☕ Coffee Roaster Controller

Recipe-driven coffee roasting system with closed-loop temperature control and automated fan management — built on STM32F4.

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📚 Table of Contents

• Features
• System Overview
• System Architecture
• Picture Demo
• Board Information
• Pin Mapping
• Recipe Profile
• Temperature Decode
• Fan Control
• Getting Started
• Toolchain Setup
• Known Issues / Future Work

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✨ Features

• Closed-loop temperature control via Modbus RTU to an external PID controller
• 18-step roast profile — each step defines target temperature and hold time
• Automated PWM fan control across all system states (STANDBY → WARMUP → ROASTING → COOLING → COMPLETE)
• Thermal fail-safe — fan stays on at 70% in FAULT state
• RS-485 / MAX485 communication with no external Modbus libraries
• UART debug output at 115200 baud via ST-Link Virtual COM Port

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🧭 System Overview

The STM32 communicates with an external PID temperature controller over Modbus RTU (RS-485 / MAX485). An 18-step roast profile is stored on-device — each step defines a target temperature and hold time. The system automatically advances through steps when both time and temperature conditions are met, controls a PWM fan across all states, and defaults to fan-on in FAULT for thermal safety.

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🏗️ System Architecture

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🎬 Picture Demo

   

Left: Roasted beans  |  Center: Controls  |  Right: Heating pre-test with PID controller

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🧭 Board Information

Property	Value
Board	NUCLEO-F4xx
MCU	STM32F4xx, ARM Cortex-M4
Clock	84 MHz (HSI PLL)
Flash / RAM	512 KB Flash / 128 KB RAM
Power Source	USB 5V → onboard 3.3V regulator
Logic Voltage	3.3V

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🔌 Pin Mapping

Peripheral	MCU Pin	Function / Connection	Notes
USART1 TX	PA9	Modbus RTU TX → MAX485	9600 baud, 8N1
USART1 RX	PA10	Modbus RTU RX ← MAX485	Reads tempPV from PID
USART2 TX	PA2	Debug UART TX	115200 baud
USART2 RX	PA3	Debug UART RX
TIM3 CH1	PA6	PWM fan output	0–999 CCR1 = 0–100% duty
TIM10	—	1s tick timer	Drives recipe step timing
LD2 (LED)	PA5	GPIO Output	Status indicator
B1 (Button)	PC13	GPIO Input (falling edge)

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📐 Recipe Profile

The roast profile is defined as an 18-step lookup table steps_lookup[18][4]:

Step	Status	Hold Time (s)	Target Temp (°C)
0	STANDBY	30	0
1	WARMUP	31	20
2	WARMUP	33	30
3	WARMUP	60	40
4	WARMUP	120	50
5	WARMUP	90	60
6	WARMUP	180	70
7	WARMUP	130	80
8	WARMUP	184	90
9	WARMUP	98	100
10	WARMUP	220	110
11	WARMUP	60	120
12	WARMUP	180	130
13	WARMUP	90	140
14	WARMUP	90	150
15	ROASTING	180	160
16	COOLING	60	20
17	COMPLETE	60	20

⚠️ A 2°C hysteresis offset (TEMP_OFFSET) is applied when checking step advancement to compensate for slow PID thermal response.

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🌡️ Temperature Decode

The PID controller returns temperature over Modbus as a raw 2-byte hex value. Decoded manually with no external libraries — each byte is split into high and low nibbles, each nibble is weighted (×4096, ×256, ×16, ×1), summed and divided by 10 to produce degrees Celsius.

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💨 Fan Control

PWM duty cycle is linearised as 0–100% mapped to CCR1 values 0–999 (TIM3 period = 999):

State	CCR1	Duty
STANDBY	0	0%
WARMUP	999	100%
ROASTING	999	100%
COOLING	700	70%
COMPLETE	0	0%
STOP	0	0%
FAULT	700	70%

🔒 FAULT state keeps the fan running as a thermal fail-safe.

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🚀 Getting Started

Prerequisites

• STM32CubeIDE installed
• arm-none-eabi-gcc toolchain
• NUCLEO-F4xx board
• ST-Link V2 (on-board)

Build & Flash

# Clone the repo
git clone https://github.com/gitFrank77/Coffee-Roaster.git

# Open in STM32CubeIDE
# File → Import → Existing Projects into Workspace

# Build: Project → Build All  (Ctrl+B)
# Flash: Run → Debug  (F11)

Debug Output

Connect via ST-Link Virtual COM Port at 115200 baud to see runtime state and temperature readings.

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⚡ Power & Debug Interface

Interface	Details
Power Input	USB 5V
Programmer	ST-Link V2 (on-board NUCLEO)
Debug UART	USART2 @ 115200 baud, Virtual COM Port

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🧰 Toolchain Setup

Component	Version / Tool
Compiler	arm-none-eabi-gcc
IDE	STM32CubeIDE
HAL	STM32F4xx HAL
Protocol	Modbus RTU over RS-485

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🪛 Jumpers / Configuration

Jumper	Setting
BOOT0	0 — Normal boot from Flash
JP1	Closed — 5V via USB

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⚠️ Known Issues / Future Work

• timer_restart flag not yet toggled by TIM10 IRQ callback — step timing reset needs wiring up
• Recipe profiles are hardcoded — future: load from external storage (SD card / EEPROM)
• Set up proper enclosure
• Use modbus lib for RTU communication between PID controller and MCU.

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📄 License

This project is licensed under the MIT License.