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This circuit is a Digital Radar
Speedometer. It allows us to evaluate the speed of any
object moving, especially cars and other vehicles. The
speed is calculated in kilometers per hour (KPH). Its
display has three digits. This radar works with the
laser reflexion. It sends laser radiation to the object
and this object reflects the laser radiation to the
radar. To evaluate the speed of a vehicle, we must be in
front of it. In other words, the vehicle must come in
our direction. The front of the radar must point the
front of the vehicle. The radar has the shape of a
pistol. In this radar, it has a laser LED and a laser
diode. Both have a lens.
The laser LED can send a spot of light
to a distance of 90 m (295 ft). It's very important that
the distance range of the laser LED is 90 m, if not, the
speed will not be calculated properly. The laser diode,
which receives the light signal by the laser LED, must
be able to detect the light which is same color as that
emitted by the laser LED. The laser diode and the laser
LED must be placed one beside the other. They are
protected by a tinted pane. They must be placed at the
front of the radar and point the outside. The radar is
powered by a 9V battery and it has a SPST switch to
control its power state.
The display, or the speed indicator, is
placed at the rear of the radar, just on the right of
the overload LED indicator. All the logic components of
the circuit must be of the 74AS series and TTL type.
Because they have short time of response (less than 1.7
ns) and have high frequency supports (more than 200
MHz). The radar can evaluate the speed of an object
moving between 0 to 999 km/h. After this speed, the
overload LED indicator will turn on and the "999" will
still displayed. The radar displays the speed during 3
seconds, after this time, it displays "zero" (0). |
