Viva

Question 1

topic 1: Q2: Why use I2C for sensor communication?

Answer 1

A: I2C allows multiple sensors (e.g. MPU6050, OLED) to share two wires (SDA/SCL), saving GPIO pins and simplifying wiring.

Question 2

topic 1: Q1: What is the function of the ESP32 in the EEEBot?

Answer 2

A: The ESP32 is the central microcontroller. It handles:

Motor control via PWM

Sensor communication (I2C/GPIO)

Wireless communication via Wi-Fi (MQTT in software route)

Question 3

Q3: What happens if I2C pull-up resistors are omitted?

Answer 3

A: The data lines may float, leading to unreliable or failed communication. Pull-ups ensure correct high logic levels.

Question 4

topic 2: Q1: What is the purpose of the MPU6050 in blind maze navigation?

Answer 4

A: The MPU6050 provides gyro and acceleration data. It allows the bot to detect and execute accurate turns (e.g. 90°) without vision.

Question 5

topic 2: Q2: Why are encoders not reliable on their own?

Answer 5

A: Encoders measure wheel rotations but can be affected by slippage or uneven surfaces, leading to cumulative drift over time.

Question 6

topic 2: Q3: What would happen if the ultrasonic sensor was used for all navigation?

Answer 6

A: It would detect obstacles, but cannot provide orientation or direction, making it ineffective for path tracking or turning.

Question 7

topic 3: Q1: How does the EEEBot use the optical sensor array to follow a line?

Answer 7

A: IR sensors detect the contrast between black (absorbs IR) and white (reflects IR). Logic or PID adjusts motor speeds to keep the bot aligned.

Question 8

topic 3: Q2: Why was a pull-down resistor used in the sensor circuit?

Answer 8

A: To ensure a defined low logic level when the sensor output is inactive. Prevents noise or floating voltages on inputs.

Question 9

topic 3: Q3: What happens if the resistor value is too high?

Answer 9

A: The input pin may not pull low fast enough, leading to unstable readings or delayed sensor response.

Question 10

topic 4: Q1: How did the ESP32 integrate with Node-RED for wireless control?

Answer 10

A: Node-RED UI sent commands via MQTT (e.g. “forward”, “left”). The ESP32 subscribed to topics and executed corresponding actions.

Question 11

topic 4: Q2: Why use MQTT instead of HTTP?

Answer 11

A: MQTT is lightweight and uses less bandwidth. It supports real-time, event-based communication—ideal for embedded systems.

Question 12

topic 4: Q3: What happens if the MQTT broker disconnects?

Answer 12

A: The ESP32 won’t receive commands. A failsafe like a timeout or last-will message can be used to stop the bot safely.

Question 13

topic 5: Q1: How were symbols used to control the bot in maze navigation?

Answer 13

A: The Pi camera captured images, and OpenCV recognized shapes (e.g. triangle = forward). The Pi then sent commands over MQTT.

Question 14

Topic 5: Q2: What happens if lighting conditions change?

Answer 14

A: Detection can fail due to poor contrast. Adaptive thresholding or using HSV color filtering can make the system more robust.

Question 15

Topic 5: Q3: How did you ensure the bot moved accurately after a command?

Answer 15

A: The bot used encoders to measure distance and the MPU6050 to ensure accurate rotation angles, maintaining straight and precise motion.

Question 16

Topic 1:What is the purpose of decoupling capacitors on the mainboard?

Answer 16

They filter out voltage spikes and noise on the power supply lines. This protects sensitive components like the ESP32 and ensures stable operation.

Question 17

Topic 1:How do you safely power the ESP32 and other components?

Answer 17

A voltage regulator converts the 7.4V Li-ion battery down to 5V or 3.3V. Care is taken not to exceed the ESP32’s 3.3V logic limits.

Question 18

Topic 1:What are the risks of incorrect pin assignments on the ESP32?

