Timothy Woo edited this page Nov 29, 2018 · 58 revisions


First off, let's briefly explain a circuit board is assembled. To aid in the explanation, let's take the analogy of baking a pizza. First of all you'll need the crust, which for us is a bare printed circuit board (PCB) made with different layers of a plastic substrate and copper traces that make the electrical connections. Next, we'll need the cheese that holds everything together, which for us is solder paste (yes, solder in the form of a paste) which "reflows" (solidifies or cures) at a high temperature. The solder paste is applied to the exposed copper pads on the PCB by way of a stencil that is aligned over the PCB. Then we'll grab some toppings, the electrical components, and place them in their appropriate locations on top of the solder paste. The final step is to bake our "pizza" so that the "cheese" holds all the components in place to yield our final assembled board! This is where the Reflowduino project comes in...


The Reflowduino project is an entire do-it-yourself (DIY) reflow ecosystem consisting of open-source hardware specifically built to make it easy to control reflow appliances and apply PID temperature control while maintaining full flexibility in programming and usage while offering a bunch of features.

Since I'm a firm believer of great online resources having learned everything on my own aside from my Mechanical Engineering degree, I'm sharing all of this as completely open-source for everyone to enjoy, including EAGLE PCB files, Arduino IDE example code, sample Android app for Bluetooth control, and full tutorials on how to modify a toaster oven to start cookin’!

That being said, I do offer the boards listed below for sale on my website. Each order helps me out a little bit in creating and sharing new projects with everyone! :)

Safety Disclaimer: If you are a beginner in electronics or don't have the proper experience to work with mains voltage, I would suggest that you either don't mess with it, consult a professional, or keep learning until you're proficient enough! I am not liable for any mishaps that may occur due to misuse of the Reflowduino or its associated components or electrical system (including mains power). Take all safety precautions as necessary, such as gloves and certified safety glasses. Moreover, it is not recommended that you use the same appliance to reflow PCB's and also to cook food for consumption, which may result in food poisoning, especially with leaded solder. You are fully responsible for your actions, and perform them at your own risk!

That being said, DIY away my friends... have fun and stay safe!

Reflowduino Basic

The classic Reflowduino board is an all-in-one Arduino-compatible controller board that can easily transform a toaster oven into a reliable reflow oven! It sports a versatile ATmega32u4 microprocessor with micro USB programming interface, an integrated MAX31855 K-type thermocouple interface with noise filtering, Bluetooth Low Energy (BLE 4.0) for easy pairing with a mobile device, LiPo battery charging and status indication, and buzzer for playing your favorite melodies.

In case you want to order your own boards, here's the shared OSH Park project link

Reflowduino Pro

Although it is more or less retired due to a lack of user demand, there's another version, the Reflowduino Pro board which is just the Reflowduino Basic but with an added solid-state relay on-board:

ESP32 Add-On Module ("Reflowduino32")

With the onset of the ESP32 craze I also created an ESP32 "backpack" module that plugs into this common "DOIT" ESP32 development board to give it convenient thermocouple and relay interface for easy reflow control while still communicating over Bluetooth Low Energy, but this time using the ESP32's built-in Bluetooth.

You can also order this from OSH Park with from project link

Sidekick Relay Module

To make it super easy to control practically any high-power AC appliance I also designed a high-power solid-state relay module which I fondly dubbed the "Sidekick" because it perfectly complements the Reflowduino or Reflowduino32 boards for reflow applications.

In case you want to order your own PCBs, here's the OSH Park project link

Reflowduino Tech Specs

The Reflowduino comes in two varieties, the Reflowduino Basic which doesn’t include a solid-state relay (think Arduino Uno form factor), and Reflowduino Pro, which has a solid-state relay already mounted on-board. Below are some quick technical specifications for the Reflowduino:

