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. Also, for the Reflowduino Basic you will have to connect an external relay to the relay control pads on the Reflowduino.
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 something like this enclosed relay with the Reflowduino Basic, 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! (NOTE: I haven't personally tried that relay module myself) I'm currently working on a junction box for the Reflowduino Pro that will simplify the wiring and consolidate everything as a single box!
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.
Toaster ovens are a little harder to work with (but not much harder) than hot plates since they have multiple knobs and these knobs don't only control temperature. Also, depending on if your controller is going to be inside the toaster oven enclosure you might want to drill a hole for the thermocouple to be routed to the inside the oven. 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 thirteen 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. After unscrewing all the screws I was able to slide the black casing out and away from the toaster.
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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).
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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!
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