Background

Hi everyone, I'm Timothy Woo, a young engineer with a passion for electronics, cool IoT devices, and sharing my discoveries with others! A mechanical engineer by trade but an electrical engineer at heart, I am one who scours the Internet, always looking for new things to learn and never running out of ideas to share! As one who has vastly benefited from the do-it-yourself (DIY) electronics community I think it's time for me to give back and share my discoveries with others! This is why I made Reflowduino completely open-source for all to share, collaborate, improve, and learn. To me, this is what electronics is about. "Learn to share, share to learn!"

The art of designing and assembling custom printed circuit boards (PCB's) has long been restricted to manufacturers or die-hard individuals etching their own boards in a university lab, but with the advancement of technology and affordable one-off prototypes this has become an increasingly popular (and incredibly useful) skill in hobbyist electronics. With the emergence of the amazingly small but powerful surface-mounted technology (SMT) in the electronics industry, traditional through-hole mounted (THM) components have been phased out in many ways. As a result of this revolutionary change in manufacturing, many electronics enthusiasts are face-palming or giving up on SMT design simply because they don't have the proper equipment, expertise, or willpower to assemble surface-mount printed circuit boards (PCB's).

One of the most fundamental pieces of equipment required for assembling surface-mount circuit boards is the "reflow oven", which is a temperature-controlled chamber that subjects the PCB to a precise temperature profile such that the solder melts and "reflows" properly to ensure reliable component bonding and minimize electrical shorts. However, industrial reflow ovens are very expensive and have closed-source designs that leave little or no room for customization. Instead, hobbyists have leaned toward "hacking" toaster ovens and hot plates to transform them into reflow apparatus, but unfortunately this still requires quite a bit of work, typically including messing with mains power (wall outlet) and a rat's nest of wires and modules. Thankfully with Reflowduino and the Solid-State Sidekick relay module that's about to change! With Reflowduino the goal is to make it possible for anyone to affordably assemble their own circuit boards at home with high-quality results while having access to detailed documentation and community support for widely-used development platforms. 

Introducing: Reflowduino

Reflowduino is an affordable, completely open-source, Arduino-compatible PCB reflow oven controller that can painlessly transform a $20 toaster oven into a reliable reflow oven for PCB assembly. To best cater to the needs and different experience levels the Reflowduino comes in two flavors: the Reflowduino Basic, which doesn’t include a solid-state relay, and the Reflowduino Pro, which has a solid-state relay already mounted on-board (pictured above).

With pretty much everything you'll ever need on a reflow controller, Reflowduino eliminates a tangle of wires and the need for an extensive parts list and even the need for directly dealing with mains power if used in conjunction with the Sidekick relay module (explained later). It is an extremely compact design that sports Bluetooth connectivity for wireless control and data acquisition, provisions for thermocouple temperature-monitoring, and charging for the adored Lithium-Polymer (LiPo) batteries. To top it off, all these gifts are wrapped in a familiar Arduino arrangement and pinouts to allow users to add extra features and "shields" while accessing the wide open-source Arduino knowledge base. Moreover, in the Reflowduino Github repository I've personally compiled learning resources for the Reflowduino using some of the best (and free!) electronics platforms for software development like Autodesk EAGLE, Arduino IDE and Thunkable. I've created a full product wiki on the Github repository and also on places like this Reflowduino Instructable. So much for those excuses of why you shouldn't learn electronics and make your own surface-mount boards!

How Reflowduino Works

The Reflowduino uses a well-documented ATmega32u4 microcontroller as the "brains" of the board which can be programmed in the friendly and widely-used Arduino environment. For the specific application of circuit board reflow the Reflowduino measures the temperature of the reflow oven (or hot plate) via a thermocouple and controls a solid-state relay accordingly in order to make the actual temperature follow a desired temperature profile as closely as possible using Proportional Integral Derivative (PID) control. During the reflow ("baking") process the Reflowduino uses its Bluetooth functionality to send temperature data to a mobile device wirelessly for viewing in real-time and data analysis. When the reflow process is complete the buzzer plays a short melody!

Using Reflowduino

Reflowduino is designed to be extremely easy to use! The general concept is to switch the power of the appliance on or off with a solid-state relay as shown below, measuring the temperature by placing the thermocouple tip inside the oven during the whole process.

With the Reflowduino Pro all that needs to be done is to switch the live wire with the on-board relay:

Wiring with the Reflowduino Basic is similar except the Basic version doesn't come with a relay so one more item is involved. However, in a following section you will see how the Sidekick relay module can fix this very easily!

