LEDs

LIGHTING LEDs

light-emitting diodes

To make a LED light a positive (+) voltage needs to be applied to the Anode and a negative voltage (-) needs t be applied to the Cathode. Do not forget to to add a 470 ohm resistor!!!

So far you have been connecting the Cathode to the negative side of the power supply abd the Anode to a pin on the STAMP. When the pin goes HIGH (+) the LED lights up. When the pin goes LOW (-) the LED does not light because there is no power going through it.

This works fine but one pin is used for each LED. What if you could contol four LEDs with less than four pins (outputs)!!!

Try this to start. Use a 220 ohm resistor on each pin. This means that each pin will always have at least 220 ohms resistance going to the LED. If you do not use at least a 220 ohm resistor, the LED might have too much current/voltage going to it and be damaged.

Make pin1 HIGH and pin2 LOW. The led will light up. What do you think will happen if pin1 is LOW and pin2 is HIGH? Try both HIGH and both LOW. Take notes!!!

Now try two LEDs between two pins. Try all HIGH / LOW combinations. Make a table like the one below and fill in for LED. Give each LED a number. Write ON or OFF.

PIN1	PIN2	LED1	LED2
HIGH	LOW
LOW	HIGH
HIGH	HIGH
LOW	LOW

Tune in next week for another lesson.

Is it next week yet?

Now we will look at more LEDs than pins used.

As you can see, each pair of PINS has a pair of LEDs.
Three PINS gives us three pairs of LEDs.

Now we need to add a way to tell if wires are connected or not connected on the drawing. If there is a DOT where two lines cross, the wires are connected. An electrical drawing is called a schematic.

For our last experiment we will use four PINS and 12 LEDs!!!

Make a table like the one above and see what happens. This can be expanded to as many PINS as you want.
How many LEDs can be controlled with five PINS or six PINS.