Technical Details and Applications
The RURB is a general purpose USB interface device that can be used in many kinds
of psychological experiments and in situations where a simple
electrical trigger is needed to go into a computer in the form of an equivalent keypress, via a USB port.
The BUTTON BOXes can be plugged directly into the INTERFACE BOX, for use outside the MRI environment.
The RURB was developed originally for use in Functional MRI experiments. The INTERFACE BOX is attached to the
USB port of a Macintosh or PC computer outside the MRI room. Long ribbon cables (user supplied) are run from the DB-25 pin connector
on the INTERFACE
BOX to the
penetration panel of users MRI room. The penetration panel must have a free DB-25 connector. The BUTTON BOX CABLE is
plugged into the penetration panel on the inside of the MRI room and the BUTTON BOX is handed to the
subject. (Fifteen foot cables attached to the BUTTON BOXes are
sufficient in the MRI rooms where we use them. Longer cables can be supplied if requested. If user cannot supply a DB-25 pin connector through the
penetration panel, the user can rewire the connector at the ends of the cables, as needed.)
IN ADDITION: There is a BNC connector to take an electrical
signal from the MRI scanner itself (generated by the
pulse sequence software, suitably modified by the user, if necessary) and create a USB
keypress. This is used to synchronize and/or record the time
MR images are generated with the stimulus generation software for
psychological experiments. It can be triggered by any suitable electrical
device that puts out a TTL pulse of 2-5V for longer than 2ms. Triggering is on the rising edge of the signal.
NOTE: The response box is merely a collection of momentary
contact switches suitably housed and cabled. It does generate an electrical current when
the button is pressed, and is therefore not a perfectly rf-silent device. However,
there is no polling or other digital circuitry involved; it is less expensive and less fragile
than a purely optical alternative; and there has been no indication that it
has generated any radio frequency signals that have interfered with our fMRI-based experiments. Electro-optical
components within the INTERFACE BOX isolate the BUTTON BOX circuits from any USB-generated rf noise.
UPDATE: 9/01/05 For a number of reasons, we are no longer making this device. Chiefly, we no longer have an NMR researcher who needs these made internally. Although the vast majority of our users made many successful experiments, a few were unable to eliminate spurious noise signals when using the keyboard, despite our best efforts to support them. The spurious signals could have been due to power supply noise, or any number of other issues, but without the facilities to test this directly, it is difficult to say. Going forward, we don't have the time to devote to chasing down these issues, but in the interest of supporting those who want a solution that is 'good enough' for many applications, we're publishing the schematics here. Caveat Emptor!
Schematics
The components of the Rurb consist of a device called an Xkey OEM USB interface, available from PI Engineering. To this, we add a set of opto-isolators. Quite simple to make in any EE lab, and it may suit your needs. Changes which you might consider are to substitute a battery for the power coming from the USB port.
Users can build their own button boxes very simply, or can replace the switches used in the sample
BUTTON BOXes to suit their needs. Of course, in the MR environment, user-built button boxes should be magnet compatible. Our BUTTON BOXes are
plastic, with plastic switch mechanisms that use a minimum of metal.
NOTE on Power Supply
: No external power supply is needed for this product, as the USB interface supplies the necessary power for
operation of the INTERFACE BOX and the BUTTON BOXes.