Another episode in the reflow controller story…

Here is yesterday’s graph again, but manually annotated this time:

Actually, I went ahead and extended the code to add those axis labels in there. I was concerned that they would overlap and distract from the graph data itself, but after seeing this… it clearly improves readability.

The trick is to get the PID control factors right, and these will be different for each setup. Right now, I just picked a couple of values which seem to be working ok on my particular grill. I’ve extended the JeeNode sketch to allow adjusting these values via a serial USB connection:

    <N> P       P factor (x1000)
    <N> I       I factor (x1000)
    <N> D       D factor (x1000)
    <N> L       I limit (x1000)

The PID calculation is:

    (Pfactor*Pval + Ifactor*Ival - Dfactor*Dval) / 1000

In other words, these factors are specified as a multiple of 0.001.

The result is brought into a range of 0..100. This in turn is used to determine when, how often, and how long to turn on the heater in the grill/oven/skillet.

The reflow profile parameters are also adjustable from the serial link:

    <N> o       ON temperature (°C), default 70
    <N> w       minimum time in WARMUP phase (sec), default 60
    <N> p       temperature at end of PREHEAT phase (°C), default 140
    <N> s       temperature at end of SOAK phase (°C), default 170
    <N> m       maximum REFLOW temperature (°C), default 250
    <N> r       minimum time in REFLOW phase (sec), default 15
    <N> c       temperature at end of COOL phase (°C), default 150
    <N> f       temperature at end of FINAL phase (°C), default 50

Once the FINAL phase ends, the JeeNode will power itself down.

A few more parameters:

    <N> l       lower calibration temperature limit (°C), default 40
    <N> u       upper calibration temperature limit (°C), default 120
    <N> d       stable duration (sec), default 5
    <N> t       stable trigger gap (°C), default 25
    <N> a       number of temperature averages to take, default 250

Some parameters for reporting, which happens once per second:

    <N> i       wireless node ID (sending disabled if 0), default 8
    <N> b       wireless frequency (4=433, 8=868, 9=915), default 8
    <N> g       wireless net group, default 5
    <N> e       enable (1) or disable (0) serial reports, default 0

And finally, the parameters which control the FS20 remote switch:

    <N> H       house code to use for FS20, default 4660
    <N> h       device ID to use for FS20, default 1

All PID factors and other parameters are stored in EEPROM, so they will remain in effect until changed.

To get a summary of all the current settings, type a question mark: “?”.

To reset all parameters to their “factory” defaults, type an exclamation mark: “!”.

The code for the “reflowTimer.pde” sketch is here The current code size is ≈ 14 Kb. I’ll probably be tweaking it a bit further in the coming days.

One thing I’d like to try adding to the current sketch is an easy way to self-calibrate and come up with a workable set of P/I/D factors, so that it can be used with a variety of electrical grills, toasters, skillets, ovens, barbecues, whatever – under the motto: if it can melt solder, we should try it!

The JeeMon script is here and is about 150 lines of code. If you save it as “application.tcl” next to JeeMon, it will automatically be picked up when JeeMon is launched. The code is still work-in-progress at this point: you will have to manually edit the “device” variable to refer to your attached JeeNode/JeeLink running RF12demo – you can also set it to a COM port (Windows) or tty device (Linux/Mac). Likewise, the “nodeID” variable should be set to match the current setting in the Reflow Timer sketch (“i” parameter):

    variable device   usb-A900ad5m    ;# which JeeNode/JeeLink to attach to
    variable nodeID   8               ;# which node ID to listen to

The frequency band + netgroup of the JeeNode/JeeLink are assumed to have been previously set in RF12demo.

Note that the script is an optional GUI front-end – you can launch it anytime, or you can ignore this whole JeeMon thing, since the sketch does not depend on it. It’ll drive the reflow process with or without the GUI.

If you try this out, or have suggestions about how to improve things, please let me know.

Update – I’ve adjusted the info above to match the latest code changes.

