Wiring
The only thing you need to do to control the oven is connect the two relay output wires appropriately. All the Reflowduino does is control the live (L) wire from the AC outlet on/off while the other neutral (N) prong is always connected. In the US the live prong is the straight, narrower prong whereas the neutral one widens at the end. When the controlled "leg" is connected, power flows to the oven (or hot plate). The following diagram shows the general wiring scheme:
Please note that this control scheme is exactly the same for hot plates. For the Reflowduino Basic you will have to connect an external solid-state relay to the relay control pads on the Reflowduino:
Since the Reflowduino Pro already has a solid-state relay on-board, you have one less piece to worry about but the fact that there are no easy plug-in connectors means you'll have to do some soldering:
Perhaps the easiest way of controlling the appliance is with the Sidekick relay module and Reflowduino Basic in which no custom wiring is needed:
Just as simple is to use a DOIT ESP32 dev board with the Reflowduino32 backpack module and Sidekick:
IMPORTANT DISCLAIMER: Again, if you don't know what you're doing, please do not attempt this! All actions are are you own risk. It is not recommended to use this setup for extended usage and this was used for demonstration purposes only! If you attempt this project please solder the wires and use proper insulation and take proper safety precautions like certified safety glasses and gloves. Never adjust wiring with the power cord plugged in!
For hot plates with a single temperature control knob you can either choose to break open the device and bypass the temperature knob or you can simply turn it to max it out at HIGH. The reason this works is because the temperature control operates on thermal expansion of metal contacts inside. By turning the the knob to the highest setting you're simply allowing the the device to always conduct, which is just what we want since the Reflowduino will be taking care of the control anyway. If you want you can permanently glue the knob to HIGH if you think you'll forget to check it. This method leaves us with only the power cord to worry about! Below is a test setup I used for the hot plate:
Here's a closeup of part of the wiring:
If you are using the Reflowduino Basic along with the Solid-State Sidekick you simply only have to plug in the hot plate's power cord into one of the provided receptacles; solder wires from the Reflowduino's "RLY+" and "RLY-" pads and secure them in the relay module's screw terminals; and finally, plug in the relay module itself and turn the switch on!
In order to keep the thermocouple pressed against the hot plate, I used a large wrench socket which I placed on top of the metal thermocouple tip. This turned out to work quite well. However, a more permanent solution would be to drill a hole and fasten the thermocouple with a metal shim attached to the hot plate using a screw.
This video shows the app collecting and graphing the data via Bluetooth.
Fortunately the same knob hack works with toaster ovens! You can simply max out the temperature knob,
turn the cook setting to "Bake" (which means top and bottom filaments will be on),
and turn the timer knob to "Stay on":
This works because in this setting the toaster will always be on if you plug it directly into the wall and the Reflowduino will just be allowing it turn on or remain off. If this is going to be permanent, glue the knobs if you need to!
If you feel adventurous and are itching to take apart the toaster oven in the name of science, more power to you! Anyway, let's take a look!
Here's how my toaster oven looks like on when placed up-side-down on the table:
There were a total of fifteen screws that I had to take out, including the four plastic feet. The two front feet of the oven have little rubber caps that sit in them, so pry those out to reveal the screws underneath. There is also one screw sitting behind each of the front feet that aren't visible in the picture. After unscrewing all the screws I was able to slide the black casing out and away from the toaster.
Now that the casing is gone, here's a look at the inside. (Be careful, the sheet metal can be sharp and there are screws poking out in some places!) The power cord comes in from the hole at bottom right of the picture and gets spliced via two screw caps into the rest of the circuit. There are two heating elements (top and bottom) and these are wired up to the knobs so that they can be controlled independently (like broil vs bake, etc).
Both heating elements are connected on the other side and the return wire is tied directly to neutral:
What we want to do is bypass all the knobs while keeping them intact since I don't have any plans for mounting anything in their place. Also, most people like to put their controllers inside the toaster oven enclosure, but I think it's easier, safer, and more convenient to simply place all the controls outside and control the oven from the power cord rather than from the inside. So instead of splicing the live wire inside the toaster I'll bypass all the knobs on the inside by disconnecting the knobs that are attached to the live wire (the red wire in the picture) and connecting the two heater tubes together to the live wire. This means that after the tweaks and without the Reflowduino the oven will turn on at max power when you plug it in! However, you're free to do whatever suits you best. Also keep in mind I'm also working on making a custom junction box that will allow everything to be connected simply by plugging things into the box so really the only work would be to bypass the knobs inside!
Since the wires on the heater filaments are spot-welded (because they normally get hot and could potentially melt solder) we can't just solder a wire from the upper tube to the bottom tube. Instead, we need to disconnect them from the knobs and connect them via those locking connectors. I ended up using two wires joined together at the power cord's live wire (bottom right) and two blade crimp connectors on the other ends that snapped into the two wires from the top and bottom heater tubes. Please note that for this particular toaster oven you must use the white wire connected to the bottom tube rather than the black wire because the black wire actually has a large diode on it (the tricky bastard...) and using that wire will result in sore disappointment when only the top filament turns on!
I disconnected the red wire (which runs to a knob) and protected it with a bit of heat shrink tubing. Before soldering the connections it is a good idea to slip the heat shrink tubing over the wires so that you don't bump your head in the wall later!
Here's the finished wiring:
After all the wiring was complete, test the oven by plugging it directly in to a power outlet. Both heating filaments should turn on. If they do, unplug it and you're ready to switch the live wire with the Reflowduino! Using the same connections as shown in the previous page of this tutorial connect the toaster's neutral wire directly to the the wall's power cord while putting the Reflowduino (or relay) in series with the live wire. Again, I'm in the process of making a custom junction box just for this purpose! Here's my setup using alligator clips:. Also note that I didn't bother permanently attaching the thermocouple to anything, but simply shut the door gently against the thermocouple wire with the tip resting on the drip tray that I used as the reflow pan.
If you are concerned about any temperature error that may be associated with simply holding the thermocouple against the door, you can simply use a scrap PCB with a couple holes (or you can drill them yourself since it's scrap anyway) and thread the thermocouple into the holes so that the tip ends up in one hole, then just place the PCB alongside the one you are reflowing. This ensures a more comparable temperature reference.
You're ready to go! Connect your phone to the Reflowduino and start cooking! Check out these videos showing this setup in action: