Preparation
NOTE: The Reflowduino Pro has been retired and is no longer available for sale but this wiki still documents it. Please use the Reflowduino (Basic) or ESP32 and Reflowduino32 backpack module.
You will need the following parts to turn a toaster oven into a PCB reflow oven:
- Reflowduino Pro OR
- Reflowduino Basic + Sidekick relay module (comes with thick power cable) OR
- DOIT ESP32 development board + Reflowduino32 Backpack Module + Sidekick relay module
AND
- K-type thermocouple (included with the Reflowduino or Reflowduino32)
- Controller power source. For Reflowduino: LiPo battery, 5V micro USB (from a laptop or adapter), or both! For Reflowduino32: Micro USB or external voltage on VIN and GND pins.
- Toaster Oven OR hot plate (toaster preferred). For higher-end builds you can use a convection toaster oven.
- Small flat head screwdriver (for the screw terminals)
- Smartphone or Bluetooth-enabled device. For now, the app is only for Android. Maybe you all can help me develop apps for other platforms!
- Optional: something to hold the thermocouple down, like a scrap PCB. This may yield more accurate readings.
- Optional (for Reflowduino): a laptop to collect and graph data in real time!
The following items are needed only if you want to do lots of customization to your reflow oven build (not needed in most cases):
- Screwdriver (for taking the toaster oven apart)
- Wire cutters and pliers
- Soldering iron and solder
- 14-18 AWG wire (stranded wire is easier to deal with)
- Appropriately-sized heat shrink tubing for insulating wires. Depends on your setup.
- Optional drill and drill bit to make a hole for the thermocouple
- Safety glasses (stay safe, we're dealing with mains voltages here!)
- Gloves (the sheet metal of toaster ovens can be sharp and ridden with screws poking out everywhere!)
- Skillz
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 PCB's or its associated components and electrical system (including mains power, breaker panels, etc). Take all safety precautions as necessary. Moreover, it is not recommended that you use the same appliance to reflow PCB's as to cook food for consumption. This may result in food poisoning, especially if you use leaded solder for your PCB's. You are fully responsible for your actions, and perform them at your own risk!
Below is a description of each item in more detail.
An easy way to get started is to use the Reflowduino Basic along with the Solid-State Sidekick, which integrates the solid-state relay and the receptacles for easy connection! An alternative is the Reflowduino Pro which has a solid-state relay mounted in a single board, which would allow you to customize a bit more since you do the wiring yourself.
Another equally-simple alternative is to use the ESP32 dev board along with the Reflowduino32 backpack module which simply plugs into the ESP32 dev board. The core functionalities of using the ESP32 are practically the same as the traditional Reflowduino method except that this method uses the built-in Bluetooth Low Energy feature of the ESP32, which is pretty neat! (I suppose you could also make a WiFi version as well)
A quick note on the ESP32 dev board: The dev board I chose was the "DOIT" ESP32 dev board because it seems to be readily available and widely used. However, if another ESP32 board has the same pinouts and pin spacing it should work as well. If you find such an alternative please let me know so I can tell others!
The thermocouple measures the temperature inside the oven (yes, very hot!) and needs to be a K-type thermocouple.
- Loosen the screw terminal on the Reflowduino board with a small screwdriver
- Slightly peel back the outer insulation of the thermocouple covering the insulation of the two individual wires. You should then be able to see
- Take note of the polarity written next to the screw terminal (red and yellow)
- Insert the wires into the screw terminal and secure by tightening the screws
The Reflowduino Pro is equipped with a solid-state relay that operates within a control voltage range of 3-15VDC and can handle up to 25A with proper forced convection cooling. Normally it can handle 10A at 240VAC (or 20V at 120VAC) continuously, which is enough for any appliance in the US since the breakers trip at 15A.
If you have a Reflowduino Basic and want to interface it with a relay, a good option would be the Solid-State Sidekick which allows you to simply connect the "RLY+" and "RLY-" pins on the Reflowduino to the screw terminal on the relay module and plug in the controlled appliance. However, in the end you're free to choose your own relay!
The term "solid-state" means that there are no physical, moving parts inside that are making contact, unlike conventional contact relays. Make sure that you choose a solid-state relay because conventional ones will make a clicking sound every time they're switched and are not suitable for high-frequency switching (like PWM applications). Moreover, they have a limited lifetime, especially at higher voltages and switching frequency.
You might also see "opto-isolated" show up in the description, as in the Reflowduino's relay. These relays use an opto-isolator, which is basically a device in which the relay is optically-controlled by an infrared LED that turns on and off. This means that there is physical isolation between the mains voltage (120V/240VAC) and the input control voltage (DC in our case) and therefore increases the level of safety.
