Add example for writeMicroseconds()

The writeMicroseconds() function is used to mimic the Arduino Servo library writeMicroseconds() behavior.
The writeMicroseconds() function is based on setServoPulse() but uses microseconds instead of seconds. This is to match with the Arduino Servo library writeMicroseconds() behavior.
This example follows what setPWM() example does driving the servo through the range of positions but using writeMicroseconds()
writeMicroseconds() is not expected to be precise due to calculation rounding converting between microseconds and ticks.
New constants were added to simplify changes like the frequency of the PCA9685 chip.

Author: photodude

examples/servo/servo.ino

@@ -31,8 +31,11 @@ Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();
 // want these to be as small/large as possible without hitting the hard stop
 // for max range. You'll have to tweak them as necessary to match the servos you
 // have!
-#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)
+#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)
+#define USMIN  611 // This is the rounded 'minimum' microsecond length based on the minimum pulse of 150
+#define USMAX  2441 // This is the rounded 'maximum' microsecond length based on the maximum pulse of 600
+#define FREQ 60 // Analog servos run at ~60 Hz updates
 
 // our servo # counter
 uint8_t servonum = 0;
@@ -43,29 +46,29 @@ void setup() {
 
   pwm.begin();
 
-  pwm.setPWMFreq(60);  // Analog servos run at ~60 Hz updates
+  pwm.setPWMFreq(FREQ);  // Analog servos run at ~60 Hz updates
 
   delay(10);
 }
 
-// you can use this function if you'd like to set the pulse length in seconds
-// e.g. setServoPulse(0, 0.001) is a ~1 millisecond pulse width. its not precise!
+// You can use this function if you'd like to set the pulse length in seconds
+// e.g. setServoPulse(0, 0.001) is a ~1 millisecond pulse width. It's not precise!
 void setServoPulse(uint8_t n, double pulse) {
   double pulselength;
 
   pulselength = 1000000;   // 1,000,000 us per second
-  pulselength /= 60;   // 60 Hz
+  pulselength /= FREQ;   // Analog servos run at ~60 Hz updates
   Serial.print(pulselength); Serial.println(" us per period"); 
   pulselength /= 4096;  // 12 bits of resolution
   Serial.print(pulselength); Serial.println(" us per bit"); 
-  pulse *= 1000000;  // convert to us
+  pulse *= 1000000;  // convert input seconds to us
   pulse /= pulselength;
   Serial.println(pulse);
   pwm.setPWM(n, 0, pulse);
 }
 
 void loop() {
-  // Drive each servo one at a time
+  // Drive each servo one at a time using setPWM()
   Serial.println(servonum);
   for (uint16_t pulselen = SERVOMIN; pulselen < SERVOMAX; pulselen++) {
     pwm.setPWM(servonum, 0, pulselen);
@@ -78,6 +81,19 @@ void loop() {
 
   delay(500);
 
+  // Drive each servo one at a time using writeMicroseconds(), it's not precise due to calculation rounding!
+  // The writeMicroseconds() function is used to mimic the Arduino Servo library writeMicroseconds() behavior. 
+  for (uint16_t microsec = USMIN; microsec < USMAX; microsec++) {
+    pwm.writeMicroseconds(servonum, microsec);
+  }
+
+  delay(500);
+  for (uint16_t microsec = USMAX; microsec > USMIN; microsec--) {
+    pwm.writeMicroseconds(servonum, microsec);
+  }
+
+  delay(500);
+
   servonum ++;
-  if (servonum > 7) servonum = 0;
+  if (servonum > 7) servonum = 0; // Testing the first 8 servo channels
 }