Kickstarter is at 13% of goal and climbing!

I just wanted to give a shout out and say thanks to everyone who’s contributed so far! There is still a ways to go so keep the support coming.

My Kickstarter Project

 

 

 

 

 

 

 

 

 

Temperature Controller Update

No video today but  I have been working on the code and have added some new features.

It is now possible to install a jumper across pins 19 and 20 on the I/O header (with the display removed) to enable a serial terminal mode. When the terminal mode is enabled the display and push buttons get turned off, and pins 10 and 11 on the header function as RX and TX lines. There is one small issue that I will talk about later in this post. Here is a quick screenshot:

Now what can the terminal mode do?  It’s still in the early stages but it already supports several commands. Currently the commands include reading the current temperature (“t”), setting desired temperature (“T”), reading the current temperature set point (“s”), reading the current PID constants (“p”,”i”,”d”), setting the constants (“P”,”I”,”D”), set display to Celsius (“C”), set display to Fahrenheit (“F”), and print all values (“v”). These commands are all working and allow using the controller without the LED display board.

The one letter commands were chosen for a couple reasons. The major reason is adding lots of strings to be displayed on screen takes up memory fast and I want the space free to include additional features in the future. The other reason is the one letter commands should be easy to remember and use.  With my use of the terminal so far this has been holding true. In the future the simple serial terminal could allow a nice PC based application to be written to allow tuning the temperature controller. That’s beyond the scope of the project right now, but the serial option now makes that possible.

I spent time this past week updating the board schematics and layout to fix a few minor issues and add a few things. Mostly, I added vias that would allow 3.3V, GND, and some of the more important signals to be tied into.  I also added a place for a small transistor to replace the opto-isolater on the board.  This will allow the Triac to be removed and an external relay to be switched. There is no space for the relay on the board, but I added solder points to make it easy to wire one off board. These changes will make it easier for myself and others to modify the board for other uses. One that was mentioned to me was controlling a mini-fridge to use in home brewing, especially lagering. This is something I would actually like to try since I do brew my own beer. I won’t have time to try this for a while, but the temperature controller will be a good fit for controlling the mini-fridge.

Coming up, I want to add functions and commands to set the temperature to Fahrenheit or Celsius, save the new settings to the internal EEPROM, and add code to the LED display to allow the variables to the changed and saved. Now that the code for the serial communication is working the other features should progress nicely.

Now the small issue I mentioned before with the serial communication, the PIC24F08KA101 the project is based on doesn’t have 5v tolerant inputs and there isn’t going to be voltage level shifting included on the board (no space for it currently). This means that the serial port on the PC side must use 3.3V signals to safely communicate with the temperature controller. Thankfully there are several options that make this easily possible.

The one I use and recommend is a Bus Pirate. The Bus Pirate is a small board that makes working with different serial communications protocols much easier. The price is very reasonable and maybe even cheaper than a “name brand” serial port adapter.  For the serial terminal I’m using the Bus Pirate in the USB-to-Serial bridge mode so it acts like a USB serial adapter.

Another option is a FT232 chip setup to work at 3.3V. Sparkfun has a breakout board that it set to work at 3.3 volt and would be perfect to use with the temperature controller. This is a good option if the board is going to be left inside a project. If the terminal is only going to be used to setup the controller the Bus Pirate mentioned above is a much more useful tool but either option will work just fine.

I also wanted to mention my kickstarter page again.  If you are interested in this project and would like to get your own board(s) please take a look.  With enough support I will able to do a production run of the boards and get them to someone like you.

Thanks for following the project and enjoy your day.

Karel

Toaster Oven to SMD Reflow Oven Conversion

Since I put up my kickstarter page, I have received a few emails asking about controlling a toaster oven using the laminator temperature control board. This is something I have been thinking about myself, so I decided to buy an oven and convert it into a SMD reflow oven.  If you decide to do this, do it at your own risk and make sure you, your family, and your friends know to never use it for food!!!

