9 - Volt Headlamp

 This instructable will show you how to construct a simple and easy to use headlamp. I have decided to run the headlamp on 9 volts, which provides a bright white light used in this project. This project is a good starter project for those who are beginning to solder, and yields a useful reward when finished.

The headlamp will produce white light, however, it is also possible to replace the white LED's with other colors if you so desire. The LED's will be wired in parallel, so that each LED produces the maximum amount of light possible.

Tips:
*Tape up your exposed connections in this project with electrical tape. 
*Use a dry-erase marker to mark positions, because it rubs off if you need to adjust the position.
*Handle soldering irons and hot glue guns with caution - They are hot!
*Build the circuit on a breadboard to make sure it works and that your components work too.

Step 1 Components and Pieces

 Depending on where you go to buy the components, you can build this project for under $10.
You will need:
2 - high intensity white LED's (3.2 volts is common)
1 - customizable printed circuit board
2 - 470 ohm resistors (yellow, purple, brown in resistor color code)
1 - slide or toggle switch
1 - 9 volt battery plug
1 - 9 volt battery
1 -  small project box (can be a mint tin, I use a $0.59 battery box from Fry's electronics).
1 - headband 
3 - (separate pieces) 6+ inches of electrical wire (can be any gauge) or a spool of wire if you have         one.

To build the light, you will use:
A soldering Iron
Electrical Tape
Solder
Hot Glue

*I recommend buying your tools and components at Fry's or Radio Shack. Use a combination of components from both stores to take full advantage of pricing differences.

Comments

[wobbler]

You are wasting a lot of the battery's power in this circuit for no real gain. Two thirds of the energy is being dissipated (wasted) in the resistors dropping the voltage to 3.2 volts. You would be much better placing the diodes in series and using a single 220ohm dropper resistor. Both diodes will receive the same current and should balance out just fine in terms of voltage drop if they are the same LEDs. You are still wasting over a third of the battery power in the resistor like this, but this should now actually be taking half the current of your design and hence last twice as long. Admittedly, it will get less of the last drops of energy from the battery, stopping working at about 6v instead of 3v, but that will be more than compensated for by the lower current and also the fact that by the time the cells reach 6v, they are almost practically drained anyway. Plus, your component count is less. You also don't really need to connect the off connection on S1 to ground/battery negative. It's not doing any harm, but it's not really doing any good either in reality. You could also look for three diodes in series if you get LEDs with a lower combined voltage drop of 9v and use a lower value resistor to get more light/less wastage in the resistor, but the closer to the battery the voltage, the less the current regulating effect of the resistor so it's a trade-off. Keep on having fun with LEDs though, making lights is very addictive!

[pro5200]

Thanks Ericscrum for your sharing :)
Wobbler, I want to ask
it seems you are proficient in LED lights, may I ask your advice?
I have made a series of LED lights on my bicycle spokes, for driving at night I use a 9 volt battery with 9 pieces of white LED 3.3 volts, which I connect each with a 330 ohm resistor 9 pieces 1/4 watt. its durability is approximately 30 hours later the lights dimmed, is there any way to be more durable?

[wobbler]

You could firstly do what I've advised in my other reply and pair up the diodes in series with only one dropper resistor. This means less energy wastage as you are getting two LEDs worth of light per chain. However, the other issue is using 9v batteries, which are are relatively low in ampere-hours at 500mAh roughly. You could use a rechargeable 9v batteriy to keep your costs down but these have even less mAh of approx. 300mAh. Your other altenative is to use two AA rechargeable batteries in series with lower voltage LEDs (as close to 2v as possible) and then use smaller value resistors (maybe 10 - 47ohms for starters?). You could balance the weight of the batteries out by putting one each side of the axle. You can get rechargeabe AAs up to 2700mAh roughly so they should last considerable longer than the 9v battery and if using non-rechargeales, they should be cheaper.

You could also use other than white LEDs to get the LED voltage down, maybe green or amber?

As a final thought, don't use 9 LEDs. See if it looks just as good with 3 or 6. That also will increase your light life.

As an aside, I've often thought of doing this with either a slip ring contact to allow the batteries to be off the wheel or some sort coil passing a bank of super magnets, the reverso of some of the rear light ones you can buy but not got round to it yet (ever?) See Nagutrons http://www.instructables.com/id/Magnetic-Induction-Bike-Lights/ for the basic idea.

http://en.wikipedia.org/wiki/Light-emitting_diode
http://en.wikipedia.org/wiki/Nine-volt_battery

[pro5200]

ok thank you very much for suggesting a very useful.
If I use 2AA alkaline battery, the durability will be quite long, it's cheaper and I do not need to use another resistor is not it?

[wobbler]

Whether you need to use a resistor or not depends on the batteries' voltages, their internal resistance and the LED's voltage and driving current. LEDs always need a resistor to limit the current, but the resistance in simple torches is the internal resistance of the batteries. However, I nearly always use a resistor anyway to make sure I'm not blowing the LEDs over time. This is especially true with rechargeable batteries as they have a much lower internal resistance than non-rechargeables and therefore will find it easier to provide an over current to the LED, although this is often compensated for by the lower voltage of NiMhs of 1.2v.

There is a good online resistor calculator for single, parallel and serial LEDs here:
http://ledz.com/?p=zz.led.resistor.calculator

You just need to know the battery voltage you'll be using, the LED voltage and current (which you can usually find from the sellers). LEDs are also usually more efficient at lower currents, so using two LEDs with the same combined total current can provide more light than one LED at the equivalent total current.