provide a way to turn off a Servo

[dhalbert]

Servo doesn't have a way of setting the duty cycle to zero, so that the servo becomes unpowered completely. In Arduino land, detach() does that, because it removes the connection to the (hidden) pwm object (if I understand correctly).

@caternuson was trying to translate the first example here: https://learn.adafruit.com/analog-feedback-servos/servos-as-input-devices and encountered the API differences.

Proposal: add a turn_off() method, which sets the PWMOut duty cycle to zero. Setting the .fraction to any value after that will repower the servo to some non-zero duty cycle.

Tagging @tannewt, @TheKitty, and @ladyada here for any comments they may have.

[ladyada]

yep agree. this is because 'zero' in servo land is 0.5ms pulse, not actually off

[caternuson]

Or via an enabled property?

>>> servo.enabled
True
>>> servo.enabled = False  # turns it "off"
>>> servo.enabled = True   # turns it back "on"

[dhalbert]

If there's an .enabled property, would setting .fraction re-enable it? That could be fine, but it might be unexpected. Or if could ignore setting .fraction if it's disabled, but I'm not sure I like that, because .enabled seems like a general thing that could apply to more than Servo, but I'm not sure it makes sense to add to everything in this library.

[ladyada]

i think no, you should be able to have enabled on/off while changing .fraction without it moving. once its disabled, it should not move!

[tannewt]

FYI, Motor does this with None rather than separate state.

[JohnOmernik]

IS there any update on this. This is a big difference between the Python2 Adafruit libraries and the Circuit Python Python3 libraries. We need a parity in features, or at least a work around.

[JohnOmernik]

What about allowing -1 to actuation range as the angle? 0 is no angle, -1 is off with no change?
If anything other than -1 to actuation range then throw an error.

From the angle_setter

if new_angle < -1 or new_angle > self.actuation_range:
raise ValueError("Angle out of range")
elif new_angle == -1:
# Insert code to set pwm.(channel, 0, 0)
else
self.fraction = new_angle / self.actuation_range

This would allow us to simply issue an angle command, and then issue a -1 without changing the last angle set. It also doesn't "disable" or anything the servo, it's just ready for the next command.

[ladyada]

added in #27

[caternuson]

fixed by #27