This lightweight night-cycling vest displays your current speed in glowing, 7-inch-tall numbers easily visible to cars. On the back, an Arduino microcontroller reads input from an off-the-shelf bike speedometer sensor, and then switches power to sewn-in numerals made from electroluminescent (EL) wire.

Bicyclists receive a lot of honk-based grief from car drivers who perceive them as slow and in the way, and when drivers misjudge a bicycle’s speed, it can cause “right hook” collisions that kill several bicyclists each year. If car users knew how fast cyclists were moving, would they be more willing to share the road? What if a bicycle prominently displayed its speed to the cars behind it, using large, brightly lit digits?

Brady Clark, cycling advocate and design genius, asked me to help him answer this question. At first I assumed it was beyond me, since I was a software guy who barely understood electronics. But I love to learn, and the Dorkbot community in Portland, Ore., was encouraging and helpful.

Our final motivation was the Bike Gadget Contest in Minneapolis, sponsored by the Bell Museum and The Hub, a bike co-op. After some research and shopping, we completed this project in a manic three-day push, then delivered it to the contest judges within minutes of the entry deadline.

Steps

Step #1: Assemble the protoshield.

The ProtoShield lets you build circuits directly on top of the Arduino board. I assembled it following Atomicsalad’s excellent ProtoShield tutorial.
If you’re really in a hurry, you can leave out all the female headers. But if you might use your ProtoShield for other projects later, it’s better to assemble the whole thing (and you’ll still have to do a lot of desoldering.)

Conclusion

The Display Mannequin

With less than 12 hours remaining before our all-motivating contest deadline, we began work on our floor display. We made a mannequin to wear the Speed Vest by casting Brady, using Mark Jenkins’ packing tape sculpture technique (http://tapesculpture.org). Add one bicycle and one bicycle work-stand, and we were ready to wow the public.

SpeedVest II

It’s hard to know just how car drivers feel about the Speed Vest, but so far nobody bicycling while wearing it has been honked at or run over. Meanwhile, we’re now working on SpeedVest II, with four major areas of improvement:

Wirelessness If the rider forgets he’s plugged into the bicycle when he dismounts, the electronics get yanked. In practice, this happens almost every time, and we’ve had to resolder the connectors three times already. SpeedVest II will use Zigbee wireless modules to transmit speed data from the wheel to the Arduino.
Size In bicycle equipment, lightness is everything. The Arduino USB board is handy, but contains a lot of parts we don’t use. With a custom PCB design, we can get the whole system much smaller and lighter.
Power The Arduino is powered by a 9V battery, but the EL wire inverter has its own AA battery and a separate power switch. The batteries run out at different times, and turning the unit on and off is a two-step process. Our improved single-board design will integrate the inverter, driven from the same power source as the rest of the board.
Speed range Bicycles are fast, and getting faster! Our vest displays speeds up to 69mph, but the current bicycle land speed record is 81mph. (And that’s not even close to the drafting speed record of 152mph, set by a bicyclist chasing a specially designed car that pushed away the forward wind resistance.) So we’re redesigning our numeric display to show all speeds from 1 to 99 miles per hour. We hope that will suffice for normal use.

The Contest

We handily accomplished our first mission: winning The Hub’s Bike Gadget Contest. W00t!

Then we set about testing the Speed Vest in real traffic. We’ve had great success with it, and the feedback from everyone who’s seen it has been wonderful. Many people want their own.

Also, simulating a wheel with your hands, and seeing how fast you can make the speed display go, has become a strangely compelling party game.