1. Overview
This module demonstrates how to implement a steering control system using Pulse Width Modulation (PWM) on NXP S32K3 microcontrollers.
The application reads an analog input from a potentiometer (simulating a steering wheel) and converts it into a servo motor position. As the input changes, the servo motor reacts in real time, mimicking how steering systems work in modern vehicles.
This example is based on Application Code Hub demonstrations for:
In this workshop, a POT Click simulates the steering wheel position. When the student rotates it, an analog voltage proportional to the angle is read by the MCU through the ADC, scaled in software, and converted into a PWM duty cycle. The PWM is generated by the Servo Click (configured by the MCU over I²C) and drives a Micro Servo motor SG 180°, whose angle tracks the potentiometer in real time.
2. Learning Scope
- Understand a basic steering control system and the ideas behind EPS and steer-by-wire.
- Use the POT Click as a simulated steering-wheel input.
- Acquire analog values (0–3.3 V) using the ADC and understand analog-to-digital conversion.
- Perform signal scaling from the ADC range to a servo angle / PWM duty cycle.
- Generate PWM signals to drive a servo motor.
- Configure the Servo Click over I²C using the OE (Output Enable) pin.
- Recognize the actuation data flow: sensor input → MCU processing → PWM actuation.
- Import, build, flash, and debug an ACH project in S32 Design Studio 3.6.5.
- Understand why steering functions are relevant for functional safety.
3. System Architecture
The three elements capture exactly the basic idea of the system in the demo:
- Input: Potentiometer (POT Click simulates the steering-wheel position)
- Processing: S32K3 MCU (reads the ADC, scales the value, commands the actuator)
- Output: Servo motor controlled via PWM (Micro Servo SG 180°)
This matches the classic flow of an embedded actuation system: sensor → processing → actuator.
Functional Flow
The system operates continuously as follows:
- The potentiometer generates an analog voltage based on its position
- The ADC converts this voltage into a digital value
- The application scales this value into a steering angle
- The system generates a PWM signal based on the angle
- The servo motor moves accordingly
This loop runs continuously to ensure real-time control.
Steering Monitoring Application Architecture
4. Key Concepts
4.1 ADC (Analog-to-Digital Converter)
The POT Click outputs 0–3.3 V depending on the wiper position. The ADC samples this voltage at regular intervals and quantizes it into a digital code (a 12-bit ADC produces values between 0 and 4095). The further the potentiometer is turned, the higher (or lower) the digital sample. ADC acquisition is the foundation of automotive sensing — used for torque, throttle, battery voltage, and many others.
4.2 Signal Scaling — From ADC to Servo Angle
The ADC range (for example 0–4095) and the servo range (0°–180°, expressed as a PWM duty cycle) are different. The application performs a linear mapping so that one end of the potentiometer corresponds to one steering extreme and the other end to the opposite. This is the same scaling used in real EPS systems, where a hardware reading is converted into a normalized control command.
4.3 PWM — Pulse-Width Modulation and Servo Control
PWM switches a digital output on and off at a fixed frequency, varying the duty cycle (the fraction of time the signal is high). A hobby servo such as the SG 180° interprets this duty cycle as a position command. In this demo, the PWM is not generated by the MCU itself but by the Servo Click's dedicated PWM controller, which the MCU configures over I²C — a typical embedded pattern that offloads time-critical signal generation and keeps the CPU free for application logic.
4.4 I²C — Configuring the Servo Click
I²C — Inter-Integrated Circuit is a two-wire serial bus made of SDA (data) and SCL (clock). The S32K3 uses LPI2C1 on PTC6 (SDA) and PTC7 (SCL) to configure the Servo Click — PWM frequency, channel, and duty cycle. The OE — Output Enable pin on PTB17 is an additional control line that enables or disables the PWM outputs without reconfiguring the chip, which is also useful for a quick "safe stop" behavior.
4.5 POT Click as Steering Wheel
The POT Click is a simplified, safe stand-in for a real steering sensor. The student rotates it by hand, the voltage changes, the MCU reads it through the ADC, scales it, and the servo reacts.
4.6 Data Flow at a Glance
Physical rotation → analog voltage → ADC sample → scaled command (angle / duty cycle) → I²C configuration of the Servo Click → PWM signal → servo angle. This direct chain from the student's hand to the servo shaft is the main educational value of the demo.
5. Hardware and Software Setup
Required Hardware
| Component | Image | Purpose |
|---|---|---|
| FRDM-A-S32K312 |  |
Alternative MCU platform used to run the steering application and process steering inputs.
|
| FRDM-A-S32K344 |  |
Alternative MCU platform used to run the steering application and control connected peripherals.
|
| FRDM-K64 Click Shield |  |
mikroBUS expansion board used to connect Click modules to the FRDM platform.
|
| Servo Click |  |
PWM driver board used to control the servo motor position.
|
| POT Click |  |
Potentiometer module used to simulate steering wheel input.
|
| Micro Servo SG 180° |  |
Actuator used to convert control signals into steering movement.
|
| USB-C / 12 V supply | — |
Provides power and enables programming and debugging of the system.
|
The example applications demonstrate how these peripherals are connected to the MCU pins and used to simulate steering wheel input and actuator control.
| Steering Control Monitoring on FRDM-A-S32K312 | Steering Control Monitoring on FRDM-A-S32K344 |
|---|---|
 |
 |
Software Environment
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S32 Design Studio IDE
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S32K3 Automotive Software Package
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Application Code Hub project import
6. Implementation Guide
| Step | Action | Sub-steps | Expected Result |
|---|---|---|---|
| 1 | Import the Project |
|
Project successfully appears in workspace |
| 2 | Build the Application |
|
Build completes with no errors and generates .elf file |
| 3 | Connect Hardware |
|
Board is powered and detected by IDE |
| 4 | Flash and Run |
|
Application runs continuously |
| 5 | Functional Validation |
|
Servo follows potentiometer position in real time |
7. Signal Behavior and Control Logic
8. Troubleshooting
| Issue | Possible Actions |
|---|---|
| Board Not Detected |
|
| No Servo Movement |
|
| Incorrect Behavior |
|
| Unstable Movement |
|
9. Extending the Application
The basic implementation can be extended in several ways:
Steering Range Control
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Restrict or extend the actuator's range of motion
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Define software-based limits to protect the mechanics
Input Direction Inversion
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Reverse how the actuator responds to the input
-
Useful for left-hand vs. right-hand drive calibration
Noise Filtering
-
Apply software filtering to stabilize readings
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Avoid jitter near the center position
Scaling Logic Exploration
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Identify and analyze how the input is mapped to the output
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Connect software math with hardware behavior
Fault-Handling Behavior
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Add a mechanism that reacts to a detected fault
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Transition the system into a safer state
State Machine Implementation A more advanced approach is to implement a state machine:
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Idle
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Active
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Fault
10. Safety Context
This example reflects key automotive principles:
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Continuous monitoring of driver input
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Immediate response to control signals
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Reliable actuator control
In real systems:
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Redundancy is required
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Fault detection mechanisms are implemented
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Systems must comply with ISO 26262 (functional safety standard)
Steer-by-wire systems require high reliability since there is no direct mechanical link.
11. Conclusion
This module demonstrates how a simple embedded system can implement steering control using ADC input and PWM output.
It shows how:
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Analog input is acquired
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Data is processed in real time
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Actuators are controlled using PWM
| Result on FRDM-A-S32K312 | Result on FRDM-A-S32K344 |
|---|---|
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 |
The course provides a strong foundation for more advanced systems, including filtering, state machines, and safety-oriented designs.