This is part 7 of my reflow controller series.

Reflow soldering is a pretty simple process. Take a PCB, add solder paste, place components, and then let the whole thing go through a controlled reflow termperature profile. As I’ve described before.

In my (limited) experience, these temperature profiles are not nearly as critical as one might expect. Just preheat the thing while staying under the melting point of solder, then ramp up and keep it all well over the melting point for a while. Not too high and not too long, so nothing gets damaged. Then let it cool down. That’s basically it.

I’m going to use the following profile to start with:

• do nothing for 10 seconds
• heat up to 140°C
• stay there for at least 30 seconds
• heat up to 170°C
• stay there for another 20 seconds
• heat up to 250°C
• stay there for 15 seconds
• turn off and open up the grill for fast cool down
• the finished board can be removed when under 150°C or so

In code:

I’m staying a bit longer at the high temperature because my grill is a bit uneven in its temperature distribution. I want the cooler spots to work properly as well. Hopefully that won’t damage anything.

So how do you go from a thermostat to a reflow controller? Simple: implement the profile. I added a RunProfile proc, which keeps calling itself over and over again, so it behaves like a background process. Its task is to adjust the target variable over time to match the requested reflow profile. When a step has been completed, it will be removed from the front of the profile list:

RunProfile is called in start, right after calling InitPlot.

Ok, let’s try it:

Hey, this is starting to look like something!

I changed the colors a bit and am now also plotting the target temperature for reference.

Latest source code available here.

But all is not well. While trying this out, I noticed that the current setup hangs once in a while. No more incoming data, so the plot and the control stops. I suspect that there’s an occasional conflict between sending out OOK commands and handling incoming packets – perhaps a bug in RF12demo. I worked around this by omitting all the redundant OOK commands.

There was also another case where the last temperature target was set, but the heater wouldn’t get turned on, i.e. HeaterControl returning 0.

So… progress, but not finished yet!

This is part 6 of my reflow controller series. Let’s see if we can get the reflow grill to a stable 150°C.

It’s not trivial: this grill has a slow startup time and a very noticeable lag in its response curve. Turning on the grill and turning it off at 150° is not the way to do it, since the stored heat will lead to a huge overshoot.

The proper way to do this is to use a PID control algorithm. PID stands for Proportional Integral Derivative. It’ll be interesting to try that, but first I want to try something simpler (actually, it is still PID, but just P and D).

The idea is to try and predict where the temperature will end up when we turn the heater off. I’ve got two relevant pieces of information for my particular grill, obtained from the last few trials:

• The grill will heat up at about 2.5°C/sec once it gets up to speed.
• When turned off at that rate, it appears to overshoot by about 40°.

Let’s try something easy first. Let’s find out what the grill does when turned off at 110°. I’ve added this line to the GotData proc to do so automatically:

if {$value >= 110} { set heat 0 }

Result:

Not bad – still some overshoot, so I’m going to assume an overshoot of 50° from now on. BTW, this is not the same as keeping the oven at a preset temperature, but it’s a start. In fact… I’m going to keep this line as a permanent safety valve:

if {$value >= 265} { set heat 0 }

It’s not essential, since the grill has a mechanical temperature cut-off as well, but that way I can be sure that this code will never try to push its heater beyond 265°C. It would have avoided yesterday’s runaway failure.

To improve on this, let’s assume that the overshoot is proportional to the heat-up rate. So if we turn off the heater while it’s heating up at 1.25°C/sec, it will overshoot by 25° – it seems plausible, since that probably means the heater hasn’t been on that long yet, so there is less “stored excess heat” in the system.

Next thing to do is to track the rate of change and base heater decisions on that. I’ve added a new HeaterControl proc which decides what to do for a given target temperature:

Note that heater control is simply a matter of setting the heat variable. It controls both the remote switch and the GUI checkbox, courtesy of Tcl’s built-in variable tracing facilities. This does the actual control, in GotData:

set heat [HeaterControl $value $lastv $x $lastx]

And in the start proc, this extra code will get the ball rolling:

variable target 0
after 10000 set [namespace which -var target] 150

IOW, after 10 seconds, JeeMon will attempt to maintain the grill temperature at 150°C. Let’s try it:

Woohoo, it works! A thermostat!

