For this circuit you need any spare USB cable, one LED, 1 resistor. & tools.
Step 1: Connections of the Circuit...
Connect resistor one end to the longer pin(Anode) of LED with the help of solder (you can also connect them by twisting both the pins), Now we have two pins spare, one pin of resistor and another one short leg(Cathode) of LED.
Step 2: Connections of the Circuit
Step 3: Circuit Testing...
Laptop or Desktop.
Is it glowing?
So we have glowing LED now,
but the question is, we choose the resistor of 100 Ohm, why?
Step 4: Calculation of Resistance
calculate the value.
There is a simple and most significant formula, Ohm's Law.
According to Ohm's law
I = V/R,
I= Current (A) (current flowing through the resistor),
V= Voltage (V) (voltage across the resistor),
R= Resistance (Ohm).
In our circuit, we know…
The voltage supply voltage = 5V.
Voltage across LED = 3V. (Normally LED 5mm runs on 3V).
Voltage dropped by resistance= 5-3=2V.
Current to be flowed through LED = 20mA = 0.020 Amp.
Resistance= V/I = 2/0.020 = 100 Ohm.
Thanks for being on my Instructable.