Reflowduino Specs

Below are some quick technical specifications for the Reflowduino, all of which can be found on the official Reflowduino wiki but are summarized below:

• ATmega32u4: This nifty little microcontroller with a built-in USB controller is the same powerful brains of the well-known Arduino Leonardo. 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 in the case of the Reflowduino demo code, 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) and noise filtering.
• Bluetooth: A 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 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, 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 for larger batteries.
• 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 at night if you have insomnia!
• 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 3.2mm mounting holes. The pinouts are labeled similarly to 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 but could be more or less).
• 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, board design files, example Arduino IDE code, an open-source Android demo app using Thunkable (a free block-based app builder), starter guides for transforming your toaster oven with Reflowduino, and more!

Introducing: Solid-State Sidekick

The Sidekick is a separate solid-state relay module that goes hand-in-hand with the Reflowduino Basic and it's the first solid-state relay module of its kind I've seen that can enable any 3.3V or 5V microcontroller to control 120/240VAC at high currents simply by plugging in the appliance. This means it can control almost any reflow appliance (toaster oven or hot plate) without tweaking it at all! With the knob(s) set properly on the appliance the user can simply plug it into the Sidekick and secure the two relay input control wires from a Reflowduino Basic via a screw terminal and it's ready to be controlled!

The Sidekick Specs

• 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: 25A/240VAC (max spec with convection cooling), 10A/240VAC typical, or 20A/120VAC (good for any 120V appliance in the US). 
• Module power: Accepts a standard C13 power cord 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. Note that if you are in a country that uses 240VAC you will need to get a 120V-to-240V adapter.
• Power switch: The module has a power switch that shuts off or enables the whole shebang.

Choosing a Perk

Contribute to support open-source DIY electronics and get cool perks!

Shipping note: The default shipping method is USPS First-Class in the US or USPS First-Class International Service for international locations. Tracking info for international orders may or may not be available, depending on the country. Please contact me beforehand if you would like to upgrade your shipping option.

There are a few main hardware items to choose from and each perk has its own advantages so I'll briefly explain which one might be most suitable for you!

1. Reflowduino Basic - Does not come with a relay (choose your own)
2. Reflowduino Basic + Sidekick "Control Kit" - Easiest/safest control method
3. Reflowduino Pro - Comes with a solid-state relay already mounted. Good for customization
4. Solid-State Sidekick - All-around useful relay module for controlling AC appliances!

Note: The Reflowduino Basic or Reflowduino Pro comes with a K-type thermocouple (1m long) as well as a loose kit of female headers. You are free to solder the included headers or choose your own!

The first option is great if you want to select your own relay or if your project requires a specific mounting configuration. The second is the easiest, safest way to control almost any toaster oven or hot plate without even needing to tweak the appliance or mess with mains voltages. All you need to do is set the knobs to their proper positions (for example, max temperature, "bake" setting, and "stay on" for the timer) and it's ready to be controlled externally! The third option is great if you would like some sort of customization and do the wiring yourself. This is also the most inexpensive solution to get the job done. Lastly, the final option allows you to get the Sidekick by itself, which can be very useful not only for reflow oven control but for other AC control projects like PWM lamp dimming, AC motors, and more with any 3.3V or 5V microcontroller like Arduino!

Note: Although there isn't an option on Indiegogo to get multiple perks in a single transaction, just go ahead and sum them up and message me with what perks you want and we'll get it figured out!

Risks & Challenges

So far I've created multiple Reflowduino and Sidekick prototypes and have proven that they work! Even before this campaign I have sold several units and have people on the waiting list. This crowdfunding campaign will help me immensely in spreading the word, attracting fellow hobbyists like myself, and to fulfill more orders. Since I manufacture the boards myself for this campaign, fulfilling orders will be exceptionally low-risk because I have the parts inventory and expertise to assemble the units without having to rely on outsourcing production. So yes, your Reflowduino boards will be proudly assembled and tested in the USA!

That being said, there are also other challenges that will need to be faced, including reducing the cost as low as possible so that the Reflowduino will be a ubiquitous piece of equipment in any designer's toolbox and moving the designs forward through extremely expensive certifications like FCC, CC, CE, RoHS, and UL to name a few. However, even now the Reflowduino and Sidekick module are fully-functional and well-documented so I foresee these challenges to be scalable obstacles and I will do my best to fulfill all orders on time before March 2018, hopefully even earlier, especially for early bird orders for which I already have inventory. (Update: all early bird inventory is gone, except for some more Sidekick modules. If there are enough orders I'll restock parts before the campaign ends to get them out early!)

