Rays Power Infra Embedded Systems Engineer Interview: Rounds, Questions and Preparation

What the job involves

An Embedded Systems Engineer in EV and cleantech works on the low-level software that controls battery management systems, motor controllers, chargers, and energy monitoring units. Day to day you write and debug firmware in C on microcontrollers, interface with sensors and power electronics over CAN, SPI, and I2C, and test the system on benches and in vehicles or solar installations. You often work closely with hardware, testing, and field teams to ensure safe, efficient, and reliable operation.

Role and Technical Knowledge

1. 1

   Explain the difference between a microcontroller and a microprocessor, and why microcontrollers are preferred in EV battery management systems.

   Cover integration of peripherals, low power, real-time determinism, and cost. Mention that BMS needs multiple ADCs, CAN, and timers on a single chip.

2. 2

   What is the role of a CAN bus in an electric vehicle, and how does it differ from UART or SPI?

   Highlight multi-master, differential signaling, error detection, and robustness in noisy automotive environments. Compare with point-to-point and shorter-distance protocols.

3. 3

   Describe how you would interface a temperature sensor (like NTC thermistor) to an ADC and convert the reading to degrees Celsius in firmware.

   Mention voltage divider, ADC resolution, reference voltage, Steinhart-Hart or lookup table, and filtering. Show awareness of self-heating and calibration.

4. 4

   What are the key considerations when writing firmware for a Battery Management System to ensure safety and accuracy?

   Talk about cell voltage monitoring, overcurrent protection, state of charge estimation, watchdog timers, redundancy, and compliance with safety standards.

Practical Scenarios and Problem Solving

1. 5

   Your firmware on a motor controller occasionally resets when the motor starts. How would you debug this?

   Check power supply droop, decoupling capacitors, ground loops, and brown-out detection. Use oscilloscope to monitor Vcc and reset pin during startup.

2. 6

   You need to implement a state machine for a charging station that handles idle, charging, fault, and full states. How would you structure it in C?

   Use enum for states, switch-case with function pointers or table-driven approach, and ensure non-blocking transitions. Mention handling of events and timeouts.

3. 7

   How would you test a BMS firmware before deploying it in a vehicle?

   Describe unit tests on host, hardware-in-the-loop simulation, cell simulator, fault injection, and gradual integration from bench to vehicle.

4. 8

   A solar inverter's embedded system needs to log energy data every minute. How would you store data reliably in case of power loss?

   Use non-volatile memory like EEPROM or flash with wear leveling, write-ahead logging, and checksums. Mention periodic flush and power-fail interrupt handling.

Behavioural and Teamwork

1. 9

   Tell me about a time you had to learn a new microcontroller or tool quickly for a project.

   Use STAR method: describe the situation, the specific tool (e.g., STM32CubeIDE), how you learned it, and the outcome. Show self-driven learning.

2. 10

   Describe a situation where you found a bug that others had missed. How did you handle it?

   Focus on systematic debugging, communication with team, and preventing recurrence. Emphasize documentation and root cause analysis.

3. 11

   How do you prioritize tasks when you have multiple deadlines, such as firmware updates for both a charger and a motor controller?

   Talk about impact assessment, communication with stakeholders, using tools like Kanban or simple lists, and delivering critical fixes first.

4. 12

   Give an example of a time you worked in a team to complete a hardware-software integration project.

   Highlight collaboration with hardware engineers, clear interface definitions, regular sync-ups, and joint debugging sessions.

HR and Company Fit

1. 13

   Why do you want to work in the EV and cleantech sector, and specifically in embedded systems?

   Connect personal interest in sustainability with technical passion for embedded control. Mention desire to work on impactful technology.

2. 14

   Are you willing to relocate to a project site or manufacturing facility if required?

   Be honest but show flexibility. If yes, explain willingness to gain hands-on experience. If no, suggest alternative ways to contribute.

3. 15

   Where do you see yourself in three years in this role?

   Show ambition to grow into senior embedded engineer or technical lead, with deeper expertise in EV powertrain or energy systems.

4. 16

   What do you know about our company's work in renewable energy and how does this role contribute?

   Research the company's projects (e.g., solar parks, EV charging) and link embedded systems to reliability and efficiency of their products.