We will make a Rechargeable LED Head torch like the ones we see on TV and on the internet like this one in the picture. Ours may not look so fancy, but it will give a very bright light to allow reading in complete darkness, and won't cost any where near as much as the ready made ones....and best of all..... it will have its own dimmer, so that we can control its brightness!!
So let's begin.
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Step 1: The Items We Will Need to Build Our Rechargeable LED Head Torch
We will need :-
1. A One watt LED diode as shown in the picture. These are available on EBAY for approx Rs.150 for 10 pieces. So one piece costs Rs.15. (Indian Rupees). The LED is already mounted/soldered on its own heatsink, which saves us some time as we don't need to solder it ourselves. The one we use here is a 3 Volt (300mA -milliAmpere) type.
2. A small round plastic container to house our LED bulb and Lens. (I paid Rs.2.50 for the round one which I bought from a local plastic-containers shop in Mumbai.)
3. A small LED Lens reflector collimator to focus our light beam. I have used a 40 Degree focus Lens.
This lens helps to concentrate the beam of light onto the desired area. The lenses are available on ebay.
You may refer to this link :-
I already had spare lenses/reflectors from a broken LED Light fixture at home and have not bought from the above link. (No endorsements to be implied).
Each piece of lens should cost approx Rs.20. The same lens is available in shops on Lamington Road for Approx Rs.3 but one has to buy atleast 300 pieces. So its your choice........
4. A portable USB power bank like the one we use to recharge our phones on the go. I have used a cheap 2600 mAH one which I bought for Rs.130 from around the Crawford market area.
5. A small plastic box to house our dimmer circuit. ( In fact if you don't need the dimmer circuit then the process becomes easier for you.) I will explain this part in the following steps.
6. A piece of wire to connect everything together and power up the torch.
7. A piece of Belt to make the Head Band (maybe canvas...maybe nylon..... maybe elastic.....the kind we use around our waist to hold up our trousers :) . You can even use a piece of ribbon from a discarded I-Card ( Identity Card ). The cost should be around Rs.20 for a metre.
8. A discarded USB wire. This we will use to power up our torch from either a USB powerbank or from a USB Mobile charger.
9.Some Resistors : One 6.8 ohms resistor or close (1/4watt or 1/2 watt). One 47 ohms resistor or close (1/4watt or 1/2 watt) and one 4.7K ohms potentiometer to use as a dimmer. Also one knob to fit on the Potentiometer.
10. Some Velcro to fasten our head band around our head.
11. A small piece of perforated PCB board. It will cost Rs.5 for a piece of approx size 1.5 inches X 2 inches. You get them on ebay. I bought mine from Lamington Road.
12. Small hinges from a broken pair of Spectacles/eye glasses/goggles/glares. The LED once mounted onto this small hinge gives it the ability to tilt up and down and helps to direct the beam of light either closer to us or further away from us. (More evident in the video).
Step 2: This Is the Circuit Diagram for the Dimmer.
The diagram is self explanatory.
I have not used a switch in the actual build as it was not needed. But you may add one if you so feel inclined.
Now for some calculations :-
Since we are powering up the 3 Volt LED with a 5 Volt USB powerbank, we need to get rid of the excess 2 volts coming in( or else our LED will get damaged over a period of time). So we will use a resistor to get rid of this extra 2 Volts. To calculate the amount of resistance required , read the explanation which follows :-
The main calculation is :
Since we are powering up the 3 Volt LED with a 5 Volt USB powerbank, we need to get rid of the excess 2 volts coming in i.e. 5 volts from the battery(powerbank) minus the 3 volts which the LED needs, is = to 2 volts(which is the excess voltage that we need to get rid off).
So 5 - 3 = 2 volts.
We then divide this 2 volts by the LED's required current in milliamperes (mA). For our LED the mA is 300mA. This value is provided in the data sheet which comes with the LED.
So 2 volts divided by 300 mA
i.e 2 / 300 = 0.00666
we multiply this answer by 1000
i.e 0.0066 X 1000 = 6.66 or 6.66 ohms.
So the resistor we need to put between the 5 volt battery and our LED is a 6.6 ohms resistor (The standard value available is 6.8 ohms) or near about to drop the 5 Volts to the required 3 Volts..
There are some Android apps which simply this calculation for us.
"LED Resistor Calculator" available on the Google Playstore for FREE, is a nice app to help with the calculations.
Can someone explain this part :
I have used 2 more resistors ( The 4.7K variable Potentio for dimming down the LED and the 47 ohm resistor) in my circuit. This is because when I measured the Current through the circuit I found it to be around 500 milliAmperes when switched on, and since my LED was rated at 300mA I experimented with additional resistors..... till the 47 ohm one took the mA down to around 250 mA.
Step 3: The Final Appearance
If you do not need the dimmer then you can simply install an on-off switch between the battery and the LED light.
But you will need to install one 56 ohms resistor before the LED.
Will add a Breadboard drawing soon, to help in prototyping/testing the circuit.
Step 4: Update : Added the Bread Board View
I have added the bread board view as promised. It was tested in http://123Dcircuits.io
here is the link
Let the page there load....it takes a little time....then press the "Start Simulation" button......turn the potentiomer knob using your mouse......and see the LED gradually light up !! Amazing !.....no ?? :-)
Another great website for circuit design and bread boarding is http://fritzing.org/
Please note that the Battery Pack used in the bread board design is 4.5 Volts instead of the 5 Volts from a USB powerbank. The 4.5 Volts work but the light will be slightly dimmer.
Also note that the actual LED used in the Torch/Headlight is a 1 Watt Luxeon type rated at 3 Volts and 300 milliamperes approximately. Even if the one you get and use is a 3.3 Volts 350 milliamperes type, this circuit will work perfectly.
So go ahead and make it.
If you need any more information feel free to discuss and ask questions. I will answer them, as well, as I can.
Thanks for reading.