Homemade Bicycle Turn Signals


  1. Introduction
  2. Purpose
  3. Design
  4. Materials
  5. Electronics
  6. Construction
  7. Mounting
  8. Results
  9. Photos


This page documents the design and construction of turn signals and brake lights for a bicycle. Because the idea of creating this page was formed after the turn signals were constructed, there unfortunately are not any pictures of the device during construction. There are numerous photos of the device and its components after completion, however. Because each photo has a dozen places in the document where it is logical to include it, I have instead placed all the photos in their own section at the bottom of the page. Clicking on each photo will bring up a much larger version in a new window.


Anyone who has ridden their bike in traffic knows that it can be a dangerous undertaking. Navigating the same roads as vehicles which are an order of magnitude (sometimes two orders) more massive than you can be daunting. To compound matters, the addition of electronic turn signals to cars in the late 1930's have left the majority of the public completely clueless in regards to understanding hand turn signals, on which most bicyclists depend. Even when motorists are able to understand the hand signals given by a bicyclist, often the signals are not able to be given. Sometimes both arms are required to keep control of a bike or to stop, such as on curves and hills. Sometimes, it's just too taxing on the arms to hold a hand signal while the rider in waiting for a long stop light to change. And at night, hand signals might be completely invisible to motorists or other cyclists, leading to potentially very dangerous situations. For these and countless other reasons, hand signals are inadequate for many bicyclists.

The goal, then, is to create electronic turn signals for the bicycle. To be of value, they need to meet the following criteria: they need to be visible to motorists on the road, and easily understandable to everyone; they need to be easy to operate, allowing both hands to remain on the handlebars while doing so; they need to not interfere with other functions of the bike, including pedaling, shifting, braking, cargo carrying, turning, etc.; and they need to have a power source that will last for the duration of a long ride (at least a single fifty mile ride, but preferable if the power source would last longer, or indefinitely). As you will see, the result meets all these criteria, as well as providing even further functionality.


After putting significant thought into the desired goals of the project, optional features desired, and the feasibility of implementing them, the following design was decided upon. The primary body of the device would consist of three parts; a right turn signal, a left turn signal, and a brake light. These parts would be connected together to form a single bar. Contained inside this bar would be all necessary circuitry and power sources. A single cable (cat 5 was chosen for this purpose due to it's common availability and the large number of individual conductors it has (8)) would run from the light bar to the handlebars, where it would connect with the switches. The switches would be mounted on an old front reflector, chosen because it attaches well to the handlebars without any modification. The turn signal switch would be placed so as to be activated by the thumb, and the brake switch would be connected to the brake lever.

Additionally, a problem regarding MP3 players would be addressed. When wearing bike shorts, one may be without a pocket in which to place an MP3 player. I, however, always carry at least one pannier with me (which holds things like a pump, spare tubes, emergency lights, food, etc). By integrating a 3.5mm headphone port into both the light bar (which will be placed at the rear of the bike near the pannier) and a second port near the controls on the handlebars, an MP3 player is able to be stored in the pannier without having to run the headphone wire around the rider.


Electronic components

  • 20 red LEDs
  • 24 yellow LEDs
  • 4 transistors
  • 4 capacitors
  • Numerous resistors
  • 1 small circuit board
  • 1 rechargeable 9V battery
  • 2 meters category 5 cable
  • Lots of solid core wire
  • 3 3.5mm jack ports
  • 1 3.5mm jack plug
  • 2 9V battery clips


  • 2 RJ-45 connectors
  • 1 female-female RJ-45 coupler
  • 1 dead man's switch with long lever
  • 1 on-off-on switch
  • 3 plastic project boxes (found at Radio Shack)
  • 2 short bolts with matching nuts and washers
  • 1 plastic front reflector (handlebar mounted)
  • 1 small 'L' shelf bracket
  • Numerous zip ties


  • Soldering iron and solder
  • Hot glue gun and glue
  • Hand drill with drill bits
  • Wire tools (cutters, strippers, pliers, etc.)
  • Cat 5 wire crimping tool


A single battery will power both turn signals and the brake lights, each of the three systems being connected in parallel. There are two identical oscillation circuits, one for each turn signal. The reason for this (as opposed to having a single oscillation circuit off of which each set of turn signal LEDs branch) is because the setup with a single oscillation circuit will still draw a small current even if the LEDs are off. Confining one oscillation circuit to each LED set allows the switch to completely isolate the system from the battery, preventing drain when the lights are not in use. The LEDs are arranged in sets of 4 LEDs in series ended with a current limiting resistor (the 9V battery will power up to four 2.1V LEDs in series) and these sets are wired in parallel. The LEDs are then wired to the oscillation circuit. With testing on a breadboard, resistor and capacitor sizes in the oscillation circuit were chosen so that the LEDs flash at the desired rate (potentiometers could also be used in place of the resistors connected to the negative terminal of the capacitors to allow variable speed control). The final circuit diagram can be seen below (click to embiggen).

