IOT LAB (EC-705) - Important Questions

Interface a temperature/humidity sensor (e.g., DHT11/DHT22) to ESP32, read values, and publish to an MQTT broker; show code flow and explain the MQTT topics and QoS used.

Design and implement PWM control of a DC motor (speed control) using a microcontroller and an H-bridge; include circuit, timing calculations and a test plan.

Create a dashboard in a cloud service (e.g., ThingSpeak/AWS IoT) and demonstrate sending sensor data from a Raspberry Pi; include authentication and sample API calls.

Measure and calculate ADC quantization and error: given a 12-bit ADC and known Vref, compute LSB, expected reading and possible error sources.

Implement low-power sleep/wake strategy for a battery powered sensor node and estimate battery life given active/sleep currents and duty cycle.

Using ESP32, implement MQTT and HTTP client to send sensor data; compare MQTT and HTTP for IoT including QoS, connection overhead and typical use-cases.

Develop a Raspberry Pi project to read a sensor, host a local web dashboard, and demonstrate secure API calls to a cloud service (e.g., ThingSpeak/AWS IoT). Include authentication and secure credential storage.

Design PCB-level interfacing for a 3.3V microcontroller to a 5V sensor: include level shifting, circuit protection (e.g., diodes, series resistors) and isolation techniques; provide circuit diagram and rationale.

Explain TLS-based authentication and secure OTA update process for an IoT device; include certificate usage, mutual authentication and key rotation strategies.

Given a battery powered sensor node with active current $I_{active}$, sleep current $I_{sleep}$, active time $T_{active}$ per cycle, and period $T$, estimate battery life for a battery of capacity $C$ (mAh). Show formulas and compute for $I_{active}=20\,\mathrm{mA}$, $I_{sleep}=50\,\mu\mathrm{A}$, $T_{active}=10\,\mathrm{s}$, $T=3600\,\mathrm{s}$, $C=2000\,\mathrm{mAh}$. Use the average current formula $I_{avg} = \frac{I_{active}\,T_{active} + I_{sleep}\,\left(T - T_{active}\right)}{T}$ and battery life $= \frac{C}{I_{avg}}$ (in hours).

Describe using logic analyzer and oscilloscope to debug an I2C bus showing NACKs: list probe points, expected waveforms, timing measurements to take and steps to isolate the fault.