If you commute regularly on your bicycle, the lack of sun in the winter can be a bit intimidating, particularly if your journey is not well lit. I ride my bike to work all year around, and in November, much of my commute is in the dark. I have a good set of lights (front and rear) to see where I'm going, but in the dark, people often don't notice hand signals. And of the folks that notice, many don't understand. I guess the left turn signal is pretty straight forward, but nobody really seems to get the right. And forget about stop and slow down... but I digress.

My goal is to create a very simple set of turn signals that anyone can build with a few basic tools. Where possible, I've used commercial, off-the-shelf parts, all of which should be available at your local bike shop, electronics shop, or online if you don't have access to these things in your town.

Disclaimer:
The recommended way to indicate turning is by using hand signals, and these shouldn't replace that. These are rear turn signals only. You still need to indicate you intention to turn to the people ahead of you.

Step 1: Required Parts

To build this, you will need the following (prices in Canadian Dollars):

Parts:
1- Two Rear flashing bike safety lights: $10.50 each
I used Blinky7 lights from Planet Bike. I got them from Mountain Equipment Co-op here in Canada. Probably REI in the US would have the same thing. Important: The lights must have a blinking mode, and the blinking must be sustained when the batteries are removed, and put back in. The lights I used have a capacitor that slowly discharges. This means that if I don't use my turn signals for 20 minutes, the light gets reset to a solid light and I have to press the switch on the light to set it back to blinking mode. Ideally, your light will have a switch that will remember the blinking setting indefinitely.

2- One AAA x2 battery holder : $1. Get one with a case to keep the batteries dry.

3- One Double Pole Double Throw (or DPDT On/Off/On for short) switch. $5.50
I picked up both of these items at Lee's Electronic - my goto shop for electronics in Vancouver. Probably Radio Shack would have something similar. My battery case has an on/off switch, but that's not really required, as the switch will be used to turn them off. If you can find a waterproof switch, that would be ideal.

4- Wire. Red and Black. 6 feet of each should do, or enough to go from your handlebars to the just at the top of the seat stays and back. 26 gage or so should be fine, but anything reasonable will work.

5- one extra long screw that will fit the nut of the Blinky mounting setup.

Tools:

6- a little silicon , similar to the stuff that you would use to seal around your bathtub. Caulking, Shoe Goo, or Goop will also work.

7- A little strip of adhesive Velcro (both sides)

8- Solder and a solder iron. Or you could use silver conductive epoxy if you don't have access to a soldering iron.

9- Xacto knife

A set of helping hands (the mechanical device, not another person), and a set of wire cutters were also used, but you could get by without them.

Step 2: Determine the Location for the Switch and Lights

In this step, we'll figure out where the switch bracket will go, and where the two light brackets will go. Then we'll measure the distance roughly, and cut the wires we need.

The first step should be to figure out where the switch will go on the bike, then temporary mount it.. This should be done first for a few reasons:

1) It will tell us the orientation of the switch. I changed my switch position, and now the toggle goes up and down instead of left and right

2) We need to know this to measure the wire

3) It will ensure that the switch won't interfere with the handlebars or turning of the bike.

Pic 1- So take one of the large mounting brackets and decide where you want the switch to go. Make sure it fits with the additional using the additional bolt. The bolts that come with the kit will be used to mount our lights. Also, be sure to try turning bars back and forth to make sure the wire is long enough. Use this measurement to cut two black and two red wires. Put them aside for now and remove all the brackets.

Pic 2- Now, figure out where the lights will mount to using the small brackets. From here, roughly measure the length of wire you will need. Make it a bit longer then you think. We'll trim it later.

Pic 3- Make sure that the lights do not interfere with the brakes!

Step 3: Build a Mount for the Switch

Now we will build the mount for the switch out of the piece of plastic. Again, I just used a piece of rather solid plastic I had laying around. You could use metal, but then you'd have to drill it rather then ream it with the xacto knife. We need three holes in this piece of plastic, one for the switch to go through, a smaller one for the prong on the switch so it doesn't spin when you flip it, and a third that will attach the plastic to the bracket to make it a single unit.

