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PID-Controlled SMT Reflow Oven Controller

Prototype a reflow oven controller that measures oven temperature and drives the heater safely and repeatably.

Advanced Project — A reflow oven combines mains switching, high-temperature sensing, thermal control, isolation, and safety-critical firmware, which makes it significantly more complex than a typical hobby embedded project.
Assumptions:
  • You are building a benchtop prototype, not a certified appliance.
  • The oven already has a mains heater element and fan; the electronics will switch the heater on/off or via burst-fire control.
  • You want local control and display, not WiFi/cloud connectivity.
  • A single temperature sensor is acceptable for the first prototype, though a second safety sensor would be wise in a later revision.

Bill of Materials

Microcontroller
Top Pick SAMD21G18A Microchip From our database
ATSAMD21G18A is the best overall pick here because it gives you enough flash and RAM for a robust reflow state machine, display handling, and safety logic without being overkill. It also has native USB and the I2C/SPI peripherals you need for the temperature sensor and display.
Digikey $4.07 (1,146 in stock)
Dev Board 102010388 Seeed Technology Co., Ltd
Ready-to-use board for prototyping with this chip
Digikey $6.50 (352 in stock)
ATmega328P Microchip Technology From our database
Very common and inexpensive, with huge Arduino ecosystem support for simple heater control and sensor reading. Best if you want the simplest possible firmware, but it has much less RAM/flash than the SAMD21 options.
Temperature Sensor
Top Pick MAX31855KASA+T Analog Devices Inc./Maxim Integrated From our database
MAX31855KASA+T is the best engineering choice for a reflow oven because a thermocouple-based measurement system is far more appropriate than a PCB-mounted ambient sensor at 220 C to 250 C.
Digikey $10.91
MCP9808 Microchip From our database
Higher-accuracy I2C temperature sensor that is widely used for precision measurement. Good for a prototype reflow controller when you want a straightforward digital sensor and do not need thermocouple-level temperature range.
Actuator
Top Pick Omron G3MB-202P-DC5 Omron
For a first reflow oven, a zero-cross SSR is usually the fastest path to a working and safer build.
Digikey $4.80
SY21634FCC Silergy From our database
Integrated half-bridge driver for inductive loads and switching applications. It is more appropriate for low-voltage loads than direct mains heater control, but it can be useful in a prototype that uses a relay or auxiliary actuator.
Power Supply
Top Pick Mean Well IRM-05-5 Mean Well AI suggestion - verify availability
It pairs well with a 3.3V MCU board and keeps the low-voltage control electronics self-contained.
HLK-PM01 Hi-Link AI suggestion - verify availability
Very small AC-to-5V module often used in embedded prototypes where space is tight. It is convenient, but you should be careful about thermal design, creepage, and sourcing quality in a heated appliance enclosure.
USB wall adapter 5V 1A Generic AI suggestion - verify availability
Simplest option for bench prototyping if you keep the controller completely external to the oven. This avoids mains PSU design entirely, but it is less integrated and not ideal for a final appliance-style prototype.
Display
Top Pick WEA012864DWPP3N00003 Winstar Display From our database
WEA012864DWPP3N00003 is the best display choice because it is compact, easy to interface, and large enough to show the key reflow information clearly. It is a straightforward match for a prototype front panel.
Digikey $7.35 (629 in stock)
DFR0650 DFRobot From our database
0.96 inch 128x64 OLED breakout with I2C/SPI support, ideal for rapid prototyping. Easy to wire and widely used for status displays, though the small size limits how much process information you can show at once.
PEC11R-4215F-S0024 Bourns From our database
Rotary encoder with push switch for user input rather than a display, but it is useful as the main front-panel control for setting profiles and starting cycles. It is a good companion to a small OLED display in a reflow controller.
User Input
Top Pick PEC11R-4215F-S0024 Bourns From our database
PEC11R-4215F-S0024 is the best input device because a rotary encoder with push switch is the most practical way to set temperatures and navigate a simple reflow menu. It reduces front-panel clutter and is easy to use with an OLED.
Digikey $2.95 (4,519 in stock) Mouser
Tactile pushbutton suitable for dedicated start, stop, and cancel controls. Simple, reliable, and easy to mount on a front panel.
Digikey $0.67 (76,026 in stock)
Apem 5GTH9 APEM
Panel-mount toggle switch that can serve as a hard power or enable switch. Useful as a physical safety control in a heater project.

Compatibility Notes

  • If you use the MAX31855KASA+T thermocouple interface, it connects over SPI and is a much better match for reflow temperatures than the board-mounted digital sensors.
  • The display and encoder are both low-speed digital interfaces and are easy to share with the SAMD21 on a prototype PCB.

You'll Also Need

  • K-type thermocouple probe and mounting hardware.
  • Mains-rated fuse, IEC inlet, power switch, and emergency cutoff hardware.
  • Heater element, fan, thermal cutoff, and oven enclosure.
  • Proper PCB terminal blocks, high-voltage connectors, wire, heat-resistant sleeving, and strain relief.
  • Opto-isolation or safety-rated interface circuitry if you do not use a prebuilt SSR module.
  • Front-panel mechanical parts, knobs, standoffs, and enclosure cutouts.
  • Calibration equipment or at least a reference thermometer for validating the temperature profile.
Estimated BOM Cost: $45-55 (based on live distributor pricing)
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Design Considerations

Temperature Measurement Strategy
For a reflow oven, a board-mounted ambient sensor is usually the wrong tool because the chamber can exceed 230 C and the sensor placement will lag the actual PCB temperature. A K-type thermocouple with a dedicated interface IC is the normal approach because it survives the temperature range and responds quickly enough for profile control. If you only measure air temperature, expect poor repeatability and overshoot on real boards.
Heater Control Method
For a prototype, zero-cross SSR burst-fire control is much easier to implement than phase-angle control and creates less EMI. Use a control window on the order of 0.5 to 2 seconds so the heater duty cycle can be adjusted smoothly without rapid mains switching. Add a hard thermal cutoff independent of firmware so a software fault cannot leave the heater on indefinitely.
Safety and Isolation
Treat the heater side as mains equipment: separate low-voltage and high-voltage grounds, maintain creepage and clearance, and use an isolated AC-to-DC supply. Put the fuse and power switch on the line side, and make sure the enclosure cannot expose live parts. A reflow oven is a fire-risk appliance, so a watchdog and a hardware overtemperature cutoff are not optional in practice.
Firmware State Machine
Implement the reflow profile as a state machine with preheat, soak, reflow, and cool-down states rather than a single PID loop. That makes it easier to enforce time/temperature limits and to log or display the current stage. Add a watchdog timer and a sensor-fault state so a disconnected probe or invalid reading forces the heater off.
Validation and Calibration
Do not trust the first temperature curve you see on the display. Validate with a reference thermocouple or external logger at multiple points in the chamber, because airflow and heater placement can create large gradients. Tune the profile using real solder paste and scrap boards, then verify repeatability across several cycles before using valuable assemblies.

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