
- 3 -
Figure 2: Interface electronics
The computer interface (Figure 2) uses the parallel printer (Centronics) port on an SGI Indigo work-
station, but is suitable for any machine with a Centronics port. The interface does the standard Centronics
handshaking and passes the eight bit parallel data either to a D/A converter that controls the throttle, or to a
D/A converter that controls the steering depending on the high order bit. The outputs of the D/A converters
are buffered through operational amplifiers connected as Voltage Controlled Voltage Sources (VCVS)
because the D/A converters have insufficient current drive.
The throttle operational amplifier’s output is connected to the the radio’s controls via half of a double
pole double throw switch. The switch disconnects the potentiometer (joystick) and connects the operational
amp, or vice versa if one desires manual control of the radio transmitter. The steering operational amplifier
is connected similarly to the other joystick’s output.
3. The Software (Local Operation)
There are two versions of software used, one for local operation with full motion video and another
for network operation using compressed video. For local operation, the software runs as an X-Window
application. Two windows are used. One is the mouse tracking window, the other is the video window.
The video window is set to be the same size as the mouse tracking window and placed over the top of it.
The mouse is tracked in the hidden bottom window and its scaled (-1,+1) X and Y coordinates are passed to
the program. The program sets its throttle (forward or reverse) proportional to the Y axis position and its
steering proportional to the X axis position. For example, if the mouse is in the upper left corner of the
video window, this is interpreted as turning left, while moving forward. The throttle setting is only valid if
mouse button 1 is pressed, otherwise the throttle is neutral. We have found this is essential to make the car
usable. The central ten percent of the X and Y axes are a dead zone with neutral steering and neutral throt-
tle. The dead zone is to minimize the hand-eye coordination needed to control the car - to stop the car, the
driver simply has to enter this zone.
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