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TOllbooth gate
Explanation
There are four inputs and four outputs for the tollbooth gate. We have the open pushbutton, close pushbutton, open limit switch, and close limit switch. For the outputs you have the motor open, motor close, gate open, and gate closed. Along with the inputs and outputs, you have the four states, opening, open, closing, and closed. Then you have Qa and Qb which are the number representations of the physical actions and reactions. So essentially, you hit the open pushbutton and the gate opens until it hits the open limit switch where it stops and waits. When you hit the close pushbutton the gate begins to move down until it hits the close limit switch where it will remain until any further action.
Multisim
VEX
Conclusion
We started out by identifying the different inputs and outputs and figuring out their exact purpose. Then we created the state graph from which we realized that the tollbooth design was going to require four states with the two state variables being Qa and Qb. After the state graph, we completed the state transition table from which we derived our input and output combinational logic expressions. Using a little bit of Boolean algebra, we simplified the expressions, making life much easier. Using our newly simplified expressions, we simulated the design in multisim. Using the mulisim blueprint, we breadboarded the circuit and connected it to the VEX tollbooth test fixture. After loading the circuit onto the breadboard we were able to physically test our design and verify that it worked as expected. Unfortunately, we were unable to achieve success on our first attempt. The first mistake was that of wiring. We failed to realized that there was no clock connected. In other words, the circuit was not receiving any signal. Our next issue was with the chip. The chip had a broken leg, and it just so happened to be a leg which we had a wire pinned to. Our final mistake was with our limit switch. We forgot to tighten down the limit switch, so it was not being fully pressed by the gate until it was very far down. This is the first project this year where we used state machines and VEX components. So I was pretty excited, because I enjoy building and working with the VEX kits. Although there were some differences, the overall process was very similar to previous projects. We were given a task, we translated it into a table, derived the expressions, simulated it in multisim, and breadboarded it. All in all, this project made me realize how much I've learned about circuits, their diagrams, and how to understand what they actually mean. The overall process has become significantly easier when compared to the beginning of the year. The next time I do a project, I will always keep in mind that the project has the sole purpose of furthering my knowledge on the subject.