Answer 18

Using wrong pins can damage components or result in communication failure. Some pins are input-only or have special functions (e.g. GPIO34–39 are input-only).

Question 19

Topic 1: How does the ESP32 generate PWM signals for motor control?

Answer 19

It uses dedicated hardware PWM channels (LEDC peripheral) to generate precise signals. These control motor speed via duty cycle modulation.

Question 20

Topic 2: How does the ultrasonic sensor measure distance?

Answer 20

It sends an ultrasonic pulse and measures the time it takes for the echo to return. Distance = (time × speed of sound) / 2.

Question 21

Topic 2: What is dead reckoning and how was it implemented?

Answer 21

It’s a method of estimating current position using previous position and motion data. We used encoders for distance and MPU6050 for rotation to track position blindly.

Question 22

Topic 2: Why might you filter MPU6050 data?

Answer 22

Gyroscopes drift over time and accelerometers are noisy. A complementary filter or Kalman filter fuses data for accurate angle estimation.

Question 23

Topic 2: What are encoder resolution and CPR, and why do they matter?

Answer 23

CPR (counts per revolution) determines movement precision. Higher CPR gives finer control of motion and more accurate distance tracking.

Question 24

Topic 3: Why did you use a sensor array instead of a single sensor?

Answer 24

A single sensor only detects line presence. An array allows directional control—whether the line is to the left, right, or center—enabling steering adjustments.

Question 25

Topic 3: How does a PID controller improve line following?

Answer 25

PID (Proportional-Integral-Derivative) calculates an error value based on sensor input and adjusts motor speeds to reduce that error smoothly and accurately.

Question 26

Topic 3: What are the limitations of IR sensors in line following?

Answer 26

Performance degrades on glossy or dark-colored surfaces. Lighting conditions or line width variations can cause inconsistent readings.

Question 27

Topic 3: Why might analog IR sensors be used instead of digital?

Answer 27

Analog sensors provide a range of values, allowing for finer control with techniques like PID. Digital sensors only give ON/OFF.

Question 28

Topic 4: How did you prevent conflicting MQTT commands?

Answer 28

Commands were serialized, and the ESP32 queued or ignored duplicate/rapid inputs. Delay and control logic ensured commands were executed cleanly.

Question 29

Topic 4: How did you test and debug MQTT communication?

Answer 29

Used the Node-RED debug node and MQTT testing tools like MQTT Explorer to monitor topic traffic and confirm message delivery.

Question 30

Topic 4: What are retained messages and were they used?

Answer 30

Retained messages are stored on the broker and sent to new subscribers. We did not use them, as stale movement commands could be dangerous.

Question 31

Topic 4: How did the ESP32 parse MQTT messages?

Answer 31

The ESP32 used the Arduino MQTT library, parsed incoming strings or JSON payloads, and mapped them to movement functions.

Question 32

Topic 5: How does the image preprocessing work in OpenCV?

Answer 32

Image is converted to grayscale, then thresholded or blurred to reduce noise. Contours are found to detect shape outlines for classification.

Question 33

Topic 5: What methods did you use to classify symbols?

Answer 33

Used contour properties like number of edges (e.g., triangle = 3), Hu Moments for shape comparison, or template matching.

Question 34

Topic 5: How was camera calibration handled?

Answer 34

Ensured the camera was fixed at a consistent height and angle. If more advanced: used OpenCV calibration with a chessboard to correct distortion.

Question 35

Topic 5: What would you do if multiple symbols were detected?

Answer 35

Selected the largest or most central one, assuming it’s closest. If needed, added logic to ignore noisy or partial shapes based on area and aspect ratio.

Question 36

encoder

Answer 36

Encoders can be used to control motor rotation by detecting the motor's rotation angle and speed, this method is called feedback control. This translates mechanical movement into readable data for us to see

Question 37

photodiode

Answer 37

photodiodes convert light into current, otherwise called photocurrent. As the light level increases, so does the current that the photodiode generates, which can be directly and indirectly measured in a circuit.