The “application.tcl” source code is available here. Next step is to add a reflow temperature profile.

This is part 5 of my reflow controller series.

Today, I’d like to be able to remotely turn the grill on and off. To avoid having to deal directly with high voltages (220V is scary!), I’m going to use an RF controlled switch – i.e. this FS20 module:

It’s perfect here, because it operates @ 868 MHz and can be controlled directly from a JeeLink or JeeNode, and because it has an on/off button right on the unit itself (unlike these). Which is great as emergency stop – we’re going to play with serious levels of electricity, current, and heat after all.

As it so happens, the RF12demo sketch I’ve been using to receive packets from the thermocouple node also supports sending FS20 commands out of the box.

So all that’s needed is to extend the GUI a bit with a control element, and hooking that up to send the proper FS20 command out.

This requires a few extra lines in the initPlot proc:

variable heat
pack [checkbutton .h -text Heater -variable [namespace which -var heat]]
trace add variable heat write [namespace which HeatChange]

And a proc called HeatChange, for which I’ll use a bit of test code for now:

proc HeatChange {args} {
  variable heat
  puts "heat = $heat"
}

The result is a window with an extra checkbox at the bottom:

Clicking that button simply generates some test output:

heat = 1
heat = 0
heat = 1
heat = 0

Great. The GUI side is working. Here’s an updated version of HeatChange which actually sends out the proper FS20 commands:

proc HeatChange {} {
  variables heat conn
  if {$heat} {
    $conn send 54,32,1,17f
  } else {
    $conn send 54,32,1,0f
  }
}

The first 3 values are the house code and address bytes. They can be anything, because FS20 modules are configured by putting them in a special listening mode (press the button until the LED starts blinking). The next RF command sent to them will then be remembered, so that it will respond to that specific code from then on. Code 17 means ON, code 0 is OFF – that’s part of the standard FS20 protocol (see this German info page). The trailing “f” tells RF12demo to send everything out as an FS20 command.

IOW, to respond to these RF signals, put the FS20 unit in that special mode and then send one of the above commands by clicking on the checkbox in the GUI. You should now be able to manually control the remote switch.

Note: make sure you have the latest RF12demo. A nasty OOK bug was fixed a few days ago. If your JeeLink hangs: unplug, reconnect, then upload the latest code.

One more thing I’d like to do is include the heater status in the plot. That requires a few more changes. Here’s the latest “application.tcl” (I’ve collapsed the start and HeatChange code, since they are the same as before):

Let’s try this new setup, i.e. measuring and controlling 100% by wireless.

What I wanted to do is hook it up to my Ersa I-Con Nano temperature-controlled soldering station (with the soldering tip removed), because that would have been a great demo of how real temperature control works:

Unfortunately, that didn’t work – and drove home that there’s a real risk of fire involved in these experiments. Here’s what happened:

The temperature shot up to 450°C in seconds! – I think there’s a sensor in the very tip of the iron, and it wasn’t touching anything, so this heater went full blast – charring the thermocouple insulation on its way up. I switched the iron off manually, and then everything coooled off.

Second try, this time replicating yesterday’s setup:

Perfect. A step pulse and the response curve (grill was opened @ 175°C, like yesterday).

Warning: if you try these experiments, make sure you unplug your oven / grill / whatever when you’re done. Starting a fire while you’re tinkering with something else, or out of the house, or asleep is not a good idea…

Tomorrow, I’m going to create a feedback-control loop.

This is part 4 of my reflow controller series.

Data is coming in over the serial USB connection. Quick, let’s visualize it!

There are two ways to do this: with some external tool such as Excel, or with the GUI facilities built into JeeMon.

