No, this post is not about Megatron looking for energon cubes. We just love labeling all our tools and machines with characters from the show we heart when we were young. Alright, finally there’s some progress on the reflow oven controller. I know many of you guys are asking when they’ll be available, I hope the waiting is going to be over pretty soon! 🙂
While working on the reflow oven controller firmware, we came across some sample codes from Adafruit (Thanks LadyAda!) posted on GitHub (GitHub rocks!). We grab the codes and make some changes on it to suite our hardware setup and the results are pretty amazing. The implementation of the PID control is pretty straight forward and simple to understand. But, it would be advisable to go through this article to get a better understanding especially on the theoretical part.
We are using a 10 A SSR from Crydom which can be controlled from a 3-32 VDC line (just nice for Arduino) to control the oven. The following image shows our setup for the SSR interface with the AC high voltage (be extra careful when dealing with high voltage, please make sure you know what you are dealing with). I would not advise using this setup for safety reason as we tripped the whole power line supply when we accidentally causes some leak from either the live or neutral line to earth!
Upon uploading the example codes onto the Arduino Uno, we hook everything up together with a type K thermocouple stuffed inside the oven. The serial-USB of Uno is connected to the PC with a serial terminal program to log the temperature curve for analysis purposes.
The sample codes allows a start of reflow process to be triggered by a push button and a valid thermocouple wire must be attached in order for the process to be executed. Before starting the reflow process, we push the temperature and timer knob of the oven to maximum.
At each stage of the reflow stage, the stage name, time in seconds and current temperature in the oven will be displayed on the LCD. At the same time, the data will also be sent to the PC over the serial line. The data is useful for reflow curve analysis to perform further tweaking. So, time for some baking now. 🙂
Once the reflow process is completed, the temperature in the oven drops down to room temperature. We slowly open the oven door to help the cooling down process. Data collected from the serial is plotted to check the outcome of the reflow process. This is a 1st run without making any tweaks to most of the parameters used in the code. We are pretty happy with the result and we can’t wait to bake some real PCB. We just ran out solder paste as 2 solder paste jars in our storage are way too hard to be used. It’s time to get some new solder paste together with a mini cooler storage.
Judging from the reflow curve, we didn’t achieve the peak temperature for lead-free reflow process. The sample code comes with a default 232 °C peak reflow temperature which probably more suitable for leaded reflow process. Some adjustment is required on few parameters and the application level codes. We’ll post it up once it’s completed. We are attaching the schematic for the reflow oven controller for your reference.
At time of writing, we have completed making changes to the PCB design for the final revision. This includes some pin swapping for easier firmware implementation and rearrangement of components especially the push button in order for it to be more accessible for users. We hope everything will be ready by early next month and the lead time of components doesn’t change. Take care.