How to Build a Robot? Part 2: Hardware Selection and Circuit Design

When building a robot, hardware selection is the critical step where the mission definition established during planning is translated into concrete electronic components. In this second part of the series, we look at the core hardware categories needed in a robot project: microcontroller boards, sensors, motors, and the power distribution system.

Choosing a Microcontroller Board

The microcontroller board, which serves as the robot’s “brain,” should be chosen based on the complexity of the project. Boards like the Arduino Uno are sufficient for beginner-level projects that require simple sensor reading and motor control; they’re a popular choice among beginners due to their low cost and broad community support. For projects that need more processing power and wireless connectivity (Wi-Fi, Bluetooth), the ESP32 board may be preferred. For projects requiring camera-based image processing or more complex decision-making algorithms, single-board computers like the Raspberry Pi offer the advantage of running a full operating system. Technical specifications to consider when selecting a board include the number of input/output (I/O) pins, processor speed, memory capacity, and supported communication protocols (I2C, SPI, UART).

Basic Sensor Types and Selection Criteria

Sensor selection depends directly on the robot’s mission definition. For a line-following robot, infrared (IR) sensors provide sufficient data by detecting contrast differences on the floor and are low-cost. For projects requiring obstacle detection, ultrasonic distance sensors (such as the HC-SR04) can detect distances from a few centimeters to a few meters by measuring the sound wave’s echo time. Infrared distance sensors or small-scale LIDAR modules may be preferred for projects requiring more precise navigation. In applications where the robot needs to sense its own orientation and balance, IMU (Inertial Measurement Unit) modules, which combine an accelerometer and gyroscope, are used. When choosing a sensor, the operating voltage, sampling rate, and communication protocol compatible with the microcontroller must always be checked; a mismatched voltage level can damage the sensor or the microcontroller.

Motor and Motor Driver Selection

Motor selection, which drives the robot’s motion, is based on the weight and torque requirements calculated during planning. Brushed DC motors are the most common choice for beginner-level wheeled robots due to their low cost and simple drive circuits. For applications requiring precise angular positioning (such as robot arm joints), servo motors are preferred because their built-in feedback mechanism allows them to hold a specific angle. Motors cannot be connected directly to the microcontroller, because the microcontroller’s pins cannot supply the current a motor draws; for this reason, a motor driver IC such as the L298N or similar is used to control the motor’s direction and speed with low-current signals from the microcontroller. When choosing a motor driver, one with a current capacity equal to or higher than the motor’s rated current should be selected.

Setting Up the Power Distribution Circuit

In a robot project, different components can operate at different voltage levels; for example, motors might be powered at 7.4 volts while the microcontroller runs at 5 volts. Because of this, the power distribution circuit is responsible for converting energy from a single battery source into the voltage level each component needs. This is typically achieved using voltage regulators (such as the 7805 IC) or switching DC-DC converters. Switching converters generate less heat than linear regulators and offer higher energy efficiency, which is why they’re recommended for battery-powered mobile robots. It’s also good engineering practice to keep the motor power line separate from the microcontroller power line (isolated power rails), so that sudden current spikes drawn by the motors don’t affect sensitive electronic components.

Building the Circuit on a Prototype Board

Once the hardware components are decided, it’s recommended to build a prototype on a breadboard before moving to the final circuit board. This stage allows wiring errors to be caught and fixed before any permanent soldering is done. Testing each component individually during the prototype stage — for example, first spinning a single motor through its driver, then checking whether a sensor reads data correctly — makes it easier to pinpoint the source of any errors that arise once the system is integrated.

Common Hardware Mistakes

One mistake beginners often make in hardware selection is trying to connect a motor directly to a microcontroller pin; this usually results in permanent damage to the microcontroller. Another common mistake is wiring sensors without checking their operating voltage; connecting a 5-volt sensor directly to a 3.3-volt microcontroller can cause faulty readings or hardware damage. Additionally, choosing a motor driver with a current capacity below the motor’s actual draw current can cause the driver to overheat and fail.

Conclusion

Hardware selection is the stage where the robot project is physically brought to life, and the technical specifications of every component must be compatible with one another. Correctly matching the microcontroller, sensors, motors, and power distribution system significantly reduces the problems encountered in later stages of the project. In the next part of the series, we’ll cover how to write the software that runs on this hardware and the basic control algorithms involved.

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