Let’s do Excel first, because it requires less coding. Change yesterday’s “application.tcl” example to this:

proc start {} {
  set conn [Serial connect usb-A900adav 57600]
  oo::objdefine $conn forward onReceive [namespace which GotData]

  variable fd [open logfile.csv w]
  chan configure $fd -buffering line
  puts $fd "time,temperature"

  vwait forever
}

proc GotData {msg} {
  variable fd
  if {[Serial cmdParser $msg OK -node id -int1 temp]} {
    puts $fd "[Log now],$temp"
  }
}

The cmdParser function in Serial helps with decoding the “OK …” lines. It takes type arguments and variable names. In this case the node id header and an integer, to be stored in a variable called temp. The “-int1” notation means: treat the int as having one decimal, i.e. convert 123 to 12.3, etc.

Run JeeMon and it will create a “logfile.csv” file with readings (in “Comma Separated Values” format). You may have to stop JeeMon before you can open the logfile with another application.

Using “Numbers”, a Mac OS X application similar to Excel, this is what I get:

You can see the sensor at room temperature, heating up as I touched the thermocouple, and then cooling off again gradually.

The other approach is to create the plot with Tk, the GUI toolkit which is built into JeeMon, as I did with the OOK Scope. This is more work, but you get a plot which updates in real time.

So now let’s make a graph. I turned the grill on until it reached about 175°C, then let it overshoot and cool back down to 175°C again, and then I opened the lid. This is the result over a period of some 8 minutes:

Looks like this little grill will overshoot by some 40°C, and that it can heat up about 2.5°C per second. It’s only 700 Watt, which probably explains it. Should be fine for reflow, though.

This is the code I used, i.e. “application.tcl” (source here):

All this is standard Tcl/Tk code, as documented here if you want to explore how it works. With some elbow grease, I hope to add such basic plotting facilities to JeeMon as utility code, hiding most of the distracting details.

Tomorrow, I’m going to add remote switching to control the oven.

This is part 3 of my reflow controller series. I’ve got a remote node sending out temperature readings once a second, and now I want to do something with that data.

First step is simply to get it into JeeMon and display values as they come in.

Warning: JeeMon is not Emacs, Eclipse, or Processing. For several reasons:

• JeeMon is portable across a far wider range of platforms. The core also works on tiny embedded Linux boards such as this one, for example.
• I want a system which can be wrapped up, shipped, and used elsewhere without installation hassles – even cross-platform. JeeMon can do that.
• I prefer to use the same editing environment for everything I do because I work with lots of different environments, so I use “TextMate” on Mac and fall back to “vi” on Linux.
• JeeMon can be grown into a “big” system, but it doesn’t need to. It can also be used as bridge for numerous other tools.
• There’s a lot to like about big environments which take care of everything, but I prefer lower-level tools which let me get under the hood and tinker.

Does that make JeeMon primitive? I don’t think so. Infancy: yes. Limited scope: yes (so far). One-man activity: yes (so far). Perfect: nope (nothing ever is). Fit for its intended purpose: you bet!

All good things come in three, so to work with JeeMon, you need three things:

• The JeeMon runtime, a single executable file.
• A programmer’s editor. Pick your favorite. Get a good one. It’ll change your life, as developer.
• Willingness to figure out how to glue things together using the Tcl programming language.

Let’s get started.

1. Set up the tools

There are JeeMon binaries for Windows, Mac OS X, and Linux as ZIP files, 2..3 Mb each:

• Windows: 32-bit, 64-bit
• Mac OS X: 32-bit (Universal)
• Linux: 32-bit, 64-bit

Download the one you need, unpack, and you should end up with an executable called “JeeMon”. Feel free to rename it to “jeemon” (lowercase) or even “jm”. These files are 100% open source, but they’ve been wrapped up into single-file executables to get going fast. See the JeeMon page for more background info on the technology used inside JeeMon.

