# 08. Fading LED

The first example of analog output uses a LED to realize a fading LED. It can be managed from the Internet via start and stop commands.

## 1. Circuit

Connect the LED as shown in figure 1:

• positive PIN to the PIN d2
• negative PIN to the PIN GND (Ground).

The long PIN is positive as shown in Figure 2.

## 2. Sketch

Write a sketch K to define:

• the output connection: led::d2
• the commands to control the LED: start, stop
``led :: d2   ``
``d = 50   ``
``start = [led=led+d *,led=0]   ``
``stop = [led=0]   ``
``led==0 -> d=50   ``
``led==1000 -> d=-50   ``

or simply load the sketch with the command

``] load e08_fading_led``

## 3. Try and learn

Try the following commands now:

• `] start`

the brightness of the LED grows (fade in) and decreases (fade out)

• `] pause`

the fading of the led stops

• `] play`

the fading of the led resumes

• `] ??`
``--- Periodic commands``
``led=led+d *``

shows the periodic commands running

• `] trace=1`
``ok``
``] ``
``# led=led+d``
``...``
``]``
``# led==0 -> d=50``
``# d=50``
``]``
``# led=led+d``
``...``
``] ``
``# led==1000 -> d=-50``
``# d=-50``
``] ``
``# led=led+d``
``...``

traces the commands running

• `] trace=0`

ends the tracing

• `] stop`

turns off the led and stops the fading of the led

• `] ??`
``null``

stop command also clears the commands running.

Try replacing the LED with a BUZZER connected to d2. What happens?

## 4. Summarizing

In this lesson you learned:

• how to use a LED
• the commands: load, start, pause, play, ??, trace, stop.