🌡️ STM8 Temperature Controller

A temperature controller based on STM8S105K4 — reads temperature via NTC thermistor, controls Heater/Cooler relays, displays on 4-digit 7-segment LED, and communicates with PLC via Modbus RTU/ASCII.

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📦 Key Features

Feature	Description
Temperature measurement	NTC thermistor via 10-bit ADC, Steinhart-Hart equation
Temperature control	Heater / Cooler relays with hysteresis (delta)
Display	4-digit 7-segment LED (multiplexed)
PLC Communication	Modbus RTU / ASCII over UART2 (9600 baud)
Persistent config	Internal EEPROM (1 KB)
NTC calibration	Recalibrate coefficients A, B, C based on reference temperature

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🧩 Software Architecture

┌─────────────────────────────────────────────────┐
│                    main.c                        │
│  ┌──────────┐ ┌──────────┐ ┌──────────────────┐ │
│  │  ADC/NTC │ │ 7-Seg UI │ │ Button Handler   │ │
│  │ measure  │ │ display  │ │ BT1: Power/Reset │ │
│  │ & calc°C │ │ temp     │ │ BT2: Setting     │ │
│  └──────────┘ └──────────┘ │ BT3: Up   (▲)    │ │
│  ┌──────────┐ ┌──────────┐ │ BT4: Down (▼)    │ │
│  │  EEPROM  │ │ Timers   │ └──────────────────┘ │
│  │ save/load│ │ T1: LED  │                      │
│  │ config   │ │ T2: Debounce                     │
│  └──────────┘ │ T3: 1s   │ ┌──────────────────┐ │
│               │ T4: Modbus│ │   modbus.c       │ │
│               └──────────┘ │ RTU: 03/06/10    │ │
│                            │ ASCII: 03/10     │ │
│                            │ CRC16 / LRC      │ │
│                            └──────────────────┘ │
└─────────────────────────────────────────────────┘

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⚙️ MCU Specs — STM8S105K4

Spec	Value
Clock	8 MHz (HSE external)
Flash	16 KB
RAM	2 KB
ADC	10-bit, 9 channels
EEPROM	1 KB
Interfaces	UART, I²C, SPI
Voltage	2.95 – 5.5 V

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🔌 Pin Map

Pin         Function            Pin         Function
────────────────────────      ────────────────────────
PA1         OSC IN             PC1         LED digit 4
PA2         OSC OUT            PC2         Seg G
PB0         Button 1 (Power)   PC3         Seg C
PB1         Button 2 (Setting) PC4         Seg DP
PB2         Button 3 (Up ▲)    PC5         Seg D
PB3         Button 4 (Down ▼)  PC6         Seg E
PB4         ADC IN4 (NTC)      PC7         Seg B
PB5         Relay Heat         PD0         LED digit 3
PD1         SWIM (Debug)       PD2         LED digit 2
PD5         UART2 TX           PD3         Seg F
PD6         UART2 RX           PD4         Seg A
PF4         Relay Cool         PD7         LED digit 1

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🎮 Button Guide

Button	Short Press	Long Press
BT1 (Power)	Exit setting / Reset show mode	Toggle display on/off (sleep)
BT2 (Setting)	Enter setting mode	Hold BT2 + ▲/▼ = select Fn → release = edit Fn
BT3 (▲)	Increase value / Switch mode	—
BT4 (▼)	Decrease value / Switch mode	—

Factory reset: Long press BT1 → reset all defaults (T=20°C, delta=3, addr=1, sample=3)

Display Mode (show_mode)

Mode	Display	Note
0	Current temperature (°C)	Default
1	Modbus slave address	Prefix A
2	Delta (hysteresis)	Prefix d

Setting Mode (setting_mode)

Mode	Setting	Prefix
1	Modbus slave address (1–99)	A
2	Delta / hysteresis (0–99)	d
3	Target temperature (setting_T)	—
4	Sample time in minutes (1–99)	S
5	Buffer_T — calibration offset	—

Auto-exits setting after 15 seconds of inactivity.

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📡 Modbus (PLC Communication)

• Baud: 9600, 8N1
• Used to communicate with PLC

Code	Function	Description
0x03	Read Holding Registers	Read data from EEPROM
0x06	Write Single Register	Write 1 register to EEPROM
0x10	Write Multiple Registers	Write multiple registers to EEPROM

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💾 EEPROM Map

Address	Size	Content
0x00	1 byte	Modbus slave address
0x01	1 byte	Delta (hysteresis)
0x02–0x05	4 bytes	Setting temperature (float)
0x06	1 byte	Relay heat state
0x07	1 byte	Relay cool state
0x08	1 byte	Sample time (minutes)
0x09–0x0C	4 bytes	Buffer temperature (float)
0x0D–0x2D	4×7 bytes	NTC coefficients: A, B, C, L1, L2, L3, Y1, Y2, Y3

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📁 File Structure

STM8/
├── main.c      # Main program: ADC, LED, buttons, timers, EEPROM, NTC
├── main.h      # MCU declarations, pin map, constants, prototypes
├── modbus.c    # Modbus RTU/ASCII handler, CRC16, LRC
└── modbus.h    # Function code definitions, Modbus prototypes