Car Speed Monitor
The speed of an automobile is generally measured by a Hall e¤ect sensor installed near the transmission. The signal provided by this sensor has a frequency fpulse proportional to the car's speed, normally of about 500-2,000 Hz per miles/hour (assume 1 kHz). This exercise concerns the design of a speed monitor, taking fpulse as input, with the following features (a possible view is shown in figure 11.25):
1) Speed selection pushbutton (speed ): Every time it is pressed, the next speed to be monitored is selected, in miles/hour (35 ! 45 ! 55 ! 60 ! 65 ! 70 ! 75 ! 80 ! 35 . . . ).
2) LEDs: Total of eight (one for each speed), with only one lit at a time, indicating the speed being monitored. All LEDs must be turned OFF when the power switch is turned OFF.
3) Numeric display: 3-digit display (LCD or SSD) that shows the car's actual speed (based on fpulse).
4) Buzzer: Must emit a sound when the car approaches the selected speed. Adopt a 2Hz signal when the speed is 3 miles/hour or less from the selected speed, or a continuous signal when at or above the selected speed. Consider that it is a buzzer with internal oscillator, so only a 2Hz square wave is needed in the former case and a continuous DC voltage in the latter.
a) Draw the state transition diagram.
b) Write the VHDL code, then compile and simulate it.
c) Physically implement the circuit in your FPGA board. Use a signal generator or the board's clock to emulate fpulse.