Input: The input variables are OS (Open Switch) CS (Close switch) OL (Open Limit) and CL (Close limit). These inputs determine what the machine should do in relation to the activated inputs.
Outputs: The outputs are open motor, close motor, open gate and closed gate. These outputs are determined by the current state of the inputs, (OS CS OL CL). When open motor is activated that means that the motor is raising the gate. When close motor is activated that means that the motor is lowering the gate. Open gate means that the upper limit switch has been triggered and the gate is fully open while closed gate means that the lower limit switch has been triggered and the gate is closed.
States: There are 4 states; s0,s1,s2 and s3 and each are represented by a binary equivalent.
When the gate is closed, open switch is triggered so the gate will rise until the upper limit switch is hit (OL). From there the operator would press close switch so the motor would lower the gate until the lower limit switch is triggered (CL). From there the process can be repeated.
Conclusion
My design process consisted of following the directions given to us in the packet. The biggest mistake we had was trying to figure how to correctly wire the IC that controlled the motor. The main components used were the 74LS74 Flip Flop and PLD chip. This project was similar to others in terms of wiring, but different as it had a real world application. It connected to a working tollbooth arm and Limit switches. This took quite a lot of thought to manage to create the PLD circuit and to translate the state table into a working project. If I were to redo this project I would change the pins on the PLD to make it easier for bread boarding.