Description

This is a cross-platform Python library for the USB Griffin PowerMate (don't think it will work with the Bluetooth version). It is tested to work on both Windows and Linux. While it is two completely separate implementations, they have the same interface. Both rely on asyncio.

Picking a Device

Multiple PowerMates can be used at once. The PowerMate class constructor requires a path to the device. On Linux this will be something like /dev/input/event15. On Windows it will be something horrible like \\?\hid#vid_077d&pid_0410#6&1c38037f&0&0000#{4d1e55b2-f16f-11cf-88cb-001111000030}. Rather that type the path directly, you can use PowerMate.enumerate() which returns a list of PowerMate device paths.

Callbacks

This library works on a callback system. The PowerMate constructor takes callback functions for when the knob is turned and when the button is pressed (or released). These callback will be called on an asyncio event loop. The turn_callback should take a single parameter that will be an integer number of ticks the knob has turned. Postive means clockwise and negative means counter-clockwise. The button_callback takes a boolean that is True when the button is pressed and False when it is released.

Example

from powermate import PowerMate

def on_turn(amount):
  print(f'Turned: {amount}')

def on_button(pressed):
  if pressed:
    print('Button pressed')
  else:
    print('Button released')

paths = PowerMate.enumerate()
if not paths:
  print('No PowerMates detected')
else:
  powermate = PowerMate(
      paths[0],
      turn_callback=on_turn,
      button_callback=on_button)

LED Control

The PowerMate has a somewhat controllable blue LED in it. It can either be solid on or pulsing. When it is solid, you can adjust the brightness. When it is pulsing, you can adjust the speed.

To turn it solid on, call powermate.set_led_solid(brightness) where the brightness is 0-255 (default: 128).

To cause it to pulse, call powermate.set_led_pulse(speed, table, when_sleeping). Speed is from -255 to 255. 0 is its default speed (also 1 and -1). Positive numbers multiply its default speed (2 is twice as fast, 3 is three times as fast, etc), and negative numbers divide its default speed (-2 is half as fast, -3 is a third as fast, etc). The table is 0-2, but I haven't noticed any difference. when_sleeping is a boolean that controls if it should continue to pulse when the device is suppose to be asleep (violating the USB power management standards) or whether to go into low-power mode.

asyncio Event Loop

The PowerMate class requires an asyncio event loop to function. In the Linux version, the events are polled on this event loop. In Windows the events are polled on a thread, however in both versions the callbacks are called on the event loop. By default PowerMate will use the current event loop when its constructor is called. However, if you wish to specify another event loop (perhaps one that is created but not started when PowerMate is constructed that will be run on a separate thread), you can pass it to the loop parameter to the contructor.

Shutting Down

Calling powermate.close() will disconnect from the device and prevent further event callbacks from being called.