Task 7

This task extends task 6 so that the buggy repeats the forward and reverse path.

The worksheets are the prime parts of the design and the first thought  is to connect the output stub from the reverse worksheet back to the start stub of the forward worksheet. However, this locks the system and there is no way of getting a start pulse to the forward worksheet.

An input pulse ( OFF to ON to OFF) is needed to start the first forward worksheet.

A solution is shown in the above figure.

An output from a switch is connected via an OR gate to the forward worksheet. Another output from the timer is connected to the other OR input. The timer is set to have a delay of one second.

An output pulse originates from every worksheet when it finishes its running and this is delayed by one second before going to the OR gate. This is needed by the icon system.

This means that the first worksheet is started by the switch and it is restarted by the delayed timer pulse when the last sheet is finished.

The timing diagram shows these pulses.