# Manual and Automatic Traffic Lights

And something else, which we'll start with before trying to regulate our traffic.

We'll use LEDs (Light Emitting Diode): 1 red, 1 yellow and... ?!?!
yes, 1 green.

In the first part every LED will be gradually turned from off to on and viceversa.

After that, the traffic lights:  just one LED on.

We need following stuff:

• Arduino Duemilanove Board;
• 3 LEDs;
• 3 of 100$\Omega$ resistors;
• a nominally 4,7$k\Omega$ trimmer resistor or potentiometer, to change the amount of voltage (every kind of volume regulator is a potentiometer);
• some wires.

Quick Quiz!
Why do we put resistors in series to LEDs and before them?

Exceeding voltage - better current - could definitively damage a LED: using a resistor we oppose a kind of wall to the power supply.
In our case 100$\Omega$ is little but enough value.

To be sure, read LEDs datasheets and check the maximum voltage-current they can support (and set a lesser one to work).

Now see the picture above: this configuration is quite perfect for all goals.