Nothing new but just an evolution of previous projects, with detailed description of why and how the modifications are executed.

This is a combination of the amazing project of Vulcaman and the great evolution from Polihedron.

I will therefore not repeat the description of the basic operations and details, already extensively explained by Vulcaman and Polihedron.

Supplies

The main list of components is almost the same of the one from Vulcaman, apart:

1-The Nextion display is no more available on Bangood but on Aliexpress

2-The wool rock for thermal isolation and glue are from Amazon

Other components (like buzzer, 12->5 DC-DC regulator, capacitors, diode bridge rectifier, transformer, rock switch, perfboard, fan, etc.) are from my drawer.

Step 1: Mounting Control Board

First of all I mounted all the components on a perfboard. The power supply is obtained from a 220V to 12V transformer (the classic old way) with a rectifier and some capacitor. The 12V power is to supply the fan that extracts heat from the zone with electronics, in order to keep the components, and mainly the Solid State Relay, cool.

The 5V power is from a 20 years old (but still valid) DC-DC Texas Instruments hybrid module (datasheet attached).

To mount the thermocouple adapter more appropriately I desoldered the original pin strip and mounted a vertical one.

As can be seen on the schematic, the project I follow is that of Polihedron, which adds the buzzer, very useful to quickly knowing when the cycle is finished and it's time to open the door. Unlike that, I didn't use the level shifter to drive the solid state relay. Testing the SSR with an external power supply, I verified that it also switches with 2V, the GPIO of the Blue Pill is perfectly capable of driving it directly both in voltage and current. I also tried to drive the buzzer directly but with bad results, the GPIO doesn't have enough current to drive it, you really need a mosfet.

There are no more significant difference between the hardware part of the projects. The software side of the Polihedron project, however, is very interesting. Also the Kp, Ki, Kd parameter he chose as default for the control loop are perfect for my system.

texasinstruments_PT78HT200 Series.pdf
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Step 2:

After mounting the control board, I was able to test the thermocouple, at least with the Nextion display simulation software (the physical display was delivered some time later). The probe suggested by Vulcaman (part of the kit with the MAX6675 module) is very good and accurate but with a response time that is too slow due to the mounting bolt that includes it. This behavior is not at all compatible with closed loop control for a oven that must follow a profile with rapidly changing ramps. The 1kW heater of the oven I choose is capable of following the required profile, the probe must also be able to do so.

So I decided to cut off the bolt case and directly expose the junction. Now, comparing it to another thermometer it is very similar, both in accuracy and response time.

YARO (Yet Another Reflow Oven) - Step #2
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Step 3:

After the actual display arrived, I repeated the tests with all the components. The main power switch is mounted on the back of the case. The control board is mounted on an aluminum plate which also acts as a heatsink for the SSR. After a certain period of intensive use there is only a small increase in temperature.

I chose the oven by comparing price, size and power. Many, many of them are available in the market.

I purchased it on the manufacturer's website thanks to a special offer during the Halloween period, but it is also available on Amazon.

The small size is useful for not taking up too much space in my laboratory. The 1kW heater is quite correct for a 10L volume, less power means not enough heat too quickly follow the desired profile. Do not choose the 600W, cheaper ones. With larger oven size, also increase the power to 1.5 or 2kW heater. The more the better, the closed loop PID controls the power actually needed to have the right temperature, modulating it. With a higher heater power it stays ON for less time but it is also able to react more quickly to any unexpected event. Just notice on the images that only at higher temperatures the profile is followed slightly slower than necessary. A little more power would be better.

I don't know if (much) more expensive oven are better thermally insulated. My oven does not have any insulation, as I have also seen on many other similar projects. Therefore, the outside of the case gets very hot, requiring a large distance from everything else. I decided to insulate the inner box from the outer case with the already linked wool rock. This is the only one I've found on line with a precise specification about the temperature it can withstand. On the other hand it releases many very annoying small pieces like dust, so I covered it with some aluminum foil.

Insulation also has the side effect of requiring less energy to maintain the correct temperature, making the most of the heater.