Traffic lights on a bridge

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					Traffic lights on a bridge
To use ICT to recreate an effective sequence of instructions using simulation and
control language, based on flowcharts.

To use ICT to model a set of lights which control the flow of traffic across a single
track bridge.

To build and test the new system, changing the variables to achieve a realistic result.

Activity description
The teacher started by explaining that traffic lights are often used to ensure that
vehicles can alternately and safely use a narrow stretch of road. One line of traffic
will be stationary for a fixed period of time while the other line proceeds. Then in a
class discussion, after a visit to a local hump−backed bridge over a canal, the pupils
agreed the sequence of a simple set of traffic lights.

In previous activities the pupils had developed their understanding of a software
package that uses flowchart instructions to simulate inputs and outputs and to
control graphical simulations. They had been given opportunities to map objects to
outputs, sequence instructions and handle inputs in order to manipulate simple
simulations. In this activity the teacher asked the class to create a flowchart
representation of the instructions needed to control the bridge traffic light sequence.

The pupils tested and refined their instructions to achieve a realistic result. They
discussed how control systems are used outside school, not only as simple traffic
lights over a bridge, but as more complex control systems such as for a lift or rail

In this example Daniel has successfully created a linear set of instructions that
accurately implements the appropriate sequence for the two sets of traffic lights. He
has addressed the issue of ensuring that both pairs of lights work in the correct
sequence by testing the sequence and observing the outputs.

This example illustrates aspects of work at level 4 in terms of developing ideas and
making things happen. By experimenting with the timings to achieve a safe flow of

(c) 2001 QCA                               1/8                           designed by keymedia
traffic over the bridge, with both lights on red for a significant period of time, Daniel
has shown that he can create a linear sequence of instructions to control an event in
a predetermined manner, which shows aspects of level 5. In addition, he has
observed how ICT is used outside school.

To help Daniel make further progress, the teacher could give him the opportunity to
incorporate a sensor unit as an input so that the system would respond to the traffic

(c) 2001 QCA                               2/8                           designed by keymedia
Items of work
               Graphic simulation of traffic lights showing outputs

(c) 2001 QCA                           3/8                            designed by keymedia
               Final flowchart showing instructions to achieve desired results

(c) 2001 QCA                                 4/8                          designed by keymedia
               Table showing conditions of lights and outputs with errors

(c) 2001 QCA                              5/8                          designed by keymedia
               Final table showing conditions of lights and outputs

(c) 2001 QCA                           6/8                            designed by keymedia
  Transcript of Daniel's comments on moving from the control of one set of lights to
                                     two sets

(c) 2001 QCA                             7/8                          designed by keymedia
About this entry
Subject:                      ICT
Year:                         7
Key stage:                    3
NC programme of study:        p1a, p2b, p3a, p4b, p5c
Evidence for:                 level 4, level 5
This work shows evidence of: Developing ideas and making things happen,
                             Reviewing, modifying and evaluating work as it
Scheme of work:               06:Control: input, process and output

(c) 2001 QCA                            8/8                           designed by keymedia