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904 Dial Use

Normally this is very simple to use:

  • Connect the dial device to the interface (either through a bundle or not)
  • Connect the interface to the computer (via USB)
  • Spin the dial back and forth to set calibration (LEDs will blink until the calibration is complete)

You will get one of two responses based on the way your 904 is programmed:

Action Joystick output
Rotate clockwise (CW) advance to the right
Rotate counterclockwise (CCW) advance to the left
TTL trigger Joy button 1
Optical Trigger Joy button 1

Action Keycode output
Rotate clockwise (CW) t
Rotate counterclockwise (CCW) b
TTL trigger 5
Optical Trigger 6

LED Indicators During Use

In either dial mode, most of the 904 LEDs only respond during the calibration period, described in the next section.

The left-most LED indicator will blink briefly if an optical or TTL trigger is received.

Initial Setup and Calibration

Any time you change the optical connections you should begin by disconnecting the USB cable. Then you can add a removable bundle, reroute the optical cabling, or connect the DIAL directly to the interface. But always make the USB cable connection last. When the USB cable is connected it enters a calibration period during which:
  • first: the first two LEDs will blink
    • at this time you should spin the DIAL back and forth until
  • second: they will stop blinking,
    • at this time you should put the dial into the position you want to be taken as zero
  • third: the LEDs will blink in succession from right to left
    • at this end of this pattern the zero position is read

It is a good idea to run through this process once or twice to get familiar with how it works, both with and without a removable bundle connected.

Checking the Joystick Output

The quickest way to check the joystick output for most users is to open the Windows game controller control panel. This will let you see the cursor move back and forth in a diagnostic window when you turn the dial. Once this is seen you can confidently proceed to read the joystick output in your programmed task.

Checking the Keyboard Output

Because the keyboard output is just like what a standard USB keyboard issues, you can check this quickly by opening any text editor and turning the DIAL.


There are two main ways that the dial can misbehave:

A mechanical/optical issue can come up during use if the rotation of the dial is accompanied by an off-axis pressure or force. This might be something severe like the dial being dropped to the floor after initial setup, but it also could be something less severe like it being tipped to one side so that the subject is pressing the dial to one side as they rotate it. If you are having this kind of issue with any regularity the first step in troubleshooting it would be to set it up on a benchtop and reproduce the issue by intentionally rotating it in "odd" ways -- in this way you may find that it can be used reliably as long as a particular type of handling is avoided.

The second kind of malfunction would be a general USB or firmware issue. The most common example of this is that the initial calibration might not be good, in which case you should see the problem right away, or at least within two full dial rotations (so it is wise to perform two full rotations right after the calibration). But if you see some other malfunction in the output, and have ruled out the mechanical sources, then we recommend leaving the optical components connected and just unplugging and re-plugging the USB cable in. This will cause the device to reset and you will need to do the gain calibration step. This is something which should only occur rarely if at all.

In no case should you leave the USB cable connected while connecting or disconnecting the optical components (the dial or the bundle) -- doing that may cause unpredictable and badly behaved USB transmissions which may freeze the USB subsystem.
Topic revision: r2 - 18 Apr 2023, BenDugan
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