Project Title: Simulated Elevator
Description: This is a simplified elevator system implemented using flip-flops. The elevator is designed for a four-story building. It is not able to distinguish between up or down commands. It starts from ground floor and goes to fourth floor and goes down and then up again. If there is a detected call at a particular floor, it stops at that floor for one clock cycle. There are three parts to this circuit. First, one circuit controls the up and down movement of the elevator. Second, one circuit signals passenger call from a particular floor. Third, one circuit displays the current location of the elevator through an 8-segment display.
Circuit 1:� Circuit that controls the up and down movement of the elevator.
A. Function table of the elevator movement
|
PS |
NS |
|
|
u=0 |
u=1 |
|
|
00 |
00 |
01 |
|
01 |
00 |
10 |
|
10 |
01 |
11 |
|
11 |
10 |
11 |
Implemented using D flip-flop:
DA = AB + Bu + Au
DB = BC’ + AC’ + AB
Circuit 2: Circuit that displays the current location of the elevator.
A. Output of D ff decoded using 74139:
|
Input (S0,S1) |
Output |
|||
|
I0 |
I1 |
I2 |
I3 |
|
|
00 |
0 |
1 |
1 |
1 |
|
01 |
1 |
0 |
1 |
1 |
|
10 |
1 |
1 |
0 |
1 |
|
11 |
1 |
1 |
1 |
0 |
B. Output of decoder inputted to 8 line to 3 line priority encoder (74148)
C. Output of encoder is inputted to decoded 7-segment display. This output displays the current location of the elevator.
Circuit 3: Circuit that signals passenger call for elevator and elevator having fetch the passenger.
This circuit introduces a limitation to the system. Ideally, whenever the elevator detects a call, it would stop for one clock cycle at the floor where the call originated, then it would reset the flip-flops corresponding to a particular floor so that the light would go off. However, what the circuit does is that it resets for one clock cycle, then it signal again that there is a call, since the designers were not able to figure out a way to control the switches.
The delay is achieved by the condition that both the Q’ of the flip-flop 5 and the clock edge would both be true.
The elevator is able to detect calls from the different floors (ff 1-4) by activating flip-flip 5 when the inverted output from the encoder and Q of ff 1-4 are both true.
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