My only real criteria was that it had to be cheap. I bought one that was on sale at my local big box store (Fred Meyer in my case).  The exact model shouldn’t matter because the cheap ones are all pretty much built the same. For those that want to know, I got a Black and Decker “Toast-R-Oven”.  Here is what it looks like:

The first step was to take the side off and see what I was getting myself into. To take the cover off, I had to remove the feet from control side of the oven (right), and a couple of screws. A small annoyance was that the manufacturer decided to make one of the screws a Torx head (star driver). Once the screws were removed, the side panel opened on the bottom and lifted off. I needed to be careful because there are 2 metal tabs that hold the side panel in place on top and I didn’t want to bend them. With the side panel off, it was easy to see the wiring inside the toaster oven. Here is what it looks like:

The main power comes in on the lower right of the photo. The ground gets tied to the oven frame for safety. The neutral gets split with one side going to the power indicator on the front of the oven and the other going to the heating element return (lower right of photo behind the main power input).   The incoming “live” wire goes to the power switch/timer/bell on the left side of the photo. The output of the switch gets split with one part going to the “live” side of the indicator light, and the remaining wire going to the Function (broil/toast/bake) select switch. That switch determines which of the heating elements will be active. This oven has one element on top and one on the bottom.  The output of the function switch goes to the thermostat (top left of photo).

Since some experimentation is needed to get the reflow temperature dialed in just right, I decided it might be useful to have the function switch and timer/power switch still functional so I left them connected. The function switch will allow me to pick which heating elements get turned on. The timer/power switch will be nice to control the main power to the oven, while still having a stock easy to use interface.  All that is needed is to bypass the thermostat so the control board is in charge of maintaining the correct temperature and then wire the control board in between the power switch and function select switch.

The toaster oven I’m using is rated for 1200W (10Amps at 120V). Since the control board was originally designed to control up to 6Amps, I needed to do a couple small mods to beef it up; switch in a higher power triac (the BTA06 for a BTA20) and solder wire to the power traces so they could carry the higher current. Here is what it looks like:

I’m not sure the exact current rating after the mod but 10 amps won’t be a problem.  Next, I just need to wire in the controller and the toaster oven will have its new brain. For this trial run, the control board’s logic circuits are always powered, but the toaster ovens timer/power switch connects the triac to the heating elements for safety. I got lucky and the vents slats in the bottom of the oven were a perfect fit for the mounting holes I designed into the controller board. If this wasn’t the case, I could have easily drilled mounting holes in the toaster oven. Here’s another picture:

You can see the diode for measuring the temperature epoxied to the side of the oven(blue and white wires in the center of the picture). The diode isn’t rated for full use at the high temperatures needed for soldering, but will work great to show that controller works until I get the high temp thermistors I ordered. For now I will have to stay below about 150c.

I programmed the PIC microcontroller with the same code I used in the laminator, no changes were made. This means I have to use the display board to set the temperature, but for debugging this will be useful.  In the next rev of the code, I plan to add a feature so that the temperature can simply be set with a potentiometer so the display board won’t be needed.

Using a “Kill A Watt” to help me monitor the ovens power consumption, I began testing the modifications. By default, the controller’s set point is 50F, so the oven should be off. The Kill A Watt confirmed this with a reading of about 2 watts (a little power for the controller and a whole lot of noise). Next, I adjusted the set point to a few degrees above room temp and the control board increased the power to the heating elements as expected (and confirmed by the Kill A Watt). When I adjust the set point to several degrees above the measured temperature, the control board applies full power (about 1100 watts). Once the measured temperature nears the set point, the control board throttles back the power to minimize overshoot.

If you are interested in getting a set of boards please take a look at my Kickstarter project.

Stay tuned for further updates but in the mean time enjoy this somewhat long video of it in action:

 

A PIC Based Temperature Controller – Part 4

I have a basic user interface setup that allows the temperature to be set. Currently only the right 2 buttons are used, one for up temperature and the other for down temperature. When the laminator is turned on it shows the current roller temperature. Pressing the up/down button momentarily shows the set point, which is 50F at power up. This means the laminator is off by default. Holding up/down for a couple seconds starts the temperature changing in 5 degree increments every second. Releasing the button again shows the actual temperature of the roller.

