An Embedded Engineer at Plexus plays a critical role in the product realization lifecycle, transforming complex concepts into fully functional, high-reliability physical products. As a global leader in design, manufacturing, and aftermarket services, Plexus partners with companies in highly regulated industries, including healthcare and life sciences, aerospace and defense, industrial, and semiconductor capital equipment. In this role, you are not just writing isolated code; you are building the software foundation for devices where failure is not an option, such as medical ventilators, flight control systems, and advanced industrial automation tools.

Working as an Embedded Engineer here means collaborating closely with cross-functional teams of hardware designers, mechanical engineers, and manufacturing specialists. You will be responsible for bridging the gap between hardware and software, writing firmware that interacts directly with custom microcontrollers, sensors, and actuators. The sheer variety of projects ensures that you will constantly face new technical challenges, requiring you to adapt to different microprocessors, real-time operating systems (RTOS), and communication protocols.

This position is ideal for engineers who thrive on technical diversity and take pride in seeing their code drive physical hardware. Because Plexus works with external clients to bring their products to life, your work will have a direct, tangible impact on market-leading technologies worldwide. To succeed, you must combine deep technical expertise in low-level programming with strong communication skills to navigate client requirements and collaborative engineering environments.

The questions you will encounter during the Plexus interview process are designed to evaluate your practical engineering skills, your understanding of low-level software design, and your ability to talk confidently about your past work. The following questions are representative of what candidates face, drawn from real interview experiences.

Embedded C/C++ Programming

These questions assess your understanding of memory management, hardware-level programming, and the nuances of the C and C++ languages in resource-constrained environments.

• What is the purpose of the volatile keyword in C, and in what scenarios must an embedded engineer use it?
• Explain the difference between static variables inside a function versus static variables defined globally.

Preparing for an interview at Plexus requires a balanced approach of reviewing core computer engineering concepts and thoroughly reviewing your own portfolio. The interviewers want to see that you are both a capable coder and a practical hardware debugger.

Embedded C/C++ Mastery – You must have a flawless understanding of low-level C programming. This includes pointer arithmetic, bitwise operations, memory mapping, and optimization techniques. Expect to write code or explain code snippets during your technical rounds.

Modular System Design – You should practice breaking down everyday physical systems (like a vending machine, microwave, or traffic light) into clean, modular firmware architectures. Focus on defining clear interfaces between software modules and the hardware abstraction layer (HAL).

Resume and Project Integrity – Be ready to defend every single line on your resume. If you list a project, you must be able to explain the schematic, the microcontroller used, the firmware architecture, and the specific debugging challenges you faced.

Engineering Fundamentals – Review basic circuit theory, digital logic, and communication protocols. You should know how SPI, I2C, and UART work at both a physical and logical level, including signal lines, clocking, and addressing.

The interview process for the Embedded Engineer role at Plexus is structured to evaluate your technical competency, academic background, and practical design capabilities. It typically begins with an initial touchpoint, such as a campus recruiting event or a LinkedIn application. If you apply online, you will often start by filling out a detailed skill-set competency form. This form asks you to self-rate your experience with various microcontrollers, tools, operating systems, and programming languages, which the hiring team uses to determine how to route your application.

Once selected to move forward, you will undergo an initial screening phase. This usually consists of a 30-to-45-minute phone or on-campus interview. This conversation is highly conversational and focuses on your background, your engineering interests, and basic technical concepts. Be prepared for a close look at your academic record during this stage; if you have a lower GPA, recruiters will ask you to defend it and explain how your practical project experience compensates for it.

The final and most critical stage is a deep-dive technical interview, typically conducted over a video call with a functional manager or a panel of senior engineers. This interview lasts approximately 1.5 hours and is heavily focused on embedded C programming, debugging methodologies, and system design. You will be asked to walk through your resume projects in detail and solve a comprehensive design scenario on the spot.

This visual timeline illustrates the typical progression from your initial contact to the final decision. Candidates should use this timeline to pace their preparation, ensuring they complete their core C/C++ review prior to the intensive final technical call.

To succeed at Plexus, you need to perform exceptionally well across three core evaluation areas during your technical interviews.

Embedded C/C++ Proficiency

Your ability to write clean, efficient, and hardware-aware code is the foundation of the evaluation. Plexus engineers write firmware for systems with limited memory and processing power, making code efficiency and safety paramount.

Be ready to go over:

• Pointer Manipulation – Understanding pointer arithmetic, casting pointers to hardware addresses, and function pointers.
• Bitwise Operations – Masking, setting, clearing, and toggling specific bits in registers.
• Memory Management – The differences between stack, heap, and static memory, and why dynamic allocation is avoided in high-reliability systems.
• Advanced concepts (less common) – Writing reentrant functions, managing race conditions in multi-threaded RTOS environments, and implementing lock-free queues.

Example questions or scenarios:

• "Write a C function to reverse the bits of an 8-bit unsigned integer."
• "Explain how you would write a safe Interrupt Service Routine (ISR) that communicates with a background task."

Embedded System Design

Interviewers want to see how you approach designing a complete embedded product from scratch. This tests your ability to bridge the gap between high-level requirements and low-level implementation.

Be ready to go over:

• State Machine Design – Structuring firmware using finite state machines (FSM) to handle complex system behaviors.
• Hardware Abstraction Layers (HAL) – Separating hardware-dependent code from application logic to ensure portability.
• Driver Development – Designing drivers for common peripherals (ADC, DAC, PWM) and communication buses (SPI, I2C).
• Advanced concepts (less common) – Designing low-power sleep state transitions and implementing watchdog timers for system recovery.

Example questions or scenarios:

• "Walk me through the software modules, tasks, and state transitions you would design for a smart vending machine."
• "How would you design a system to reliably log sensor data to an external flash memory over SPI while handling sudden power failures?"

Project Architecture & Code Integrity

This area evaluates your practical engineering experience and honesty. The panel will drill down into your past projects to see if you truly understand the design decisions made.

Be ready to go over:

• Schematic Reading – Your comfort level looking at a hardware schematic to write corresponding firmware.
• Debugging Methodologies – Using oscilloscopes, logic analyzers, and JTAG debuggers to isolate issues.
• Protocol Selection – Explaining why you chose a specific communication interface over another in your projects.

Example questions or scenarios:

• "On the microcontroller project listed on your resume, explain why you chose SPI instead of I2C for your display interface."
• "Describe a scenario where your microcontroller was hanging, and walk me through the exact steps you took to find the root cause."