Working with Arduino:
Lesson #4: Servos
EGN1007
Learning Goals
Learning Goals: The student will be able to:
1. Build a complete circuit using the Arduino microprocessor
2. Identify important electrical components in a circuit and explain their
use
3. Identify and apply specific elements in “C” code used to run a
program in conjunction with how a circuit is built
Servos
A servo takes a timed pulse and
converts it to an angular position.
How do you communicate the angle at which the servo should turn? The control
wire is used to communicate the angle. The angle is determined by the duration of
a pulse that is applied to the control wire. This is called Pulse Coded Modulation.
The servo expects to see a pulse every 20 milliseconds (.02 seconds). The length
of the pulse will determine how far the motor turns. A 1.5 millisecond pulse, for
example, will make the motor turn to the 90 degree position (often called the
neutral position). If the pulse is shorter than 1.5 ms, then the motor will turn the
shaft to closer to 0 degrees. If the pulse is longer than 1.5ms, the shaft turns closer
to 180 degrees.
Schematic Symbol?
There is no symbol for a servo because it is
part of an EXTERNAL circuit. The servo itself
will be plugged into 3 ports somewhere on
the circuit board, often represented by a 3-pin
header.
Let’s Begin
1. Place the 3 pin header into E5,6, &
7.
2. Plug the servo into the header
3. Run a wire from Analog 9 to A7.
4. Run a wire from the 5V to A6
5. Run a black wire from A5 to the
ground(GND).
Programming our sketch
Let’s define 1 variable as an integer.
Programming our sketch
Just like before we need to set our SERVO as an output.
Programming our sketch
We begin by creating a variable
called “pulsetime” which will record
the time of the pulse that corresponds
to than angular position you want.
Compile and download
Your turn!
Using what you have learned in this lesson
AND the past lessons, write a short program
that controls servo using a potentiometer.
Write your code on the lesson worksheet, draw
the schematic, and explain your code.
Hint: The POT reads values from 0 to 1024 and
the servo only understands values from 0 to
180