As an integrated platform combining sensing, control, driving and power management, the intelligent car serves as an effective carrier for learning and practicing electronic system design. Its design involves multiple core links such as sensor signal conditioning, motor driving, embedded algorithms and power conversion. Based on classic design cases, this paper systematically analyzes the key points of component selection for each link and discusses how to improve the reliability, accuracy and energy efficiency of the system by selecting devices with better performance parameters.

System Architecture and Sensor Selection Analysis

A typical intelligent car system usually consists of three layers: perception, control and execution.

• Perception Layer: Responsible for acquiring environmental information such as path, obstacles and light source position.
• Control Layer: With a microcontroller as the core, it processes sensor data and executes control algorithms.
• Execution Layer: Mainly refers to the motor drive circuit, which is responsible for controlling the movement of the car.

In sensor selection, focus should be placed on its output characteristics (analog/switching quantity), detection range, response speed and environmental anti-interference capability. For example:

• Path Detection: Infrared reflective sensors are commonly used. The core lies in the matching of the transmitting tube and receiving tube, as well as the stability of the threshold setting of the subsequent comparator circuit. Changes in ambient light may interfere with the received signal, so it is necessary to select receiving devices with strong anti-interference ability and optimize the optical structure.
• Obstacle Detection: Infrared or ultrasonic ranging modules are adopted, which should be selected according to the requirements of detection distance, accuracy and response time.
• Light Source Detection: Photoresistors or photodiodes are used. The response nonlinearity of photoresistors, as well as the sensitivity and spectral response range of photodiodes, are key factors to be considered.

Design of Motor Drive Circuit and MOSFET Selection

H-bridge circuits are usually used for the driving of DC motors to realize forward and reverse rotation and PWM speed regulation. The key to the design lies in the selection of power switching devices.

1. Challenges of Drive Circuits

• Transient voltage stress: Motors are inductive loads. When PWM is turned off or commutation is performed, the sudden change of inductor current will generate back electromotive force, which may form voltage spikes between the drain and source of the switching tube.
• Conduction loss: Under PWM modulation, the switching tube is in the on state for a long time, and its on-resistance Rds(on) directly determines the magnitude of this part of the loss.
• Thermal management: The switching tube and motor will generate heat during frequent start-stop, locked-rotor or high-speed operation, so it is necessary to ensure that the device junction temperature is within the safe range.

2. Key Parameter Considerations for MOSFETs

To address the above challenges, the selection of MOSFETs for driving should focus on voltage withstand Vds, on-resistance, gate charge and body diode characteristics. For example, for the driving of small DC motors (operating voltage < 12V, continuous current < 5A), MOSFETs with a voltage withstand of more than 30V and an Rds(on) of tens of milliohms can be selected. Hekotai Electronics provides medium and low voltage MOSFETs such as the HKTD series, whose parameters such as Rds(on) as low as 20mΩ help optimize driving efficiency.

Resistor Selection in Sampling and Signal Conditioning Circuits

In circuits such as current sampling, sensor voltage division, and signal pull-up/pull-down, the precision and stability of resistors directly affect the system performance.

1. Analysis of Key Application Points

• Current sampling resistors: Connected in series in the motor circuit or power path for overcurrent protection or current loop control, requiring precise resistance value, low temperature coefficient and sufficient power margin.
• Precision voltage division resistors: Used to convert the resistance change of sensors (such as photoresistors) into voltage signals collectible by the MCU. The stability of the voltage division ratio of the resistor pair determines the measurement accuracy.
• Pull-up/pull-down resistors: Ensure that the digital IO port is in a definite state, and the resistance value selection needs to balance power consumption and switching speed.

2. Technical Advantages of Alloy Resistors

Alloy resistors have more advantages than ordinary thick film resistors in occasions requiring high precision and stability:

• Low temperature coefficient: The TCR of high-quality alloy resistors can be as low as ±50ppm/℃ or even better, which can maintain stable resistance value in a wide temperature range and reduce measurement errors caused by changes in ambient temperature.
• Good long-term stability: When working under rated power and temperature, the resistance value has little drift over time.
• High power density and pulse bearing capacity: Suitable for sampling occasions where instantaneous large current may exist.

The automotive-grade alloy resistor products provided by Hekotai have excellent performance in parameters such as TCR and long-term stability, and are suitable for learning or advanced projects with high reliability requirements.

Conclusion

Component selection for intelligent cars is a systematic trade-off process. In the motor drive part, MOSFETs with appropriate voltage withstand, current capacity, on-resistance and switching characteristics should be selected according to the motor electrical parameters and drive topology, and voltage spikes and heat dissipation issues should be properly handled. In the sensing and signal chain part, components such as resistors with temperature coefficient and long-term stability meeting expectations should be selected according to the measurement accuracy requirements. By deeply understanding the key parameters of each device and their impact on system performance, and referring to the specification data provided by reliable suppliers such as Hekotai, designers can build a more stable, efficient and reliable intelligent car system.