Build Your Own Bike Turn Signal

Keep safe and alert others of your electronics skills

By Kevin Taylor

The savvy cyclist already has the various blinkers and lights to make a bike a beacon at night, but navigating surface streets in the evening is still a gamble. Hand signals aren't very visible to cars, even with a reflective jacket. So here's the electronics fan's solution: a bike turn signal, using flashy luminescent wire. Light up the night and stay safe in style, even during turns and lane changes.

To give you an idea of the simplicity and affordability of the project, Jameco's package of starter grab bags provided all the electronic components, except the 555 timer IC.

This was the first flashlight I set out to improve. This being my first attempt, I tried for the simplest possible strategy.

Sewing the ArrowDrafting and sewing the arrow pins help keep track of the path
The Vest

A bike vest or jacket is a smart idea; it's useful as a windbreaker, a visibility aid and now also as a mounting area for your turn signal. The first thing I did was sketch out on a piece of paper the shape of the arrow I wanted (actual size). Go for a triangle or simple arrow shape since the luminescent wire doesn't like to stay bent in sharp turns (my complex arrow design was probably a mistake).

My vest had the advantage of being slightly see-through, so I spread it out flat, placed the paper underneath it, bent the wire into its approximate shape, and began to sew the luminescent wire into place with clear nylon thread. Be sure to start where the power cable meets the luminescent part. If you have extra left over at the end, it can be clipped off and resealed with a bit of tape or dab of hot glue.

After the arrows took their shape, I poked a hole in the vest for the wires to run through, and sewed them to run down the inside, since I didn't want them interfering with my arms during a ride.

I now possess a glowing vest! Blue light is a great color for this because it can't be confused with traffic lights or brake lights. After playing around with it for a while, I moved onto the electronics.

Finished VestFinished Vest

Electro Hijack The Hijacking Master Plan


So now we have to devise a way to activate the luminescent wire, but this turns out to be no simple task. After a little investigation, it turns out that the mini circuit board inside the luminescent wire's battery pack is doing an impressive amount of processing: It turns 3V DC into a high voltage, 3KHz square wave. So instead of reverse-engineering it, I decided to hijack it. (For electronics gurus and masochists, the input yielding greatest brightness is a 3.6KHz square wave, 110V peak-to-peak.)

Here's how the hijacking happened: I unscrewed the casing and removed the circuit board, yanking the power wires from the battery case, since I'd need longer wires anyway. The target here is the 4-pin integrated circuit – the small piece of circuit board standing up with a black blob on it – all we need are its connections. I wiggled it out of the board. Activating the output pin when the board was powered lit up the wire. Bingo.

The objective was to activate the output pin intermittently, so the blinker would flash like a regular car turn signal; half-on, half-off, about once per second. This is just the task for the 555 timer chip. For an excellent explanation of how to use 555 timers, visit this page.

The actual power to the light comes from the small transformer on the board, where the wires from the plug are connected. This signal is going to go through a three-way switch, to select left-signal, right-signal, or off, so I didn't need the original plug there. I reinstalled it elsewhere.

The original wiring is far too short to reach all the way from my vest to the handlebars, where I planned to mount it, so I decided to splice in a few extra feet of power cord. I found regular two-strand wire from some retired electronics, measured two lengths, and attached one end of each to the switch output, and the other end I soldered to the wire's female plug. Braided together, the power cords are hardly noticeable when I ride. I made sure that I wouldn't mix up the plugs by painting one pair of them white.

The red LED built into the board is a handy power indicator. I wired it all up on a project board, hijacked circuit board and all. See the circuit diagram below for details.

I used the original battery holder, after snapping off the excess plastic, but it wasn't very reliable without its cover. It made for a rather clunky package. A separate battery clip would have been ideal. I wrapped my creation up in electrical tape, which was certainly not the most elegant route to take – invest in small enclosures if you plan on making your own.

Saddling Up

The rather unsightly package was then zip-tied to a former odometer mount. Again, in my workshop, a quick solution usually wins out against a more robust one.

The wires easily clip in to the vest, without restricting my movement, and pop off easily when I'm finished. To store the excess wire when I'm not riding at night, I wrap it around the handlebars and tuck it in.

How well does it work? In direct sunlight, it won't show up very well. Once the sun goes down, however, the arrow shines boldly and nobody on the road can miss it. No more nerve-wracking nighttime rides.

There are plenty of ways to improve on my design – reducing the number of switches to just the three-way switch with a little help from a transistor or more prongs, packaging it up in a nicer way, to name a few – share your improvements at [email protected].

Parts List

Part Description Mfr. Part No.
Grab Bag Package GB197
555 Timer LMC555CN/NOPB
Light Wire NWRB15
Prototype Board G/S(PCB228)-R

Parts Recommended

Part Description Mfr. Part No.
Small Enclosure H2855-R
Battery Clip BH-321-4A-R
Power Cable GOLDSUN – WIRE 100'
Slide Switch MS-306-R
Toggle Switch 35-3005-BU
3KΩ Resistor CF1/4W302JRC
220µF Capacitor EC22016H611-R
1N4148 Diode IN4148
Finished CircuitThe finished circuit in a less-than-pretty package


Bike Handle


Note: Please check your local laws to make that you aren't violating any traffic regulations.

Kevin Taylor loves to repurpose old or broken things into a new creations through electronics.