Turning On The Red Light?

I was recently playing with a web program called 123D Circuits where you can make your own circuits and simulate them without having to buy any pieces! This is awesome because I’ve never really known where to buy bread boards and was never so motivated as to Google for them.

This program sort of lets you do whatever you want as long as you use the components they provide. So let’s just do something that all circuit beginners start out doing: lighting up an LED!

I suppose we’re going to need a power source and then an LED:

Basic circuit.

Here’s our basic circuit.

So we’re using a total of 3V as our battery source to power our LED. Why? Just because. Now let’s press the “Simulate” button and call it a day!

Broken LED.


So for some reason our LED exploded which is both annoying but also cool. Good job 123D! Now why would it explode? Most likely it’s being powered too much. In fact, the reason is because there is too much current going through the LED. An LED generally has a max current rating of 20 mA but in this case (assuming it’s a 1 Ohm LED), it’s getting about I = V / R = 3 / 1 = 3 Amps of current. So that’s a little bit too much…

So how can we reduce the current? By adding resistance to the circuit! We can do that by adding a resistor so let’s do that, fire this baby up, and then we can call it a day.

Not working.


Okay this is silly. What could be the problem here? Actually if you speak Resistor, you would notice that this resistor has a resistance of 1 Ohm (you can tell this by reading the color sequence on the resistor; Google is your friend in this case). So ideally if we increase the resistance (to 220 Ohms because that gives us about 13 mA of current), then we are finally done:

Almost done.

Resistance is 220 Ohms.

Cross your fingers!

Working circuit.

And so there was light!


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