Sample code for using adafruit servo shield?

Question

I would like to control 16 motors with a servo shield, however, I have found scant to nothing sample code online. The one I was able to find is...strange to say the least

https://github.com/kachok/arduino-libraries/blob/master/Adafruit_PWMServoDriver/examples/servo/servo.pde

#include <Wire.h>
#include <Adafruit_PWMServoDriver.h>

// called this way, it uses the default address 0x40
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();

#define SERVOMIN  150 // this is the 'minimum' pulse length count (out of 4096)
#define SERVOMAX  600 // this is the 'maximum' pulse length count (out of 4096)

uint8_t servonum = 0;

void setup() {
  Serial.begin(9600);
  Serial.println("16 channel Servo test!");

  pwm.begin();

  pwm.setPWMFreq(60);  // Analog servos run at ~60 Hz updates
}


void loop() {
  // Drive each servo one at a time
  Serial.println(servonum);
  for (uint16_t pulselen = SERVOMIN; pulselen < SERVOMAX; pulselen++) {
    pwm.setPWM(servonum, 0, pulselen);
  }
  delay(500);
  for (uint16_t pulselen = SERVOMAX; pulselen > SERVOMIN; pulselen--) {
    pwm.setPWM(servonum, 0, pulselen);
  }
  delay(500);

  servonum ++;
  if (servonum > 15) servonum = 0;
}

Im used to controlling motors using servo.write, but with the shield, it doesn't seem very intuitive as to how I should control the motors. How does Servomin and Servomax map to 0 degree and 180 degree?

Someone please elucidate!

Answer 1

The 2 values SERVOMIN and SERVOMAX define the pulse length, which tells the servo what angle to go to. The example uses 150 for SERVOMIN and 600 for SERVOMAX. When running the code, the servos travel 180 deg. I changed the code to read:

#define SERVOMIN  262 // this is the 'minimum' pulse length count (out of 4096)
#define SERVOMAX  488 // this is the 'maximum' pulse length count (out of 4096)

and the servo now moved only 90 deg. centered at the same place as the original code.

the tutorial provided by Adafruit describes a way to define the movement by angle:

pulselength = map(degrees, 0, 180, SERVOMIN, SERVOMAX);

found here: https://learn.adafruit.com/adafruit-16-channel-pwm-slash-servo-shield/using-the-adafruit-library

hope this helps

Answer 2

Adafruit's guide for the shield is here: https://learn.adafruit.com/adafruit-16-channel-pwm-slash-servo-shield/using-the-adafruit-library

I'm not sure how much the library you linked and the official one differ. They seem to be used the same way, but you should probably stick with the official one.

You are going to have to use setPWM(pin, on, off) since the arduino is not generating the signals like it would with servo.write(), the arduino is sending commands to a chip on the shield that generates the signals for you.

Adafruit recommends calibrating SERVOMIN and SERVOMAX yourself with whatever brand of servo you plan on using, but those default values should be pretty close.