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Step 5Circuit Construction...
This page covers the construction of the electrical circuit outside of the bicycle.
I built the unit to be triggered by the right hand grip because I use my left hand to signal when I ride in traffic. For this reason my instructions are written as left side and right side indicating the sides of the handlebars as they appear when you are sitting on the bicycle's saddle.
1) Cut a piece of speaker wire long enough to extend all the way through the handlebars. This will be the power lead for the right LED.
2) Solder the right LED onto one end of wire you just cut making sure to pay close attention to which is the positive and negative lead.
3) Cut another piece of wire about 8 inches long and solder the left LED onto one end. Again, pay attention to the polarity of the leads.
4) Stack your batteries so they are in series.
5) Take a 6 inch piece of wire with the ends stripped about a quarter inch and put 1 wire against the top and bottom of your battery stack. Make sure the negative wire is not touching the side of the battery as the sides are positive and will cause a short.
6) Carefully wrap the batteries and wires with electrical tape. You need to pull the tape snug to ensure good wire contact. I recommend wrapping tape around the ends of the batteries to hold the wires down first, then a second piece of tape around the circumference of the batteries to hold them in alignment. This is a quick and dirty method of securing the batteries. If you know a better method of securing the batteries inside the handlebars please let me know in the comments section and I will update this step.
7) Solder the resistor to the end of the negative battery wire. Unlike the LED's, the resistor can be attached either way so just pick an end and solder it up.
Now you should have 4 electrical parts of the project sitting on your workbench. These parts are the left LED assembly, right LED assembly, battery assembly, and a lone reed switch.
8) Take both LED assemblies and locate the positive wires. Solder both positive wires to one end of the reed switch. Keep in mind that for ease of assembly the left LED wire will need to run back along the length of the reed switch. This wire can be soldered backwards.
9) Next you can solder both negative wires from the LED's to the open end of the resistor you soldered to the negative battery wire in step 7.
10) Solder the positive battery wire to the open end of the reed switch.
11) Now you should be able to test your circuit. Take your magnet and pass it near the reed switch. If the lights come on, skip to step 13. If the lights do not come on or will not stay on proceed to step 12.
12) If your lights failed to illuminate in step 11 you need to do a little troubleshooting. It is best to start at one end of the circuit and work backwards until you find the problem. The first place I would check is the battery connections. If they are okay, check the polarity of the LED's to make sure they are not backwards. Finally, you can check the connectivity of your solder joints and the function of the reed switch with an electronic multi-meter. Fortunately this circuit uses a minimal number of parts so troubleshooting is not too bad.
13) Congratulations! If the test worked, you have completed the hardest part of the project and you are just moments away from bike-light completion. The final steps in the assembly process do not require soldering so go ahead and unplug your soldering iron if you have not already.
14) Tape the reed switch to a piece of car washing sponge that is shaped like a cylendar. Size will vary because of differences in handlebars but it should be roughly 1 inch in diameter and about 2 inches long. This sponge will hold the delicate glass switch in place inside the handlebars. You may want to test fit the sponge prior to attaching the reed switch to ensure it is the correct size. If you cut the sponge too big it will be difficult to insert, and if you cut it too small it will not stay in place. One car washing sponge can be cut to make many of these cylendars. You can try several different sizes and shapes until you find one that works well for your application.
15) Pull the plugs out of the ends of your bicycle's handlebars. They should just pop straight out but I have been known to use a bit of persuasion from a small screwdriver if they are not cooperative.
16) Select a drill bit that is the same diameter as the LED's you chose. Carefully drill a hole with your selected bit in the center of each of the plugs you took from the bike. You can test fit the LED's that you have just wired up but do not fully install them into the plugs yet.
The next step will cover the actual installation of the light assembly on the bike.
I built the unit to be triggered by the right hand grip because I use my left hand to signal when I ride in traffic. For this reason my instructions are written as left side and right side indicating the sides of the handlebars as they appear when you are sitting on the bicycle's saddle.
1) Cut a piece of speaker wire long enough to extend all the way through the handlebars. This will be the power lead for the right LED.
2) Solder the right LED onto one end of wire you just cut making sure to pay close attention to which is the positive and negative lead.
3) Cut another piece of wire about 8 inches long and solder the left LED onto one end. Again, pay attention to the polarity of the leads.
4) Stack your batteries so they are in series.
5) Take a 6 inch piece of wire with the ends stripped about a quarter inch and put 1 wire against the top and bottom of your battery stack. Make sure the negative wire is not touching the side of the battery as the sides are positive and will cause a short.
6) Carefully wrap the batteries and wires with electrical tape. You need to pull the tape snug to ensure good wire contact. I recommend wrapping tape around the ends of the batteries to hold the wires down first, then a second piece of tape around the circumference of the batteries to hold them in alignment. This is a quick and dirty method of securing the batteries. If you know a better method of securing the batteries inside the handlebars please let me know in the comments section and I will update this step.
7) Solder the resistor to the end of the negative battery wire. Unlike the LED's, the resistor can be attached either way so just pick an end and solder it up.
Now you should have 4 electrical parts of the project sitting on your workbench. These parts are the left LED assembly, right LED assembly, battery assembly, and a lone reed switch.
8) Take both LED assemblies and locate the positive wires. Solder both positive wires to one end of the reed switch. Keep in mind that for ease of assembly the left LED wire will need to run back along the length of the reed switch. This wire can be soldered backwards.
9) Next you can solder both negative wires from the LED's to the open end of the resistor you soldered to the negative battery wire in step 7.
10) Solder the positive battery wire to the open end of the reed switch.
11) Now you should be able to test your circuit. Take your magnet and pass it near the reed switch. If the lights come on, skip to step 13. If the lights do not come on or will not stay on proceed to step 12.
12) If your lights failed to illuminate in step 11 you need to do a little troubleshooting. It is best to start at one end of the circuit and work backwards until you find the problem. The first place I would check is the battery connections. If they are okay, check the polarity of the LED's to make sure they are not backwards. Finally, you can check the connectivity of your solder joints and the function of the reed switch with an electronic multi-meter. Fortunately this circuit uses a minimal number of parts so troubleshooting is not too bad.
13) Congratulations! If the test worked, you have completed the hardest part of the project and you are just moments away from bike-light completion. The final steps in the assembly process do not require soldering so go ahead and unplug your soldering iron if you have not already.
14) Tape the reed switch to a piece of car washing sponge that is shaped like a cylendar. Size will vary because of differences in handlebars but it should be roughly 1 inch in diameter and about 2 inches long. This sponge will hold the delicate glass switch in place inside the handlebars. You may want to test fit the sponge prior to attaching the reed switch to ensure it is the correct size. If you cut the sponge too big it will be difficult to insert, and if you cut it too small it will not stay in place. One car washing sponge can be cut to make many of these cylendars. You can try several different sizes and shapes until you find one that works well for your application.
15) Pull the plugs out of the ends of your bicycle's handlebars. They should just pop straight out but I have been known to use a bit of persuasion from a small screwdriver if they are not cooperative.
16) Select a drill bit that is the same diameter as the LED's you chose. Carefully drill a hole with your selected bit in the center of each of the plugs you took from the bike. You can test fit the LED's that you have just wired up but do not fully install them into the plugs yet.
The next step will cover the actual installation of the light assembly on the bike.
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