Assignment

Unlike lab projects, all HW assignments should be done individually. Discussion with friends should be limited to clarification of problems and approaches. Sharing or copying of the solutions will be treated as academic dishonesty.

An ultrasonic range sensor can be mounted on a TI MSP432 board (which is mounted on a mobile robot) so as to determine the distance between the sensor/board/robot and an obstacle. You are to design an obstacle warning system so that LED on p1.0 works as follows. LED is off when the one-way distance (not round-trip) is more than three feet. It flashes at one Hz (i.e., 0.5 seconds on and 0.5 seconds off) between one and three feet. And it stays on when the distance is less than one foot. You should submit the following results.

(1) Draw a (very) simple diagram to illustrate the pin connection between the sensor and the MSP board. You need to specify the TI MSP port pins used (except VCC and GND). If a pin is not used as a general purpose I/O pin, its label should clearly identify its usage (e.g., pins used for timer/SCI/SPI.)

(2) Draw three timing diagrams, one for each of three different cases (i.e., LED off, one Hz, and on). Each diagram should contain the Trig, SensorSig, and LED waveforms with the timing quantitatively specified.

(3) Draw a high-level flow chart which should work even when no obstacle is in front of the robot.

• For flow chart notations, follow the convention in https://en.wikipedia.org/wiki/Flowchart and use dashed lines for ISRs. Note that only one outgoing edge is allowed from each "process" box (i.e., rectangle).

• The control flow, the triggering timing (i.e., how to achieve four-time-a-second triggering), and how the LED is flashed (i.e., how to achieve one Hz flashing) should be made clear in the chart.

• As to the level of details in the chart, you may use terms such as "initialization", "measure pulse width", "delay 4 msec", "set pin x.y", "enable XYZ interrupt" (XYZ: the type of interrupt), and so on.

Use all of the following assumptions.

• The speed of sound is 1,000 feet/sec.

• The sensor has the following four pins: Trig, SensorSig, VCC (+3.3V), and GND. Both Trig and SensorSig are digital signals of 0/3.3 volt values. A rising edge on the Trig pin starts the sensor which will trigger the sending out of an ultrasound at a later time, indicated by a rising edge on the SensorSig pin. When the sound returns to the sensor, there is a falling edge on the SensorSig pin. It takes a non-deterministic amount of time (between 0.01 sec and 0.03 sec) for the sensor to send out an ultrasound after receiving the Trig rising edge. The pulse on the Trig pin should last at least 10 micro-seconds. A new pulse on the Trig pin starts the process again, even if the previous ultrasound has not been echoed back.

• The sensor is to be started (or triggered) four times every second.