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What is Reflow Oven Controller

( 7 Votes )

The board is Shield for Arduino. It has 2x16 blue display with white backlight and option for contrast adjustment. It has and two relays - 25A, with them you can control up to 4500 Watts for each. Thеre is three control buttons, 2 LEDs showing satus of the process of soldering and audible buzzer.

   

 What is this?

…will start from the far little....

As we all know electronics has become an integral part of our lives. In an effort to miniaturized electronic devices, electronic components makers have created SMD versions of almost every electronic item. But the parallel with this need to resort to other means of soldering, far different from our notorious way Soldering - Soldering with hot-air. Elements were created with very little distance between the legs where one of the soldering tip is too large for successful soldering as elements with socket 0604 are even harder to hold with tweezers and need to be handled with vacuum pumps as to take it use medical needle at the top. The real difficulty comes when you have to solder such small parts one by one. In one of my projects of the Interactive LED Flower having to solder over 350 miniature resistors of this type including even other types of SMD components. So we had to look for the easy option and the quality soldering.

…now essentially...

Reflow Oven Comtroller is a device that is shield for Aruduino. If you are not familiar with what Arduino can be found in Wikipedia a little more about his powers. http://en.wikipedia.org/wiki/Arduino

In a few words, Arduino is uniquely simple device that has a powerful processor and very analog and digital - inputs and outputs. It can be USB powered with 5V or can use adapter with output voltage of 12 volts. Our product, is planned corresponding to 12-volt power adapter, although that would work with power from USB. Software that  program Arduino has a wide variety of libraries and may cause the device to work with your requirements without significant knowledge of electronics and programming. You need a little basic knowledge of C programming. So far, for Arduino has developed many Shields and as I mentioned earlier with just a few lines of code you can make it run displays to monitor sensors and other peripherals. Offered by me product is a device that is placed on a rake Arduino Uno and I have proposed calibration software and a slightly your discretion can make an oven for SMD components.

 

Reflow Oven Controller - Board (Powered by 12 Volts adapter)

 

Reflow Oven Controller - Board (Powerwd by PC's USB)

 

Reflow Oven Controller - Demo Oven (Prototype)

 

How happened soldering in Reflow Oven Controller?

SMD soldering is done by solder different from our knowledge so far. It's name is (solder paste) liquid that is a mixture of flux and solder balls of a certain size. There are various types depending on our goals, but even those sold in Chinese sites such as www.dealextreme.com you can get surprisingly good results. This type solder paste applied with stencil that you can order the company that produces your boards.

 

 

The stensilat iis foil with cuted holes only where there will be soldering the components. Solder paste is applied with a spatula and solder paste pass only through the holes in the bottom so the inserted board is covered with solder paste only contact sites where we will solder elemets later. Then carefully place the items and put in the oven for the actual soldering process.

 

Why is needed calibration of the oven?

To achieve good soldering, solder paste have to go through several stages. Below is shown a diagram of how solder psate heating to achieve the best results when soldering. I personally use a small toaster which put four wire 550 watts, 2200 watts total. My oven has a factory built-in fan for better heat transfer inside the oven. Your oven may have other specifications and have different power the, threfore have to do again-calibration to set up parameters of the software to work optimally in your case. Keep in mind that too much oven has more inertia / slowly heated and slowly cooled / or power different from mine also would require changing the parameters of the software parameters that is work well for me. I can not guarantee what the minimum power at which you achieve results, but I think that with a little experience and enthusiasm to achieve the required results.

Diagram of optimum temperature change soldering liquid solder paste

 

For optimal results it is necessary to pass soldering through four stages of temperature which is set in the Arduino software.

  • First stage – Pre-heating increasing the temperature from ambient to about 150 degrees. The rate of increase should not be faster than 2.5 degrees per second.
  • Secind stage – Soak from 150 to 180 degrees. Process should not take more than 2-3 minutes.
  • Third stage – Reflow the temperature should be increased sharply to 240 degrees and then cooled to 200. This process should be done in about 1 minute.
  • Fourth stage – Cool oven must be cooled to room temperature. This process should be very fast to not form a cold solder joints.

Subtleties in calibration and conclusions of experiments

  • Even if you do not stick perfectly under the above conditions, you can achieve the desired results. For example, in my case, the process of preparation (Soak) does not reach 180 degrees and stays around 150 to 155 in about 2 minutes.
  • In Reflow solder past melt 208 degrees, and I do not have a temperature of 240 degrees.
  • Upon cooling I have to open the door slightly to speed up the oven cooling to room temperature.
  • After cooling the oven process can not be restarted if the temperature is low and below 50 degrees. This temperature can be change in the source code # define TEMPERATURE_ROOM 50.

 

Software and how it works

I share the software that achieves surprisingly good results. I guess you will not have a drastic change in the the parameters in your configuration when calibrating. If it is required i advise you to first change the PID parameters from the source code.

