The Idea is to take a basic cheap bike helmet and make it interesting and safer. I did this by adding 4 Superbright LED's and some reflective material. This Instructable is a very good one to attempt if you are just getting started in electronics and soldering. This is because it is not a very costly instructable (as far as electronics go) and the skills needed are very basic. It is also a great application of Ohms law!
Step 1: The Theory
Ohms Law states that I = V / R . In this, I is Current in amps (or mA as it is in LED's), V is Potential Difference in Volts, and R is Resistance in Ohms
Since this equation is used for the whole circuit, it isn't very useful to us the way it is now. We have to change it so it will give us the resister value we need. This Equation is:
R= ( Vs-Vl ) / I
Vs is the supply voltage; what come out of the battery. In this project it is 9 Volts.
VI is the LED voltage. It is the voltage the LED should have. It is stated on Data sheets you can find usually at the web site you bought your LED's from. In my case, the white LED's I have were 3.5 Volts.
I is the Amperage the LED operates at. It is usually 20 to 30 mA ( 0.02- 0.03 Amps). It can also be found on the data sheet for your LED. Mine was 20 mA.
So if I was to attach 1 White LED to the battery I would have
R= ( 9 - 3.5)/ 0.02
R= 275 Ohm
This means that you want to have at a minimum a 275 Ohm Resister, however to sustain battery life it would be smarter to use 300 to 330 Ohm Resister
Now, because one LED is kinda wimpy for a head light we will put the LEDs in not only in series but in series and parallel!
The math gets a little more complicated from here on.
If we put 2 of these white LEDs in series we have to use the equation
Vl = Number of LEDs x LED Voltage
Vl = 2x3.5
Vl = 7
R= (9-7)/0.2 *IMPORTANT* Number of LEDs does not change the Amperage in the equation*
R = 100
ok, so we can do 2 LED's in series, but can we do 3?
Vl = 3 x 3.5
R= ( 9 - 10.5 ) / 0.02
We cannot have a negative resistor so we have to keep with 2 in series, but we want to have 4 LED's. The way to do this is to have two sets of two LEDs series in parallel. Okay, that is really badly worded, but the picture below should clarify it a lot.
Now that you understand the process go and try it out with your LEDs.
If you are not good at all this math stuff you could just enter your info onto
However if you know how and why your circuits work it makes everything much easier when you get into more complicated electronics.
The Illustrations were created on Yenka and edited on Photoshop Elements
Step 2: Materials & Tools
-9V battery clip
-4 LEDs-- I used white but any other colour would work, too.
-2 resistors (Value will change based on LED's, more info in next step)
-a switch of some sort, not a momentary; a flip or slide would work well here
-a good amount of wire, solid core works best but stranded is fine
-foam for cushioning
-solder-less bread board
-hot glue gun
-needle nose pliers
-Dremel tool (not needed but makes it easier)
-pen knife (not shown)
Step 3: Bread-boarding
If you need to know how to bread-board or you would like to know more about how they work I would recommend to check out Cew27's Instructable on Breadboard Basics
Step 4: Soldering
Now you want to solder the resister to the negative lead on each LED set. It doesn't matter if you solder the resister on the positive or negative lead, but if you keep your resistors on the negative leads as a general rule, then it makes everything easier because you don't have to keep in checking the polarity of your LEDs. (Picture 2)
Next, add about 3"-4" of wire to the + and resister. This makes connecting everything together easier later on. (Picture 3)
Step 5: Attaching LEDs
Step 6: Add Battery and Switch
I hollowed this space out with the pen knife. The Dremel tool works, but it takes longer. You also need to keep the new hole space snug to the battery. This is because the battery is not held in with anything but the elasticity of foam, so don't go over board with the knife.
Then solder the + from the battery clip to one of the connections on the switch. Next solder a wire to a different connection. In other words, solder it so it works as a switch.
You will want extensions on the wires so they reach all the way to the front LED assemblies.
Step 7: Connect It All Together
To keep the helmet comfortable it is best to use the Dremel tool to carve a trench between the LED units and the middle space for the wires to rest.
Next, secure the wires to the helmet with electrical tape. This keeps the connections secure and makes the helmet more comfortable.
Step 8: Finishing
We are going to add foam to the inside of the helmet so you will not feel any of the new electronics we have added. Minimal addition of foam will make a difference. There is too much foam in the first few picture. I later cut it down to 1/2 to 1/4 of a inch. You can see it in the final picture
If you don't have foam it isn't really needed. Foam just makes the helmet a little more snug and comfortable.
I also added some reflective material to the back so I would be visible from the front and the back. It is sticky on one side. You could buy some similar products at
*I do not get a kickback, it is just a good site.
Step 9: Go Out and Be Seen
Other cool ideas that could be expanded on:
-Red LED's on the back
-Flashing LED's with a 555 timer
-Use your imagination!
Thanks for reading, and if you think this is a good instructable throw a vote my way in the Light Up the Night Contest.