Making the LED Torch is one of the easiest electronics projects around. What’s more when properly finished it can be a really practical and useful item. It’s also a great starting point for anyone setting out on their journey into the world of electronics. For this reason we have included some background information on the components used.
Things have moved on from the days when small lamps were the mainstay of torches.
Now LEDs are everywhere, they are efficient and extremely long lasting. It is worth remembering though an LED is a diode and needs to be connected the correct way round. The LED has two leads designated anode and cathode. For the LED to illuminate the anode needs to be connected towards the positive side of the supply and the cathode lead needs to connect to the negative side of the supply. Don’t forget our supply here comprises of three series connected 1.5V batteries.
It is best to check the manufacturers data sheet to determine which lead is which, however, the longer of the two leads is normally the anode. A further point to consider is the LED needs a few volts to work. This voltage is known as the forward voltage Vf and for the LEDs used here is 3.2V. The LED current is 20mA, as 3 LEDs are connected in parallel the total current is 60mA. The purpose of resistor R1 is to limit the current to the LEDs, thereby ensuring they do not exceed their current rating. With this in mind the resistor value is calculated to be 22 Ohms. For interest, this was done by first working out the voltage drop across R1 as follows:-
Battery voltage 4.5V – LED Vf 3.2V= 1.3V
From Ohms Law the value of R1 = 1.3V / 60mA =21.6 Ohm.
The nearest available resistor value is 22 Ohm.
Anyway, that’s enough of the theory – hope this useful and good luck with this project.