  • ATmega32u4: This nifty little microcontroller is the same powerful brains of the well-known Arduino Leonardo with USB-to-serial conversion all handled inside the chip! The board operates at 3.3V, not 5V, so please use level shifters if you are interfacing the Reflowduino with 5V logic!
  • Micro USB Connector: A micro USB powers the board, charges a LiPo battery (if it's there), and can also be used to program the board.
  • Resettable Fuse: The Reflowduino uses a resettable PTC fuse rated at 750mA to protect your board from drawing more than that amount of current from the USB port! Simply removing the short (assuming this was causing the problem) will "reset" the fuse back to normal!
  • Indicator LED's: A green power LED lights up whenever the board is powered (either by micro USB or by a LiPo battery); a blue LED flashes when the Reflowduino isn't connected via Bluetooth and turns solid when a connection is made; and a user-controlled red LED can be used for debugging, or, the in case of the Reflowduino demo code, can be used to indicate whether the reflow process is underway.
  • Voltage Regulator: The Reflowduino has a 3.3V/600mA regulator for powering the ATmega32u4, Bluetooth module, and other things that you might want to connect to it!
  • Thermocouple Interface: The board includes a MAX31855 thermocouple-to-digital converter chip for reading temperature via a K-type thermocouple (included with any Reflowduino purchase).
  • Bluetooth: An HM-11 Bluetooth 4.0 Low Energy (BLE) module allows easy-to-program wireless communication and real-time data transfer between the Reflowduino and a mobile app, eliminating the need for expensive displays that use up a bunch of GPIO pins and eat up space! The Bluetooth can also be used to enable custom functions and user interfaces from the open-source app, allowing for endless possibilities! By default the app shows the real-time thermocouple temperature, graphs the reflow temperature in real time, shows when the reflow process if complete, and saves the data for you to analyze later. These features can be expanded to work with display shields, custom Bluetooth applications for other operating systems, special button functions, and more!
  • LiPo Battery Charging: A 2mm JST battery connector and charging circuit allows you to use a standard single-cell 3.7V LiPo battery with a capacity of at least 250mAH. You can either keep the Reflowduino plugged in via micro USB or use a LiPo battery, or both! If both are plugged in, it will automatically use the micro USB power. The charging current is 250mA by default, but you can solder a jumper to set it at 500mA.
  • Solid State Relay (Pro version only): The Reflowduino Pro comes with an opto-isolated solid-state relay rated at 25A/240VAC (max specs with convection cooling) or 10A/240VAC (which translates to 20A/120VAC) without active cooling, which is all you should need since your outlet can only supply 15A before tripping (at least in the US). If you get the Reflowduino Basic you will need to purchase your own solid-state relay, but no worries; the board has large, easy-to-solder pads that can be used to wire up the relay without tangling up the rest of your project! The board also has a solder jumper where you can cut the default 3.3V relay control trace and bridge a new trace to the USB voltage (5V) in case your external relay input won't operate at 3.3V.
  • Buzzer: A piezo buzzer lets you know when dinner's ready, or you can have it play lullabies!

Other Stuff

  • Arduino Compatibility: The Reflowduino is fully Arduino-compatible and can be programmed using the Arduino IDE with a simple micro USB connection.
  • Pinout and Headers: The Reflowduino uses the familiar Arduino header layout as well as matching mounting holes (3.2mm holes). The pinouts are labeled the same as the Arduino Leonardo, except for the notable exception of the "VIN" pin, which isn't connected by default on the Reflowduino because the battery is only meant to be plugged in via the battery connector. However, there is a solder jumper to connect this pin to 3.3V which may be convenient for another sensor, etc. Also, the "5V" pin on the Reflowduino is the USB voltage (which should be around 5V).
  • Customization: Since the Reflowduino can be used like any other Arduino-compatible development board, you can add shields, sensors, LED's, displays, and more, and Bluetooth makes this especially versatile to interface with your phone or computer. Tinker away and be sure to share your cool projects with everyone!
  • Documentation: I'm a huge fan of detailed documentation, so I've prepared a comprehensive wiki and all the resources you'll need: electrical schematics, EAGLE PCB files, example Arduino IDE code, an open-source Android demo app using Thunkable, starter guides for transforming your toaster oven with Reflowduino, and more!

Sidekick Tech Specs

The Solid-State Sidekick Relay Module ("Sidekick" for short) is a solid-state relay module that allows for quick and easy control of almost any AC appliance, including toaster ovens, hot plates, AC lighting, and motors. Simply plug the appliance into the Sidekick, plug the Sidekick into the wall with the included C13 power cable, and connect the two relay input wires to the Reflowduino. The low-voltage relay input makes the Sidekick microcontroller-friendly for use with any 3.3V or 5V microcontroller, so it will definitely work with other projects as well!

  • Relay control voltage: 3-15VDC, perfect for any 3.3V or 5V microcontrollers! Note: the Sidekick uses the same solid-state relay that is on the Reflowduino Pro and a screw terminal allows for easy and secure connection of the two control wires.
  • Output rating: 12-280VAC output voltage range with current rating of 25A/240VAC (max spec with convection cooling), 10A/240VAC typical, or 20A/120VAC (good for any home appliance in the US).
  • Module power: Accepts a standard C13 power cord (included) that plugs in to the matching C14 connector on-board while the other end plugs directly into a wall outlet. The device connects the ground pin for safety.
  • Appliance power: There is a standard NEMA outlet for the controlled appliance. The appliance is only switched on when the relay is activated (and when the power switch is on of course).
  • Power switch: The module has a power switch that shuts off or enables the whole shebang.

Reflowduino32 Tech Specs

The Reflowduino32 is an add-on module that gives the DOIT ESP32 development board thermocouple and relay interfacing for easy reflow control. Currently it's only designed for the DOIT ESP32 dev board but if you happen to find another board with the same pinouts and 1-inch header spacing then please let me know because that should work too!


  • Thermocouple Interface: Like the Reflowduino board the Reflowduino32 also has a MAX31855 K-type thermocouple IC on-board and a screw terminal provides convenient and secure connection of a K-type thermocouple (included in any Reflowduino32 purchase).
  • Relay Interface: The second screw terminal provides an interface to a relay module (like the Sidekick) to switch the relay on and off with the ESP32 to control the reflow apparatus (toaster oven, etc). The default relay input voltage is 3.3V (works great with the Sidekick) but this can be configured to the VIN voltage (~5V with only USB connected) for relays that don't accept such low control voltages.
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