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home > Art Projects > Jim Jenkins "The Little Chair"


Guy Marsden

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Jim Jenkins
August 2002
"The Little Chair"

Exhibited at:
Museum Of Neon Art
Lost & Found: A Group Exhibit of Neon and Kinetic Art"
August 28, 2002 - March 2, 2003

This is a small child's chair like those used in grade school.
As you approach it, the chair begins to rotate clockwise, and
then after a few seconds the words "SIT STILL" appear floating
above the chair in red letters, these words change to "BE STILL"
and then "AM STILL" over time (about a minute) then the chair
slows to a stop.
  See a QuickTime movie(381K) of it in action!
(download the QuickTime player here)

When Jim described what he had in mind for this chair, I was able
to refer him to a surplus source for powerful variable speed motors
and driver circuits that can ramp up the speed.
I then built him a timer circuit that senses the presence of a person
(with a passive infrared motion sensor) and starts the motor and
then the light stick that shows the text.
Here's a view inside the timer that sits in the base:

 That little gold chip in the middle of the beige circuit board
is a PIC microcontroller - a complete 12 bit computer
that runs at 4 MHz with 1K of memory!  I programmed the
timing sequence into it and it then turns on the big black
relay (lower right) that powers the motor.

I have never built a Light Stick before, it works on the principle
of persistence of vision.  A row of very bright red LED lights
is programmed to blink on and off in such a way that as they
move rapidly across your field of vision an image (or text) is formed.

Here is the electronic circuit that I built, and the housing
that Jim made for it from PVC pipe:


The close-up of my circuit above shows the PIC microcontroller
that contains the programmed light pattern.  The small device
on the wire at the bottom is a Hall Effect Sensor.  It senses a magnet
mounted to the structure that triggers the light to turn on at the
11:00 position above the chair.  This ensures that the text always
starts in the same spot as the chair rotates clockwise.
Jim cleverly mounted the magnet to an adjustable arm so that
he could set the start point of the lettering accurately:

Since the light stick rotates with the chair, Jim had to design a
commutator that would pass the 12 Volts DC that powers the
light stick to the rotating section.  The power comes in
at the bottom via the colored wires and travels through
brass strips that press against the rotating rings mounted
to the shaft that spins the chair.  Wires then feed up inside
the tube from the rings to power the LEDs.

See a QuickTime movie(381K) of it in action!
(download the QuickTime player here)

Jim teaches art at Cal State Fullerton in California,
contact him at: jjenkins@fullerton.edu

See more of Jim's work on his web site at:
http://www.jimjenkins.net

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