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Some experiments require accurate timing of the interval between when a
subject sees a stimulus displayed in the CUBE, and when they push a
button in response.
This timer performs such timing. It samples the voltage sent to
one of the video projectors to determine when the stimulus begins, and
checks two other inputs for when a button is pushed. We have
experimented with both wired and wireless versions of the handheld
controller. The wireless one uses the internals of the popular
Bit-CharG radio-controlled car, labeled "Receiver" in the
photograph of the breadboard. The car's controller uses
comfortable buttons salvaged from a TI-99/4A home computer.
A C-language program runs on the AVR Mega8 microcontroller to sample the
inputs and measure the elapsed duration to an accuracy well within a
millisecond. This one-chip computer is highly predictable and
reliable, since no operating system like Windows is running. When
a stimulus-response interval has completed, it then reports the result
over the green RS-232 cable to a conventional PC networked with the
CUBE.
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