Data Sheet

Programming Note:

This sketch uses a counter to increase the

brightness of the LEDs. Once the LED nears full

brightness then the counter decreases to make

the LEDs dimmer.

Some of the digital pins (including D9, D10, and

D11, which are connect to snaps and used here)

may be controlled using the analogWrite

()

command. analogWrite() simulates an analog

voltage using pulse width modulation, which

varies the duration of a digital pulse. Here the

LEDs are made brighter by increasing the

duration of the pulse (making the LEDs on for a

longer amount of time), or made dimmer by

decreasing the duration of the pulse.

The value for analogWrite

() can be from 0 (LED

off) to 255 (LED always on). This sketch uses a

maximum value of 30 for analogWrite(), because

the LED brightness would change very slowly for

higher values. Try increasing this value from 30 to

255, upload the sketch to Snapino

, and see how

it affects the LED brightness. You can also adjust

the delay value (currently 30) to make the LED

brightness change faster or slower.

Why do analogWrite

() values of 30 or more make

the LEDs appear at full brightness? Because the

light is changing faster than your eyes can adjust,

and your eyes continue seeing what they have

just seen. This is often called “persistence of

vision”. This concept is used in movie theaters.

Project 16

Varying LED Brightness

Build the circuit and load sketch

Varying_LED_Brightness into Snapino

using

the programming instructions in project 3. The

three LEDs (D1, D2, & D10) continuously vary in

brightness.

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