Development Plan for Electric Iron Based on FMD MCU

Household electric irons are evolving towards being "lightweight, fast-heating, and intelligent with protection features." Pain points such as slow heating, fabric sticking to the soleplate, and forgetting to turn off the iron during use urgently require a cost-effective "mini brain." The FMD MCU (with an 8-bit 1T core, 12-bit ADC, hardware PWM, operational amplifiers, comparators, and EEPROM) can single-handedly handle temperature control, zero-crossing detection, NTC compensation, touch-sensitive gear selection, and buzzer alerts, transforming the traditional "fast-heating" iron into a "stable-ironing" one.

System Block Diagram

• Main Controller: FMD MCU (SOP16 package, 8 KB Flash / 512 B RAM / 256 B EEPROM)
• Power Supply: AC 220 V → Non-isolated 12 V Buck converter → 5 V LDO → 3.3 V for MCU
• Heating Plate: Aluminum die-cast soleplate + mica heating element, with power options of 1200 W / 1600 W
• Temperature Detection: K-type thermocouple + operational amplifier ×32 → ADC, with a resolution of 0.5 ℃
• Zero-Crossing Detection: AC zero-crossing optocoupler → external interrupt, used for triac phase-shifting triggering
• Touch Slider: 3-channel capacitive touch with built-in MCU touch module for one-finger sliding gear selection/temperature adjustment
• Safety Features: Tilt switch (power off when tilted >45°), fuse, and thermal fuse for dual hardware protection
• User Interface: 3-color LED ring + buzzer (reverse-driven by MCU)

Core Functions

The electric iron MCU solution introduced by FR4PCB.TECH utilizes the FMD MCU as the main controller chip. The functions implemented by the MCU are as follows:

Three-Gear Electronic Temperature Control

• Low Gear (90 ℃): Suitable for silk and wool.
• Medium Gear (140 ℃): Suitable for cotton-linen blends.
• High Gear (190 ℃): Suitable for denim and crease setting.
• The slider allows for real-time fine-tuning by sliding left or right, and the EEPROM remembers the last setting after power-off.

Rapid Heating + Constant Temperature PID Control

• Zero-crossing phase-shifting + PID cycle of 100 ms, heating to 140 ℃ in ≤35 s.
• Temperature fluctuation of ±2 ℃ after reaching the set point, preventing "overheating" and fabric sticking to the soleplate.

Intelligent Dry Burning/Forgetting Protection

• If the NTC detects a temperature rise rate of the soleplate >8 ℃/s, dry burning is determined → the triac is immediately turned off, and the buzzer sounds continuously for 2 s.
• If the iron remains horizontal and stationary for >8 min or is tilted >45° continuously for >30 s, it automatically powers off for cooling, with the LED ring flashing red slowly as a warning.

Steam Pulse Control

• The MCU drives a 5 V diaphragm pump via PWM, with an adjustable pulse cycle of 0.3-1 s and three water volume settings.
• The water pump is linked with the heating PID to ensure instant vaporization without leakage.

Automatic Descaling Reminder

• After accumulating 10 hours of operation, the buzzer sounds and the orange LED flashes, prompting the user to pour in white vinegar for cleaning.
• Descaling procedure: Maintain a constant temperature of 70 ℃ + pulse pump water for 2 min, then heat up to 140 ℃ for 30 s of dry burning for sterilization.

Touch + Buzzer Human-Machine Interaction

• The LED ring follows the slider movement in real-time when sliding and turns off 2 s after releasing, preventing glare at night.
• Different tones accompany button presses, temperature adjustments, completion, and alarms, with a 200 ms buzzer drive by the MCU, eliminating the need for an external IC.

Low Standby Power Consumption

• Power consumption in the off state is <0.3 W, complying with the new EU ERP standby regulations.
• The EEPROM stores user preferences, enabling instant heating upon plugging in without repeated settings.

Development Schedule

• Week 1: Schematic design + 2-layer PCB layout, with copper pouring and windowing in the heating area + differential routing for the thermocouple.
• Week 2: PID parameter tuning to achieve a heating curve of 35 s.
• Week 3: Safety testing for dry burning, tilting, and over-temperature conditions.
• Week 4: Small-batch user testing with 200 units, recording a 90% reduction in the forgetting rate.
• Week 5: Mass production jigs for writing calibration values in 3 s and generating ERP energy efficiency reports with one click.

Conclusion

Using a small 8-bit FMD MCU from Fremont Micro, we have integrated "PID constant temperature control, touch slider, forgetting protection, and automatic descaling" into a compact soleplate: heating in 35 s, constant temperature within ±2 ℃, and automatic power-off after 8 min of inactivity, making every ironing session safe, efficient, and hassle-free.

The above is the electric iron MCU solution shared by FR4PCB.TECH. FR4PCB.TECH provides design and development services for single-chip microcomputer application solutions, offering both 8-bit and 32-bit single-chip microcomputers.