As for which programmer’s editor to use, you’ve probably already got a preference. It doesn’t matter what it is – stick with it and learn it well, is all I can say. A good editor lets you find references and definitions, colorize your source code, compare file versions, lookup documentation, create boilerplate templates, interface with a version control system, and much much more.

2. Get organized

This is going to be a moving target. I’m still exploring the best way to manage code and data, so that it is easy to use in the editor, in the Arduino IDE, and with JeeMon.

The Arduino IDE already sort of imposes a structure to use for its libraries and sketches. Fine.

We just need a good place for JeeMon. I suggest creating a new folder called “JeeMon”, right next to your “Arduino” sketches folder. On my Mac, that happens to be the Documents folder. This is where the above JeeMon executable should be placed.

Here’s a mock-up of the folder structure I have, when following the above guidelines:

It should be fairly similar on Windows and Linux, I expect.

3. Tie everything together

This is where the real work starts. We need to tell JeeMon how to hook up to the JeeLink, and what to do with incoming packets once connected.

Everything in JeeMon is always driven from a file called “application.tcl”. For this first trial, we can just create that file next to the JeeMon executable itself. Create a file called “application.tcl” with the following contents:

proc start {} {
    array set ports [SysDep listSerialPorts]
    parray ports
    vwait forever
}

In prose: call the listSerialPorts function in the SysDep module, and store the results in an array called ports. Then print that array. Then just stop and wait (but don’t exit, because then the output would be gone too).

In JeeMon, modules are called “rigs” btw – SysDep is a built-in rig. The above “application.tcl” file is also a rig. Once initialized, the system executes “application start” as its very last step. Which is how the “start” procedure in the above “application.tcl” file gets control. There’s no magic and very little syntax. Just some conventions.

Launch JeeMon. Sample output here, with three JeeNodes / JeeLinks hooked up:

ports(usb-A8007UsI) = /dev/tty.usbserial-A8007UsI
ports(usb-A900ad5m) = /dev/tty.usbserial-A900ad5m
ports(usb-A900adav) = /dev/tty.usbserial-A900adav

Your output will be different. The info you need to extract from the output is the connection name of your JeeLink. In my case it is “usb-A900adav”, so that’s what I’ll use in the following examples.

Stop JeeMon.

Replace the contents of “application.tcl” with the following code, but use the name of your interface in that second line, of course:

proc start {} {
    Serial connect usb-A900adav 57600
    vwait forever
}

In prose: call connect in the Serial rig, then wait forever. Communication takes place in the background.

When you start JeeMon again, you should see some output similar to this:

22:04:30.328        . (adav) [RF12demo] _ i31 g6 @ 868 MHz 
22:04:30.342        . (adav) DF I 42 4
22:04:30.343        . (adav) Available commands:
[...]

That’s output from the JeeLink. When the thermocouple node is turned on, you should see its packets being reported. Sample output:

22:04:34.348        . (adav) OK 33 209 0
22:04:34.350        . (adav)  -> ack
22:04:35.346        . (adav) OK 33 212 0
22:04:35.348        . (adav)  -> ack
22:04:36.344        . (adav) OK 33 206 0
22:04:36.346        . (adav)  -> ack
22:04:37.341        . (adav) OK 33 209 0
22:04:37.343        . (adav)  -> ack

Not much to write home about. But now you’ve got all the pieces in place to start doing more interesting stuff. GUI, networking, webserver, database, it’s all there in JeeMon, waiting to be activated and combined as needed.

There will be some minor differences between Windows, Mac OS X, and Linux, but not much really. If you’re following along and things don’t work as expected, please let me know. I’ll be happy to adjust these notes to cover as many possible details as needed to get going.

Let’s get back to the reflow side of things. We need to figure out how our thermocouple and our oven behave, and after that we need to find a way to control the oven temperature. No worries – one step at a time.

Tomorrow, I’ll set up a temperature graph. Two, in fact.

Note – as of mid 2011, this info is no longer valid. JeeMon has evolved to version 1.5.