Add a `writeMicroseconds()` function

[photodude]

• **Describe the scope of your change Add a writeMicroseconds() function for use in libraries that use standard Arduino servo library and want to convert to this breakout board. (currently modifying an ESC library for use with this breakout board)

The function is based on the example servo sketch's setServoPulse() method

• Calculates the PCA9685 chip PWM Frequency from the prescale by reversing the calculations in the setPWMFreq() function
• Calculates the pulse for the PWM based off the input Microseconds
• Includes debug output for calculations based on example setServoPulse() method outputs

• Describe any known limitations with your change.

  • Output is not precise due to the calculations involved (same as the example servo sketch's setServoPulse() method)
  • Output PWM pulse is limited to starting at the beginning 0 value

• Please run any tests or examples that can exercise your modified code.

  • Unit tests are lacking for this new function (sorry, writing Arduino Unit test is beyond my current knowledge base)
  • It should work the same as the setServoPulse() method; but uses the chip frequency not a hardcoded value, and takes microseconds as the input unlike the setServoPulse() method which used seconds.

[ladyada]

hiya thanks for the contribution

before we can merge, please fix up travis so it compiles/passes :) https://travis-ci.com/adafruit/Adafruit-PWM-Servo-Driver-Library/builds/133676811 also please add a short example demonstrating how you expect this function to be used

[photodude]

@ladyada travis is fixed now (I thought I had read over the code better than that before submitting, c'est la vie)

As for an example. I'm rewriting the RB-ENantel/RC_ESC to use the Adafruit PCA9685 PWM servo driver. The RB-ENantel/RC_ESC library currently uses the Arduino servo library to talk to Electronic Speed Controllers (ESC) and all of the functions are dependent on the Arduino servo library writeMicroseconds() by including a writeMicroseconds() function here it makes modifying libraries that depend on the Arduino servo library a simpler process.

function is used by calling pwm.writeMicroseconds(Pin, microseconds); to set the pulse length in microseconds and not ticks. Example pwm.writeMicroseconds(0, 1000); would make a 1000 microsecond pulse on pin 0 of the PWM/Servo driver the library is attached to (0x40).

pwm.writeMicroseconds(15, 2500); would make a 2500 microsecond pulse on pin 15 of the PWM/Servo driver the library is attached to (0x40).

this mimics the arduino servo.writeMicroseconds(1000); method which would write a 1000us pulse to the pin the library instance was attached to.

[photodude]

There is probably a better way to calculate the frequency from the prescale, I just attempted to reverse what was done in the setPWMFreq() function.

[ladyada]

awesome! great work :) please ping us when the example is added

[photodude]

@ladyada I take it from your response I need include something in the code examples folder showing use of this function.

Would it be sufficient if I extend the existing servo example with this new function?

[ladyada]

yep! that sounds good

[photodude]

@ladyada the Servo example is now extended to include writeMicroseconds().

[ladyada]

nice! what hardware did you test with?

[photodude]

@ladyada Tested with an arduino Uno, a Flycolor ESC, a 950KV motor. Was able to correctly arm and control the motor speed.