Currently the Reflowduino and the Sidekick are already fully-functional but when quantities exceed my capacity I will need to work with a contract manufacturer to build them and take care of things like PCB assembly, pick-and-place machine setup, quality testing, and packaging. Additionally, I would have to stock up on inventory in order to keep the unit cost down, which is a large up-front investment. However, before I even give the designs to a contract manufacturer I may need to tweak them to meet certifications like FCC, CC, CE, RoHs, and UL, each of which could cost tens of thousands of dollars!

In order to get the Reflowduino and Sidekick to the point where they can be mass-produced, I will need to receive support from gracious donors like you to cover the practical matters. Design work takes time, as does putting together and sharing more resources and handling technical support with you all! Moreover, I'm always on the lookout for new things to create and share and funding this project would give me the moral and monetary support I need to continue the contributions I make in my spare time aside from running a small business.

All in all, your support would greatly assist me in scaling Reflowduino and give me the encouragement I need to create and share more open-source projects. Even if I don't reach my entire funding goal by the end of this campaign, the funds will still go toward producing your Reflowduino units as well as catalyzing my brain to spawn more ideas... stay tuned because I already have some lined up which I plan on launching here soon! Again, the Reflowduino is proven to work but it just needs a strong base of enthusiastic supporters so everything you can do to make this happen is greatly appreciated!

Other Ways to Help

If nothing else, please share this campaign to your friends, family, and anyone who might be interested on social media! Remember that every view counts for me, and I'm depending on you to make this happen!

Q&A

Q: Can you make a reflow oven or hot plate without directly messing with mains power?

A: Yes! If you don't need to customize the insides of the toaster oven or hot plate you can simply control the appliance from the outside (from its power cord) using a Reflowduino Basic and the Sidekick. Doing it this way will avoid messing with the mains voltage altogether and is the safest method.

Q: Can I use the Reflowduino for things other than controlling a reflow oven?

A: Absolutely! The Reflowduino is essentially a 3.3V version of the Arduino Leonardo but with tons of extra features including Bluetooth, LiPo battery management, micro USB interface, buzzer, and thermocouple interface which are specifically useful for reflow control. However, at the end of the day it's just like any other microcontroller in that you may use it for anything else you'd like.

Q: Does the Reflowduino accept Arduino shields?

A: Yes, but make sure it's 3.3V compatible! The Reflowduino is closer to the Arduino Leonardo but it operates at 3.3V instead of 5V like most Arduino boards. This means that you should make sure the shield can operate at 3.3V. Coding for these shields may also be slightly different than other Arduino shields because of the ATmega32u4 microcontroller. If you find one that works please let me know so I can build a list of tried-and-tested shields! 

Q: Does the Reflowduino accept other power sources besides micro USB and LiPo battery?

A: No, the Reflowduino is meant to operate on a 5V micro USB cable or standard 3.7V single-cell LiPo battery. The voltage regulator can only handle an input voltage of up to 6V.

Q: Can I use an Arduino or other 3.3V or 5V microcontroller to control the Solid-State Sidekick?

A: Most certainly! The relay control voltage is 3-15V so if you just wanted to use the Sidekick to, say, control AC lighting, motors, or other appliances, you could just use an Arduino Uno! (Please first consult the laws where you live before attempting a project.)

Q: Can I use the Reflowduino and Sidekick for cooking food items?

A: Good question! Yes, if you also happen to be a nerd who likes perfectly-baked pizza or toast you can program your Reflowduino with the optimal thermal profile (and be sure to share it with us!) to enhance salivation. However, please note that you should NOT use the same toaster oven to both cook food and bake circuit boards, especially with leaded solder paste!

Additional Comments

Please keep in mind that the Reflowduino and the Sidekick have not yet been certified by authoritative entities. Also, the units that I will ship to you will be improved versions so they may not look exactly like the pictures shown! For example, the screw terminal could be green instead of blue, and there will be a cutout between the relay output pads on the Reflowduino Pro for physical separation for safety. Moreover, by purchasing or using a Reflowduino or Sidekick you confirm that you have read and agree to the safety disclaimer below:

Safety Disclaimer: If you are a beginner in electronics or don't have the proper experience to work with mains voltage, you either should not 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 circuit boards 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, stay safe, and share this campaign!

Credits

Thanks to everyone who make this project possible!

• Arrow Electronics as an excellent component supplier and for Arrow Certification!
• OSH Park for perfect PCB's and for supporting Reflowduino!
• Autodesk EAGLE for providing quality PCB design software!
• Thunkable for offering a user-friendly yet powerful app-development interface!
• Adafruit for their MAX31855 Arduino library!
• Fellow DIY'ers from all over the world who like, share, and support Reflowduino!
• Photo Credit: 4-Slice toaster oven photo provided by Hamilton Beach