The two oscillation circuits in the diagram above were soldered onto a small printed circuit board (see the photos), and room was left to allow for the connections to the rest of the system that would be needed (four connections to the battery's ground, two to the negative side of each of the turn signal blocks, and two to the 9V source after the switch).


First, holes were drilled in the sides of the plastic boxes. Two sets of the holes for the bolts, and a second two sets of holes to allow wires to travel from one box to the next. A grid shape was traced one on the middle box (the one which would hold the brake light) and an arrow was drawn on each of the other two boxes (care taken to make sure they point the right direction in respect to the holes that were drilled). Using a drill bit the size of the plastic cap on each LED (if too big a hole is drilled, the LED will fall through the hole instead of just poking through), holes for each of the 44 LEDS were drilled. LEDs were then placed in each hole (red in the middle box, yellow on the side boxes) with special care taken in how they were rotated, so as to facilitate connecting them in the sets of 4 without the leads having to cross over one another anymore than necessary. Once placed, each of the LEDS were sealed in with glue from a hot glue gun, serving as much purpose to keep them from coming out as to waterproof the holes. The leads of the LEDs were twisted together as appropriate using needle nose pliers, the connections were soldered, and the excess length of the leads were removed with diagonal cutters. Resistors were then soldered onto the ends of the LED sets, and the sets were then connected together. Throughout, hot glue was added as an easy way to provide electrical insulation between the exposed leads (this method was used to save the effort of having to try to fit the LEDs on a circuit board while maintaining their proper positioning, as well as to save a little bit of space).

The boxes were then bolted together, with more hot glue being applied at the seams to provide more waterproofing and to retard rotation of the boxes around their one bolt connection. Three more holes where drilled into the boxes, one for the cat 5 cable and one for each of the 3.5mm ports (one would be used for the MP3 player, the other as a charging port). The ports were installed, the LEDs were soldered to the circuit board (using some extra wire), the battery was soldered to the charging port, and wires were run from that to the circuit board. Cat 5 was inserted its hole, the hole was sealed with hot glue, and its eight wires were connected to the the appropriate places: three wires for the MP3 player port (left, right, and ground); two wires to the 9V source (one for the turn signals, one for the brake [this could have been done with one wire had I wanted to, but would have required additional wire near the switches]); and one wire to each of the three LED groups (where the 9V source would return after having passed through the switches). Everything was placed inside the boxes and the lids to the boxes were screwed into place.

The controls were mounted on an old front reflector. A drill was used to weaken the plastic reflecting part until it crumbled away leaving only the black plastic base. A hole was drilled for the turn signal switch and a second hole for the 3.5mm port. The brake light switch was attached with hot glue. The wires inside the cat 5 were attached to the switches with care paid to match how the wires were connected to the light box. The cat 5 was then cut near the light box, and RJ-45 connectors were placed on the ends of the wires at the cut. This allows the light box to be removed from the bike without having to remove the controls or the cable running down the length of the frame.


The controls were simply mounted to the handlebars using the mounting device of the reflector base. The lever for the brake switch was zip tied to the brake lever. The original plan was to attach the light box to an old rear reflector, and attach that to the bike's seat post. This proved to interfere with pedaling though, and so a new mounting solution that moved the light box more to the bike's rear was devised. A small shelf bracket was attached to the rear rack mounting arms via a number of zip ties. The light box was then attached to this bracket (the boxes came with both a plastic and metal lid, and the bracket is sandwiched between these two). The RJ-45 coupler was attached to this bracket, and the cat 5 plugged into either end. Zip ties along the frame of the bike to run the cat 5 from the rear to the controls on the handlebars complete the installation.


Many times during the construction I questioned if my labors would yield fruitful results. Having completed the project, I can say that they most certainly have. The most noticeable improvement has been my ability to change lanes easily. It is common to need to move from the right-hand side of the road to the left in preparation for a left turn, and the turn signal has caused cars to slow and allow my lane change on numerous occasions, where before the hand signal indicating my desire yielded no results at all. The system is low maintenance (it only needs to be recharged every few weeks), reliable, and just plain works. I highly recommend this or a similar system to any bicycle commuter, especially those who commute during non-daylight hours.


Rear view of the light box with the box lids removed and the battery and circuit board pulled out.

A close up of the circuit board.

Rear view of the light box with the box lids removed, and the battery and circuit board placed in their normal locations.

The front of the light box.

The controls as seen from the rider's point of view.

The controls, as seen from the front of the bike.

The rear of the bike with the lights installed. This is what a motorist behind the bike would see.

A side view of the bike showing how the lights are mounted.