Reflow Oven Controller (Arduino)

A compact and robust reflow oven controller for Arduino featuring:

• Dual NTC 100k B3950 thermistors (A0 & A1)
• PID temperature control (PID_v2) with auto-tuning (sTune)
• 16x2 I²C LCD display (LiquidCrystal_I2C)
• Two buttons for mode selection and control
• Buzzer feedback
• Active-LOW SSR output (PWM control)

Implements a standard reflow profile:
Preheat → Soak → Reflow → Cooldown
plus a PID auto-tuning mode.

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✨ Features

• Dual temperature sensing with averaging and smoothing
• PID control with auto-tune
• Simple 2-button UI with buzzer feedback
• LCD display with temperature, setpoint, state, and timing
• Built-in safety temperature limit
• Modular reflow phase logic

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🧰 Hardware

Bill of Materials

• Arduino Uno / Nano
• 2 × NTC Thermistors (100 kΩ @ 25 °C, B3950)
• 2 × 100 kΩ resistors
• SSR (zero-cross AC type)
• 16x2 I²C LCD (0x27 by default)
• Piezo buzzer
• 2 × momentary buttons

Pinout

Function	Pin	Notes
Button: Select	D10	INPUT_PULLUP
Button: Start/Stop	D9	INPUT_PULLUP
SSR (PWM)	D4	Active-LOW
Buzzer	D6	tone() used
Thermistor 1	A0	Voltage divider
Thermistor 2	A1	Voltage divider
I²C LCD (SDA/SCL)	A4/A5	Address 0x27 by default (change in code if needed)

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📦 Required Libraries

Install via Arduino Library Manager or manually:

• LiquidCrystal_I2C
• PID_v2
• sTune
• Wire (built-in)

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⚙️ Build & Flash

1. Open the sketch in Arduino IDE
2. Select the correct board and port
3. Adjust the analog reference and VCC if needed
4. Upload the sketch

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🕹️ Usage

Modes

Mode	Name	Description
0	Idle	Standby mode
1	Reflow Mode	Runs full temperature profile
2	PID Tuning	Auto-tunes PID parameters

Buttons

• Select (D10) — cycles through modes
• Start/Stop (D9) — starts or cancels the selected mode

LCD

• Top line: temperature and SSR state
• Bottom line: setpoint, PWM, time
• Transition messages during phase changes
• Beeps on start, stop, and completion

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🔥 Default Reflow Profile

Phase	Setpoint (°C)	Time (s)
Preheat	100	60
Soak	150	90
Reflow	180	40
Cooldown	0	10

• cooldown_temp = 40 °C
• tempLimit = 200 °C

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🧠 PID & Auto-Tune

• PID output range: 0–255
• SSR is active-LOW, so the PWM is inverted
• PID tuning uses sTune:
  1. Select PID Tuning
  2. Press Start with an empty oven
  3. Auto-tune runs and applies new Kp, Ki, Kd
  4. Results are printed over Serial (9600 baud)

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🧪 Sensor Calibration

• Thermistor model: 100k / B3950
• Series resistor: 100k
• Adjust constants in the code if your hardware differs.
• Optional 2-point calibration (0 °C & 100 °C) for improved accuracy.

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🧾 Serial Output

• Baud rate: 9600
• Logs phase transitions, PID tuning results, and emergency stops.

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🛡️ Safety

• Use properly rated SSR and fusing.
• Keep mains wiring enclosed and grounded.
• Set a safe tempLimit for your oven.

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🧭 Troubleshooting

Issue	Cause	Fix
LCD not displaying	Wrong I²C address	Change address (e.g. 0x3F)
SSR stuck ON/OFF	SSR logic mismatch	Adjust inversion in code
Tuning unstable	Parameters too aggressive	Adjust outputStep or inputSpan
Overshoot	PID values too high	Retune or lower gains

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⚡ Quick Config Reference

• Phases: preheat_setpoint, soak_setpoint, reflow_setpoint
• Limits: tempLimit, cooldown_temp
• PID tuning: inputSpan, outputStep, settleTimeSec

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📜 License

Add your preferred license here (e.g., MIT).

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🙏 Acknowledgments

• Brett Beauregard — PID library
• sTune library authors
• Reflow community projects for inspiration

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