We can use logic gates to stop car drivers and their passengers forgetting to put their seat belts on. The circuit below will not allow the ignition switch start the car unless the seat belt(s) are fastened. To start the car both the ignition and the seat belt fastened signals must be 1.
If the seat belts are not fastened and the ignition switch is turned, the car will not start and the inputs to the AND gate connected to the buzzer will both be high. The buzzer will sound and alert the driver to fasten the seat belts. The table below shows all the possible signals at each stage.
|
Ignition |
Seat Belt |
Engine (Ignition AND Seat Belt) |
Buzzer Ignition AND NOT Seat Belt) |
|
1 |
1 |
1 |
0 |
|
1 |
0 |
0 |
q |
|
0 |
1 |
0 |
0 |
|
0 |
0 |
0 |
0 |