Servo Motor - How to Control Servo Motor

Tutorial Video

Hardware

• PHPoC Blue or PHPoC Black
• Micro USB to USB Cable (to upload source code to PHPoC Device)
• Servo Motor
• Jumper wires

About Servo Motor

Stardard servo motor is used to control of angular (usually between 0 and 180 degrees). The servo motor used in this example includes three wires:

• VCC wire.
• GND wire.
• Signal wire (receives the PWM control signal from controller).

How the servo motor works: servo motor can be controlled by generating PWM signal to signal wire of servo motor. The motor sepcification defines cycle time, minimum and maximum duty cycle.

• If generating PWM signal with minimum duty cycle to signal wire, the servo motor rotate to 0 degree.
• If generating PWM signal with maximun duty cycle to signal wire, the servo motor rotate to 180 degree.
• If generating PWM signal with duty cycle between minimum and maximum value to signal wire, the servo motor rotate to position that is proportional to duty cycle.

How to control servo motor:

• Harware timer and software timer on PHPoC device can generate PWM signal. Therefore, It just needs connect the HT pin (or selectable IO pin if using software timer) of PHPoC device to the signal wire of servo motor. And then use hardware/software timer to control servo motor.

Wiring Diagram



Quick Steps

Source code of this example is a part of PHPoC Support Packet (PSP). You need to:

• Download PHPoC Support Package.
• Upload example\p4s\01.php_task\03.ht_pwm_servo to PHPoC Blue/Black.
• Click "Run" button on PHPoC Debugger.

If you use PHPoC for the first time, see How To Use PSP.


Source Code

Source files includes:

• init.php: this file is run when PHPoC system is powered or reset. It is used to specify which file is run is system loop.
• task0.php: this file is run in system loop of PHPoC devices.

init.php

This file is run when PHPoC system is powered or reset. It is used to specify that task0.php is run is system loop.

<?php

system("php task0.php");

?>

task0.php

[Full Code]

<?php

if(_SERVER("REQUEST_METHOD"))
 exit; // avoid php execution via http request

include_once "/lib/sd_340.php";

define("PWM_PERIOD", 20000); // 20000us (20ms)
define("WIDTH_MIN", 600);
define("WIDTH_MAX", 2450);

echo "PHPoC example : P4S-34X / HT / Tower Pro SG92R Micro Servo\r\n";

ht_pwm_setup(0, WIDTH_MIN, PWM_PERIOD, "us");

echo "CCW ";
for($angle = 0; $angle <= 180; $angle += 45)
{
 echo $angle, " ";

 $width = WIDTH_MIN + (int)round($angle / 180.0 * (WIDTH_MAX - WIDTH_MIN));
 ht_pwm_width(0, $width, PWM_PERIOD);

 sleep(1);
}
echo "\r\n";

echo "CW ";
for($angle = 180; $angle >= 0; $angle -= 45)
{
 echo $angle, " ";

 $width = WIDTH_MIN + (int)round($angle / 180.0 * (WIDTH_MAX - WIDTH_MIN));
 ht_pwm_width(0, $width, PWM_PERIOD);

 sleep(1);
}
echo "\r\n";

?>

[Explanation]

Source code of this file does:

• Setup and initialize HT0 timer to generate PWM signal.
• Increase/Decrease angle by 45 degree (to rotate motor in counter-clockwise/clockwise).
• Print rotated angle to PHPoC Debugger's console.
• Calculate PWM duty cycle based on angle value
• Generate PWM signal to control servo motor

See Also

• Servo Motor - Controlling Servo Motor from Webpage using Hypertext.
• Servo Motor - Controlling Servo Motor from Webpage with Image.
• Servo Motor - Controlling Servo Motor via WebSocket with Graphic UI.

Other Resources

• PHPoC System Files
• How PHPoC System Works
• How To Use PHPoC Support Package