Warm Reminder: All cases in this article are derived from real projects, involving scenarios such as automotive production lines and smart warehousing. At the end of the article, we provide a Selection Decision Tree and a Beginner’s Pitfall Guide.
1. The Soul-Searching Question for Beginners: What Are the Differences?
Engineer Xiao Wang, who just entered the industry, once asked me: “Master, aren’t PLCs and microcontrollers both control devices? Why do factories use PLCs while I am often looked down upon for using microcontrollers?” This question is akin to asking, “What is the difference between a smartphone and a landline phone?” The key lies in the application scenarios and usage methods.
1.1 Visualizing Basic Concepts
- PLC ≈ Industrial Smartphone: Comes with a shockproof shell (IP67 protection), pre-installed WeChat and Alipay (function block library), and can be used by inserting a SIM card (modular expansion)
- Microcontroller ≈ Circuit Board Building Blocks: Requires soldering a screen and installing a battery (building peripheral circuits), manually coding to develop apps (writing low-level drivers)
For example: To make the workshop conveyor belt start and stop automatically
- PLC Solution: Buy a ready-made controller → Drag and drop ladder diagrams → Connect to sensors → Start production the same day
- Microcontroller Solution: Design the circuit board → Write C language code → Debug communication protocols → Still fixing bugs three months later
2. Hardware Section: From “Steel Straight Man” to “Delicate Boy”
2.1 Hardware Architecture Comparison
| Feature | PLC | Microcontroller |
|---|---|---|
| Anti-Interference Capability | Can withstand 2000V surges (can endure interference from welding machines) | May crash when encountering a drill |
| Expansion Capability | Plug-and-play modules (like USB hard drives) | Requires redrawing the PCB (comparable to organ transplantation) |
| Maintenance Difficulty | Hot-swappable replacement (like changing a light bulb) | Requires soldering iron and oscilloscope (surgical level) |
Bitter Lesson: In 2019, during a DCS system upgrade at a chemical plant, an engineer mistakenly installed the microcontroller temperature control board near the reactor, causing temperature data drift due to electromagnetic interference, nearly leading to an accident.
3. Programming Section: The “Love-Hate Relationship” Between Ladder Diagrams and C Language
3.1 Two Implementations for Controlling Motor Direction
PLC Ladder Diagram:
|--[ ]X0------[ ]X1-----------------(Y0)--|
| | | | |
| |--[ ]X1-| | |
| |--[ ]X0------(Y1)-----| |
(Like building blocks: X0=forward button, X1=reverse button, Y0/Y1=output relays)
Microcontroller C Code:
while(1){
if(KEY1) {
GPIO_SetBits(MOTOR_FW); // Set forward pin high
GPIO_ResetBits(MOTOR_BW);// Set reverse pin low
}
else if(KEY2){
GPIO_ResetBits(MOTOR_FW);
GPIO_SetBits(MOTOR_BW);
}
}
(Requires manual handling of interlock logic; beginners often forget to add debounce delays)
3.2 Programming Differences in Real Projects
| Scenario | PLC Advantages | Microcontroller Advantages |
|---|---|---|
| Elevator Floor Control | Comes with a built-in floor register, direct assignment | Requires arrays for state memory |
| PID Temperature Control | Calls existing PID function blocks | Must manually write differential equations |
| Ethernet Communication | Just configure parameters (like filling out a web form) | Must port the LWIP protocol stack |
4. Selection Guide: 8 Key Decision Factors
Based on 24 real projects, here is the Selection Decision Tree:
- Harsh Environment: If there is oil or vibration, choose PLC (automotive production line)
- Development Cycle: If less than 2 weeks, choose PLC (urgent modification project for a mask machine)
- Expansion Needs: If adding vision/robotics, choose PLC (lithium battery assembly line)
- Cost Sensitivity: For mass production > 1000 units, consider microcontroller (smart lock project)
- Technical Reserve: If the team has electronic engineers, use microcontroller (medical device development)
- Communication Complexity: If industrial protocols like PROFINET are needed, choose PLC (tobacco logistics system)
- Maintenance Convenience: If users are not technically savvy, choose PLC (rural sewage treatment station)
- Real-Time Requirements: For μs-level response, use microcontroller (laser cutting control)
5. Hard-Earned Experience: Pitfalls I’ve Encountered Over the Years
5.1 Case Studies of Selection Errors
- Case 19: Designed a dust removal system for a steel plant, used STM32+RS485 to save costs, but the RS485 chip was damaged by welding interference, ultimately switching to PLC to recover losses
- Case 23: Insisted on using PLC for a smart agricultural greenhouse, but lost the bid due to high costs; switched to ESP32 solution and won the bid
5.2 Safety Precautions
- PLC cabinets must be grounded (previously burned CPU modules due to poor grounding)
- Microcontroller boards should have TVS diodes (saved 0.5 yuan on protective components, incurred 20,000 yuan in repair costs)
- Essential for on-site debugging:
- PLC Engineer: Insulated gloves + multimeter
- Microcontroller Engineer: Anti-static wrist strap + logic analyzer
6. Advanced Path: From Beginner to Expert
6.1 Suggested Learning Path
| Stage | PLC Learning Focus | Microcontroller Learning Focus |
|---|---|---|
| Beginner | Basics of Ladder Diagrams/Wiring Standards | GPIO Control of LED |
| Bronze Level | Using Function Blocks/Analog Processing | Interrupts and Timers |
| Silver Level | Motion Control/PROFINET Communication | Porting FreeRTOS |
| Gold Level | Redundant Systems/SCADA Integration | Embedded Linux Development |
6.2 Recommended Tool List
-
PLC:
- Multimeter (Uni-T UT89X)
- Simulation Software (CODESYS)
- Label Printer (Brother PT-E550W)
-
Microcontroller:
- Oscilloscope (Pico DS1054Z)
- Logic Analyzer (DSLogic)
- Debugging Tool (J-Link V11)
7. Practical Training: From “Hello World” to Industrial Applications
7.1 Basic Exercises
- PLC Version: Use a timer to implement the “Turn on Light for 5 Seconds → Sound Buzzer for 3 Seconds → Turn off Light” loop
- Microcontroller Version: Use PWM to achieve breathing light effect (pay attention to dead time settings)
7.2 Comprehensive Projects
-
Beginner Level: PLC—Automated Parking Garage Vehicle Counter Microcontroller—Smart Pot Moisture Control
-
Advanced Level: PLC—Packaging Machine Synchronous Control System Microcontroller—Elevator Call Panel Based on CAN Bus
Next Issue Preview: “Step-by-Step Guide to Upgrading Arduino Projects to Industrial-Grade PLC Systems—Taking Smart Warehouse Vehicle Transformation as an Example”Bonus Material: Follow our public account and reply “PLC Combat Table” to obtain the complete document package of 24 cases