Making a flashlight is an excellent opportunity to apply some electronics basic skills. It is a good project for the weekend or even to do in class. However since it is common to use a soldering iron in the execution of the project I do not recommend that children do this without help from an adult.
Here are some instructions that at first glance seem to be complicated but in reality they are quite simple. I theorized a few steps for didactic purposes. Without coiling, let's do it.
Step 1: What You Will Need
•LED ( in my case white)
• Resistor (depend of the LED color)
•Snap conector 9v
•BEP toggle switch
These items are generally cheap and easy to find.
Step 2: Building the Circuit
1.To create the flashlight circuit I chose connect white LED’s in paralel. For this you must understand that all LED’s have two terminals, the small one is negative and the big one is positive. So I soldered all the negative terminals togheter.
Step 3: Calculating the Correct and Choosing the Resistor
2. Each positive terminal were soldered in a resistor. To choose the resistor you will need to know :
•the voltage of the power supply, ie. how many volts will you use to power your LED,
•the voltage supported by your LED in volts,
•the current supported by its LED in amps.
This information will depend of the LED color (table 1). To calculate the correct resistor it is necessary to apply the formula:
R = (Vpower supply -Vled) / I
R= is the resistance in ohms
Vpower supply = is the voltage in volts of the power supply (battery)
V led = is the voltage in volts of the LED
I = is the LED current in amperes
For example, in my case I chose use a white LEDs for the flashlight. Thus, If we substitute the values on the formula we will find
R = (9 - 3) / 0,02
R = 6 / 0,02
R = 300 ohms for each LED
However I couldn't find a 300 ohms resistor só I opted for the 330 ohms resistor is more common to find. So as a said, I soldered a 330 resistor ohms in each positive terminal and connected all the resistors together. The BEP toggle switch was linked on the negative terminal. To complete the circuit I soldered all on the snap conector. Like on the image above.
Step 5: Case
Finally I put all this stuff inside a tube. This step is optional, but for me made possible use the flashlight In the rain. Other possible cases can be made of pipes or a tin of altoids