This project show you how to do a flashlight using a cell phone battery
Step 1: Part List
For this Project you will need :
High Brightness LED (1W) 1
Universal Board (5x5cm) 1
Cell phone Battery Push button switch 1
Single Row Headers female 1
Single Row Headers male 1
Step 2: Circuit
The resistor is determined by ohm's law, this mean that your resistor depend on of the power of your led. e.g ,
for a led of 1W of power with a cell phone battery of 3.7V (Nominal),Your minimum value of resistor will be :
V=I*R then P=(V^2)/R
where P = 1W and V= 3.7V (note: batteries have a maximum voltage of 4.2 volts be careful)
R=((3.7V)^2)/ 1W=13.69 ohm
Then the current will be :
I=V/R , I= 3.7 volts/13.69 ohms =270mA;
In my case I use a 3W Led
R=(3.7^2)/3W =4.56 ohm, I=811mA,
I recommended to use a resistor with some more ohms because the battery usually have 4.2 volts then I use a 6.2 ohm resistor with power dissipation of 2W.
Step 3: Soldering the Circuit
The push button is toggle push button
Cut the female headers and solder it to the battery
The board is designed to connect directly to the battery
Step 4: Testing
After a few minutes of working I noticed that the led need a dissipator
note: the battery has to give more of current that the circuit requires, this battery give around 2500mAh, to know more about battery parameters see this video https://www.youtube.com/watch?v=cxkVxi9P0EA
I expect your feedback.
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Please be positive and constructive.