Fix and improve pulse width range by rileyjshaw · Pull Request #24 · arduino-libraries/Servo (original) (raw)

Different servo models can accept a wide range of pulse widths. Even different servos of the same model might vary a bit. Currently, the Arduino Servo library has a severely restricted hard limit on the pulse widths that can be sent to servos. Specifically:

• Minimum pulse width must be between [32, 1052].
• Maximum pulse width must be between [1888, 2908].

Many popular servos have min/max pulse widths that fall in that unavailable range between (1052, 1888). For instance, the Parallax Feedback 360° High-Speed Servo operates between [1280, 1720].

Before this commit, each instance of Servo stored their min and max values as int8_t. Since that only leaves room for values in the range [-128, 127], it can't store meaningful servo pulse widths, which are typically in the ~[1000, 2000]µs range. To compensate, min and max store the distance from the default values, divided by 4…

There are two problems with this:

• The first, mentioned above, is that you can never stray more than 512µs from MIN_PULSE_WIDTH and MAX_PULSE_WIDTH.
• The second is that unexpected and unnecessary rounding occurs.

Simply storing min and max as uint16_t and using the values directly solves this problem, and reduces the complexity involved in working around it. This commit makes the library faster, and allows it to work with a wider range of servos. It also fixes some subtle bugs where the minimum value was hardcoded to MIN_PULSE_WIDTH.

Tested on an Arduino Uno with a Tower Pro Micro Servo SG90, and a Parallax Feedback 360° High-Speed Servo.