Pic 1: Ream a hole in the plastic big enough for the switch to fit through. Do this by taking the xacto knife and spinning it while putting a little pressure on it. Soon the knife will pop out the other side. Continue until the hole is big enough for the switch.

Pic 2: Notice that your switch comes with a little washer type thing with a prong sticking out of it. This is so the switch doesn't spin in the hole. Put the switch through the hole and mark where the prong is.

Pic 3: Then we'll ream another smaller hold for the prong to go through.

Pic 4: Assemble the switch in the mount and see if it's solid.

Pic 5: Next we have to see how the mount is going to fit with the bracket. At this point, I had to carve a bit off the plastic to get it to fit right. Once that's done, mark where the hold should go in the plastic.

Pic 6: Ream out the hole for the bracket and assemble it. Make sure if it's sturdy enough.

Step 4: Solder the Switch

DPDT on/off/on switches are very simple, despite the acronyms. When you look at the back of the switch there will be two 'channels' of pins, separated by a ridge of plastic. Each of these channels act independently. In this case, we will use one channel to connect all of the positive wires, and the other channel to connect the ground wire.

Pic 1 (from http://www.decdun.me.uk/gainclonepre.html): From our battery pack, we will connect C to the positive wire (red) on the battery terminal, and D to the ground wire (black). When we flip the switch to the right (if we were facing it), the C and E pins will make a connection, as will the D and F pins. If the switch is flipped the other way, the C and A pins will connect, as will the D and B pins. When the switch is in the middle, no full connections are made, so both lights will be off.

Pic 2: Solder the battery pack to C (+) and D (-). Then solder the remaining two red wires to E and A, and the two remaining black wires to F and B.

Step 5: Mount the Switch and Run the Wires.

Attach the switch in the desired location using the longer screw that did not come with the lights. Note that the battery pack is just sort of hanging there for now.

Step 6: Secure the Battery Pack

For this step, we will secure the battery pack to frame. In my case I'm going to use the handlebar stem.

Pics 1 and 2: Attach Velcro to the battery pack and the frame (or stem in my case). Be sure not to obstruct the on/off switch if your battery pack has one. This Velcro won't be enough to keep the battery pack on by itself, but it will keep it from sliding around on the frame.

Pic 3: Use one of the Velcro straps that came with one of the lights, and wrap it around the battery pack and the frame. It should be long enough to go around a couple of times. Between the stickon Velcro and the strap, the battery pack should be secure at this point. If it's still not solid, perhaps try some electrical tape.

Step 7: Attach the Lights

Pic 1- First ream a small hole in the back of each battery cover for the lights. It should be just small enough for the two wires to fit through (no pic for step - sorry!).

Pic 2- Then push the wire through and tin the ends of them if they are not tinned yet. Since the whole apparatus is attached to the bike via the switch, it can be a little awkward.

Pic 3- Solder the wires to the battery terminals. If you don't use too much solder, the lights can be reused later in their original way. If you look closely at the battery case, you'll see that one end has the positive and ground contacts actually connect, while the other does not. You must solder the wire to the battery posts that are not connected to each other (ie. the ones closest to the switch in my light). Test the lights at this point.

Pic 4- Once the solder has cooled, pull the wires through as much as you can, while still allowing access to the inside of the case. Apply the silicon to the hole where that the wires go through in order to keep the water out. I applied a bit to the inside and the outside.

Step 8: Secure the Wires

Pic 1- Take the remaining Velcro strap and cut it in half length ways to make two skinny straps. Use these straps to wrap to secure the wires to the frame, so there are no dangly bits.

Step 9: Future Enhancements

A few things I've been thinking about that would improve this:

1) add some sort of inline connection so the lights could be unclipped and removed.
2) use waterproof switch
3) figure out some very simple inline mechanism that will make any light flash.
4) Perhaps find a way that will incorporate an arrow in the direction to more clearly indicate that they are turn signals, and not just two blinking lights.
5) Maybe use orange lights?
6) Perhaps find a way to mount the lights further apart to make it more apparent that they are turn signals?