powermates

[ibi sum]

On Wed, May 27, 2009 at 6:38 PM, M-.-n <nostromo at arkaos.net> wrote:
> That's great. Is it using HID/Joystick API or is it custom ?
> What's the rotation you have to achieve to get the whole scale by default ?

>From $(LINUX_SRC)/drivers/input/misc/powermate.c, the following
enlightenment can be attained:

/*
 * A driver for the Griffin Technology, Inc. "PowerMate" USB controller dial.
 *
 * v1.1, (c)2002 William R Sowerbutts <will at sowerbutts.com>
 *
 * This device is a anodised aluminium knob which connects over USB.
It can measure
 * clockwise and anticlockwise rotation. The dial also acts as a pushbutton with
 * a spring for automatic release. The base contains a pair of LEDs
which illuminate
 * the translucent base. It rotates without limit and reports its
relative rotation
 * back to the host when polled by the USB controller.
 *
 * Testing with the knob I have has shown that it measures
approximately 94 "clicks"
 * for one full rotation. Testing with my High Speed Rotation Actuator
(ok, it was
 * a variable speed cordless electric drill) has shown that the device
can measure
 * speeds of up to 7 clicks either clockwise or anticlockwise between
pollings from
 * the host. If it counts more than 7 clicks before it is polled, it
will wrap back
 * to zero and start counting again. This was at quite high speed,
however, almost
 * certainly faster than the human hand could turn it. Griffin say
that it loses a
 * pulse or two on a direction change; the granularity is so fine that I never
 * noticed this in practice.
 *
 * The device's microcontroller can be programmed to set the LED to
either a constant
 * intensity, or to a rhythmic pulsing. Several patterns and speeds
are available.
 *
 * Griffin were very happy to provide documentation and free hardware
for development.
 *
 * Some userspace tools are available on the web:
http://sowerbutts.com/powermate/
 *
 */