I plan on adding code that will use the extra button to allow the set temp to be saved to the PICs internal EEprom and set again just by hitting the button momentarily. This will allow a commonly used temperature to be set quickly.  Also, the room temperature calibration will be entered by holding the 3rd button while powering on the laminator. The calibration will also be saved to EEprom, and will only need to be done once. After working with the the code, I also want to a feature that will allow the PID constants to be changed by entering a special mode. This will allow the board to be tuned for different uses without needing reprogram the PIC.

I have tried the laminator out at it works well. Here is a picture of the laminator heating up. Please ignore poor quality, I had to do a longer exposure because I was only getting one digit showing in the pictures. This is caused by the 3 digits being multiplexed and only a single digit being turned on at a time. The camera was fast enough to only show one digit on at a time.

I currently have the second sensor disabled, because the PID control loop does a good job heating up the laminator while preventing overshoot.  I will add the second senor as a fail safe that will turn off the laminator if the first sensor stops working for some reason. The laminator heats up to normal lamination temp of about 240F in less than 2 minutes. This is a nice improvement of the original 5 minutes or so it used to take, and is an added bonus of the modification.

I ran a blank board through a few times and the laminator only lost about 15 degrees on the first pass and recovered quickly.  After the 2nd pass the board was hot enough that I didn’t want to touch it.  This is a big improvement on the dozen or so passes it used to take. I need to see how hot the laminator will safely work. I have tried 260F for about an hour without any issues. If it can go a bit higher, a one pass toner transfer should be in sight. Worst case it will take 2 passes, which for me is very acceptable.

The display cutout was just done with a rotary tool, and while being a bit crude, works well. If I left the bit of plastic that would have gone between the display and buttons it almost would look stock.

Seeing there might be some interest in this project, I have set up a kickstarter page to try to get this into the hands of hackers and tinkerers like you. If you are interested, please feel free to check it out.

I hope to post a video of the laminator in action soon, but it’s currently apart as I was adding some features to the code.

A PIC based temperature controller for laminator – Part 2.

During my last post I started working on a custom temperature controller for a Scotch TL 901 Laminator.  I have finished the control PCB schematic and layout. Here is what the final PCB looks like.

Next, I removed the stock temp control PCB and did a test fit of the new board to make sure the mounting holes lined up, and there was enough clearance. Everything looked good so it was time to install the components on the board.  There is a lot of surface mount components used to save space, but the packages are all easy to work with. It just takes a bit of practice.

Now that the main controller board is built ,  its time to work on the PCB that will hold the three 7segment displays and 3 buttons that will make up the user interface.  Here is what I came up with:

On the left is the header to connect to the main control board, along the bottom there are 3 buttons for user input, and finally along the top the 3 seven segment displays.

The three 7 segment displays are a LSD3021 common anode unit.  Any common anode with the correct pin out should work. If it is not a red display, the current limiting resistors will need to be changed because of the different voltage drop for each color of led.  Make sure to keep the current around 10-15 mA maximum per LED. All the same segments are tied together, then go through a 100 Ohm resistor before going to the header which connects to a PIC Micro IO pin.  To control each display separately, a P channel MOSFET is used to the Common Anode connections for each digit. The MOSFETs are required because each digit will draw about 80mA when showing the number 8, this is a lot more than an IO pin can provide. The digits will be multiplexed inside an interrupt routine to provide the final 3 digit output.

The three buttons are normally open momentary push buttons from Electronic Goldmine, but any similar switch will work just fine. The pull up resistors are located on the main PCB instead of the display board. This is done in case the connecting cable gets broken or disconnected so the pull up resistors will still hold the button inputs in the default state.

Overall the display board is pretty simple and designed so it could be used in many other applications that need a very readable numerical display. It will work well with a 5v microcontroller as well, but current limiting resistors might need to be changed.

Here is what the blank display board looks like.

In the next post I will start to write code and try out the functionality of the circuit.