If you are selecting your own Solid-State Relay (SSR) you will need to make sure that it can be controlled at low voltages since the Reflowduino operates at 3.3V, especially since most large relays that control mains power (120V/240VAC) don’t operate at low control voltages, especially 3.3V. However, as mentioned in the product overview tutorial you have the option of cutting a trace and soldering a jumper to select 5V instead of 3.3V to control the relay, but you will need to plug in the Reflowduino via micro USB since a LiPo battery alone won’t be sufficient.
Another thing you should consider is the output current and voltage ratings of relay. The Reflowduino Pro’s relay can handle up to 25A at 240VAC with proper forced convection cooling. Without such cooling it can handle 10A/240VAC continuously, which should be adequate for most purposes, especially in the US where 120VAC is the standard. Additionally, the PCB design incorporates wide top and bottom copper planes to dissipate heat through a multitude of vias. Please note that these planes may get hot during normal operation.
Zero-crossing is a feature that some relays have to minimize load spikes and ensure smooth control of a device by waiting until the AC waveform crosses zero, at which point the relay turns it on. Usually these relays can cost a pretty penny (like $8-$10) more than others without zero-crossing. Since the Reflowduino control scheme uses a discrete on/off control of the relay and not a continuous PWM control, zero-crossing isn’t critical and the relay on the Reflowduino Pro doesn’t have this feature. However, if you select your own
When shopping for a toaster oven you will need to look for a few things:
- Heating elements: The more heating elements the better, as this will give a more uniform heat distribution. If you look at Amazon reviews and people say it can’t even toast a slice of bread in 10 minutes, please don’t buy it. Also, convection toaster ovens will yield a much better thermal distribution throughout the chamber than conventional toaster ovens, which is especially important when reflowing larger batches at the same time.
- Metal tray: You will need a flat metal tray on which to put the PCB if the toaster oven doesn’t already come with one. This is because placing the PCB directly on the grill piece will not heat up the PCB uniformly (the spots directly on top of the grill lines will be hotter than the rest).
- Simple: Unless you’re wanting to make your project look like a futuristic space craft you really don’t need tons of knobs, switches, and controls. This will likely just make your life harder because these functions might need to be disabled or bypassed in order to control it with the Reflowduino. Simple and small also usually means less expensive!
- Small: The smaller the oven, the more efficient and the more responsive to the control. Choose the right size for the kinds of PCB’s you will be making!
- Power rating: Generally 1000W – 1500W should be good enough but it could depend on the configuration.
Personally I used this 1100W Hamilton Beach toaster oven from Walmart which I bought for about $21 at the time.
This toaster oven actually feels quite decent and it comes with a grill, cooking tray, and drip tray.
The cooking tray has a crazy bumpy pattern on it which is certainly not ideal for reflowing so I decided to simply toss aside both the metal grill and the main tray and just use the drip tray instead! It turned out to be perfect for what I need because the drip tray is nice and flat for most of it and it's thin as well. Eliminating the metal grill and cooking tray reduces the amount of metal that needs to be heated up during reflow, which means better temperature control.
Bingo!!! Time to start cookin'!
Some people retrofit their ovens with thermal insulation like fiberglass blankets placed around the oven cage when you take the oven apart, or some aluminum foil on the door (with a slot to peer through). This will allow your toaster oven to heat up quicker since it will retain the heat, but this also means it will cool down more slowly so you might have more temperature overshoot without opening the oven door fast enough!
Instead of using a toaster oven you might choose a hot plate! These are even less expensive than toaster ovens and are very compact so they might be just what you want, and the control principle is exactly the same. However, these plates may not be suitable for temperature control due to high thermal mass of the plate. I personally tested the Reflowduino with this Aroma hotplate which I bought for only a little over $18 on Amazon. (NOTE: Please see the test results for this hot plate here to decide if this is OK for your application because it is not capable of heating up or cooling down quickly) This particular hot plate is 120V/1000W so it draws about 8.3A of current.
(Note: this picture is from the seller)
When selecting a hot plate it is a good idea to select one that has a flat, uniform surface as much as possible. Most hot plates have a small circular part in the middle of the plate that is slightly recessed. Try to get one that minimizes this recessed region so that you can have a larger usable area to place your PCB's on. Also, the simpler the better! Try to get one that only has a single knob. Other than that, most hot plates should work!
Some people (like "Winston" on this Hackaday post) have used electric skillets which actually sounds like a great idea (at least better than a hot plate) because it has both a flat surface and you can even cover the top to let it simmer! If anyone has more specifics on this, feel free to share!