Toll Booth
Description
We got the expressions for each input of the flip flops by using the inputs, limit open/close and switches open/close, and the Qa and Qb, the outputs of the flip flops, to create unsimplified expression. Once we got the expression we used boolean algebra to simplify the expression as much as possible. Those expressions utilized the Qa and Qb as well as the other inputs, limits and switches, even in final. The outputs, motor open/close and gate open/close, were found by using the same method of tracing the transition table to find unsimplfied expressions then boolean to simplify. But with these expressions the inputs that were limit and switches were eliminated so they only consisted of variations with Qa and Qb. There were 4 states in this state machine so only 2 variables were needed to show the four different states, Qa and Qb. These were shown by state zero being Qa-0 Qb-0, state one Qa-0 Qb-1 and so on like a truth table for 4 states.
Our circuit started with the gate closed or state 0 with the closed LED on. To proceed to the next state we then pressed the first button on the PLD chip to make the gate open. The gate then stopped once it hit the top limit switch and the open LED came on. Then we pressed the second button on the PLD chip to close the gate and it stopped when it reached the second limit switch turning the closed LED back on.
Our circuit started with the gate closed or state 0 with the closed LED on. To proceed to the next state we then pressed the first button on the PLD chip to make the gate open. The gate then stopped once it hit the top limit switch and the open LED came on. Then we pressed the second button on the PLD chip to close the gate and it stopped when it reached the second limit switch turning the closed LED back on.
Conclusion
We started this project by first trying to understand the scenario, since it was a little difficult to understand at first. Once we understood we proceeded to the state graph which you assisted us with and from that we were able to complete our transition table for the toll booth. From the transition table we created the unsimplified expressions for each of the inputs to the flip flops and each of the outputs. With the unsimplified expressions we used booloean algebra to simplify each one as much as possible. After we found the simplified expressions we created the multisim and at the same time followed the schematic to create the breadboard and the toll booth machine. Once we completed and tested the multisim we uploaded it to the completed breadboard and toll booth. But, the first time we tested it it did not work, so we had to find the problem. The problem ended up being a misplaced wire then when moved to the right place made the toll booth work correctly. The only other problem we encountered was two lines were messed up on the transition table so we ended up having to change Qa* for the first flop flop. Major components we used in our design was a bus, a 4 state state machine, motor driver, and button and LED input/outputs. This project was similar to the previous state machine projects in how we did the multisim but different because we uploaded it and also utilized a bus. When reading schematics we learned that you have to go slow and make sure to use the correct components. It has become easier since the beginning of the school year to read schematics since we have had much more practice. Next time I would just try and make sure every step is right so that if there is a mistake it isn't like this time where multiple things had to change from one small mistake.