// ******************* PID PARAMETERS *******************

// ***** PRE-HEAT STAGE *****

#define PID_KP_PREHEAT 80

#define PID_KI_PREHEAT 0.03

#define PID_KD_PREHEAT 20

// ***** SOAKING STAGE *****

#define PID_KP_SOAK 180

#define PID_KI_SOAK 0.5

#define PID_KD_SOAK 60

// ***** REFLOW STAGE *****

#define PID_KP_REFLOW 150

#define PID_KI_REFLOW 0.1

#define PID_KD_REFLOW 25

The software monitors the temperature of termocouple (Type K) and uses an algorithm PID (proportional integral derivative) calculation and correction of errors from the difference in current status and parameters that must be achieved. PID algorithm is very complicated to explain, and if you wish to explore in more detail can be found in Wikipedia http://en.wikipedia.org/wiki/PID_controller, note that to set the software for your oven does not have to probe PID algorithm. I'll explain simple techniques you can achieve results that you seek. 

PID consists of three variables. I suggest you first change the parameter Kp to get a long enough period of inclusion of wire to reach the correct temperature. If the power is too large and the temperature rises more than aim, change the second parameter Ki for you to have the correct values. With the third parameter Kd make fine error correction from the previous two parameters. Be patient calibration is very delicate moment, but then your patience has paid off.

 

Software needed for program Arduino

Software which is needed to program Arduino memory, you can download from the official website of the manufacturer.

The project attached below is tried and tested with Arduino 1.0.1, but it is assumed that in the future there is no reason not to work with the new versions of the software, unless drastic changes are made by the manufacturer in the future.

http://arduino.cc/hu/Main/Software

The source code of the program with set parameters which work optimally with configuration of my the oven:

Reflow_Oven_Controller_V2.zip

Libraries that are needed to successfully compile the source code are:

PID_v1.zip

MAX6675.zip

PID_AutoTune_v0.zip

LiquidCrystal.zip

The password for all archives article: www.kukata86.com

They are copied in subdirectory (folder) librares Arduino software.

Ready 1.0.1 Arduino archive (all included), source code and required libraries can be downloaded from here:

Arduino-1.0.1_include_files.zip

The password for all archives article: www.kukata86.com

Source code has the option DEBUG, which if set to 1 will enable the display data to be sent to PC via the serial port to box program the Arduino. So to measure the temperature changes over time. This would make it easier for your calibration. Be sure to set the correct speed of acceptance of the same data as in the source code, which is 57600 bps.

 

 

What has the Reflow Oven Controller?

 

  • 2x16 Line display - which displays the current temperature and the stage of the overall process of soldering.
  • 3 buttons - First restarts Arduino, the second - on/off the process of soldering, the third is not used yet and is left for further software upgrades.
  • 2 LEDs - Green blinks when soldering process is started, the red shows the next stage of the process.
  • 1 Audible Buzzer - alarm at the beginning, end, and transition between stages of the processes.
  • 2 SSR* relays - control fan and coils. Relays withstand 25A = 4500 watts maximum for each
  • 1 input - for thermocouple type "K" 

SSR relay is relay with electronic control, without mechanical contact. By using this relay avoid unpleasant clicking when the relay is have to be switched on and off to control the coils and adjust the proper temperature. The relays are controlled from 3 to 36 volts and so we can easily manage 220 volt circuit from 5 volt output of the Arduino. Space is available for mounting the heatsink on the bottom side of the board under the relays if you need to use the oven  often and on the verge of relays.

 

What thermocouple to use? 

It is nessesary to use a thermocouple type "K". The most popular is from 0-400 degrees they are doing a great job for the purpose. although there are thermocouples with a wide temperature range, in our case it is not necessary. Our maximum temperature we seek in the oven is 240 degrees. I advise you to spend a metal casing (if any) of the thermocouple so that it can react quickly to changes in temperature in the oven. If you wrong the polarity thermocouple will not fail the controller, but the temperature rise in the oven unit will record lower temperatures and similarly vice versa.

 

How to connect the board

Shield connects to an Arduino board using pins putted on the back side. Basically Arduino is designed to be non-standard pitch railing on both pins. Thus the potential to prevent wrong (back) put the plugin in it. However look at the photos in the gallery where exactly is shown how to cpnnect the board to the Arduino. Pins that are used are marked in red, others in two pieces on the left side of the picture are left unused.

After connecting the Controller and Arduino remains to attach to manage your oven. This is is done by successful connect serial heating element and fan (if any) with SSR relays. (If you do not have a fan in the oven you can do to SSR FAN to manage  bulb inside the oven or leave it unusable. If you change the source code of your choice, you make it work for any other purpose for whatever you think of). Power the oven with 220/110 voltage and  power Arduino with 12 volts stabilized adapter. The Shield itself is powered by Arduino output pins, ie do not need a separate power supply for it.

Assembling the board

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