For the three-speed fan control, use the "u" (step-up), "d" (step-down) and "s" (stop) buttons so that by pressing "u" while stationary or at low or medium speeds would set the motor to low, medium or high speeds, respectively (the speed is increased or stepped-up by one notch each time the u-button is pressed); the opposite is to happen when the "d" button is pressed (while turning at low, medium or high speeds, the motor should step down to stationary, low or medium speed, respectively); u/d is to produce no effect at high-speed/stationary-state (respectively); s has to stop the fan.

Expected: machine state design, state equations and ladder diagram (with machine outputs).

Alex

Hint for those who missed the class: if you would just replace x, y and z by u in the fan-example in the notes, it would not work well because by pressing the u button from the stop-state would always set the machine to the high-speed motion with just a quick skip through the low and medium speed states; "wait states" could be added in which the machine would wait for the button being held (u) to be released.

Additional Hints:

My solution uses 8 states.

A common mistake is to have a state with two out arrows with the same condition of nothing is pressed

The design with only the u-button the way we showed it in class had a wait state before the low-speed state in which the machine would wait for us to release the u-button before getting the motor moving; if both, the low-speed and the wait state before it are connected for the low-speed operation, the motor would start moving on the event of pressing, rather than releasing, the button (this is something to consider at the very end of the design work when the machine outputs are generated)