Using Hobby Servos with the Arduino

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© 2012 David Hall

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wires to power & control servo

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red = 5V

black = Gnd

white = signal

output shaft

servo components

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1. small DC motor2. gearbox with small plastic gears to reduce the RPM and increase output torque3. special electronics to interpret a pulse signal and deliver power to the motor

types of servos

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continuous rotation

pulse tells servowhich way to spin & how fast to spin

pulse tells servowhich position to hold

standardcan only rotate 180 degreescan rotate all the way around in either direction

Arduino programming

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void loop() { digitalWrite(3, HIGH); delayMicroseconds(1700); // hold pin 3 high for 1700μs or 1.7ms digitalWrite(3, LOW); // hold pin 3 low for 20ms delay(20); }

these lines of code make the servo go full speed counter clockwise

time (milliseconds)

volta

ge (V

)

5V -

0V -

20ms

full speedclockwise

full speedcounter clockwise

pulse width varies between 1.3ms and 1.7ms

pulse width(μs)

servo action

1300 full speed CW

1400 ½ speed CW

1500 stopped

1600 ½ speed CCW

1700 full speed CCW

speed not linear with pulse duration

wiring servo to breadboard

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Since the servos will likely be hooked up for a while, it is worthwhile to keep the wiring tidy, cutting short jumpers from the power bus.

The red wire from the power bus should go back to Vin or 5V, and the black wire should go back to Gnd.

playing around with programing

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“for” loop executes 200 times i = 0, 1, 2, 3, 4, . . . 199

void setup() { pinMode(3, OUTPUT); }void loop() { int i; for (i=0; i<200; i++) { digitalWrite(3, HIGH); delayMicroseconds(1300); digitalWrite(3, LOW); delay(20); } delay(1000); for (i=0; i<400; i++) { digitalWrite(3, HIGH); delayMicroseconds(1700-i); digitalWrite(3, LOW); delay(20); } }

this for loop causes the servo to go from full speed CCW (pulse width = 1700ms) to full speed CW (pulse width = 1300ms)

create a square wave with a pulse width of 1300ms followed by a 20ms pulse

wait one second