Kiln temp and humidity logger using the Raspberry Pi platform

[Crusarius]

So true. Now I need a metal detector. the spalted maple was a yard tree and already took out 2 blades.

[btulloh]

Maybe I should have said every problem is just and opportunity .  . .  to spend money.

The Woodwizard metal detector works ok and is not too expensive.  There have been some good discussions on here about detectors.


Edit:  LumberWizard   NOT Woodwizard.

[btulloh]

Well the wick is on the way from Nyle.  In the meantime I found a library of psychrometric functions already written in several languages including c++ on github.  Got it incorporated and checked out and all is fine.  Sure saved me a lot of work.  I had already written several functions for temp, rh, and dew point conversion which were working fine, but now I have ALL the needed functions.  Sort of makes up for all the wasted time chasing shoe laces and wicks.

PAW - thanks again for steering me to Nyle.  Wicks are on the way.

BTW - in my quest yesterday for wicks and shoe laces, I bought some 1/2" colman lantern wicks, which fit the sensor perfectly.  I was skeptical about them working correctly, (which was validated by Dr. Gene's post on WB's), but I installed one anyway, because - well - why not.  It didn't take up water very fast compared to other materials and appeared to be a complete bust yesterday evening.  This morning it seemed to get saturated pretty well and today I'm getting a WB reading that is 11-12 degr. below the dry bulb right next to it.  I have no reason to believe that to be accurate, but it's interesting that is sort of working.  Not that "sort of working" is very useful, but it gives me something to run through my new functions and test the math.

[GeneWengert-WoodDoc]

In the fall meeting of the Southeast Dry Kiln Club in NC or VA, I believe there will be a presentation on measuring the MC in a kiln during drying using pins.  

This subject will also be in an article in Sawmill & Woodlot magazine, as soon as I write it.  It will be discussing the Delmhorst two-pin-depth system and results with white oak being dried green.  We got it working pretty good, indeed.  But it is tricky.

For resistance vs MC for many species, see Table 1 in
https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr06.pdf

[boardmaker]

Somehow I overlooked this thread.

The only thing I have ever done  with a Raspberry Pi is run an emulator so my son can play video games...

In my professional life, I am in charge of all the automation in a large sawmill.  I have redone our dry kiln controls.  All PLC based.  I always thought of adding or playing with some load cells.  I've never actually seen another company use them successfully.  I have noticed that some dry kiln manufacturers do offer them. So with all the advancements in automation over the last 20 years, I'm sure we can figure this out.

Anyone have a recommendation for a load cell to buy?  I'd be willing to purchase and guinea pig it.

[btulloh]

I've never actually seen another company use them successfully.

That seemed to be the conclusion when this came up earlier in this thread.  It doesn't preclude future success though.  I would think it comes down to cost/benefit more so than technology.  At some point that could change.  Maybe that's now.  I don't have any direct experience with load cells, but I'd be willing to bet someone on here does.  I would be interested in following your progress. 

[GeneWengert-WoodDoc]

When drying hardwoods, we want the MC of the wettest pieces and not the average for a load.  So, we need to weigh individual samples.  I have yet to see a small load cell that can tolerate kiln conditions and not drift or lose calibration.  I built a load cell kiln back in 1986.  I saw one load cell kiln that had the cells on the outside with a wire running into the kiln and a sample was hung from the wire.

[boardmaker]

Gene,

I've heard similar feedback.  I don't really like the idea of hanging by wire because that would mean your sample would be hanging in the back of the kiln.  I want mine in the pile.

I know SII offers individual sample load cell weighing, at least their website still shows them offered.  I haven't heard any feedback from anyone yet though.  I'm considering just calling them and seeing what they have to say.

[Crusarius]

A series of 4 load cells in the floor with rubber seal on top to isolate them from the interior of the kiln would be ideal. 

Be very simple to write a formula in excel to start with baseline readings and then calculate MC based on weight loss. All you would need is weight of water and starting weight of stack. it will not give you MC for each board but will give you an average that will probably be close enough to determine if you can remove the stack or not.

Final check would still be done using moisture meter or some other measuring method. But the weight would at least make it so you did not have to go into the kiln all the time.

[btulloh]

Boardmaker, I think it would get more feedback if you started a new thread on this subject.  I don't mind getting off on a tangent here in this thread, but it would probably draw more attention from some of the people on the FF who have experience in this area if it was referenced in the heading.  Not trying to run you away, just thinking it might get some more input as a separate thread. 

Glad you're joining the discussion.  Sounds like you've got a of direct experience.  I'm just a hobbyist unconstrained by excess knowledge.  My career was far, far away from sawing and processing lumber.

[No_Dude]

While I don't have any Pi experience, or Kiln experience for that matter, I did deal with some robotics code that was based off C++ I think it was ??? Anyway, I'm starting as an engineering student, so I'll be with some smart cats, hopefully I'll be able to hop in with yall on this. I imagine we could probably get a solar kiln set up on campus. For the sake of bringing everyone up to speed and centralizing what stage you are at, I think it would be a good idea to set up a road map on where we are and where to go. 

[JoshNZ]

@btulloh whatever happened to this, are you elegantly driving your kiln from your cellphone while sitting in your arm chair?

I'm developing the same thing now, seems I've pretty well arrived at where this thread seems to have ended. I was going to use the node-red platform to make a web based dashboard to monitor and interface with.

[btulloh]

@btulloh whatever happened to this, are you elegantly driving your kiln from your cellphone while sitting in your arm chair?

I'm developing the same thing now, seems I've pretty well arrived at where this thread seems to have ended. I was going to use the node-red platform to make a web based dashboard to monitor and interface with.

Haha. My next project will give me the ability to stack lumber while sitting in my arm chair.  :D  A bit more complicated but highly desirable.

I did this project more out of curiosity about what was occurring in the solar kiln than any need for control. The solar kiln doesn't need much control beyond adjusting the vents as the load loses moisture and turning the fans on and off as needed.  Once you get sort of used to the solar kiln dynamics it's not complicated to run. That's why Yellowhammer calls them an easy-bake oven. It is possible to over dry if you don't pay attention as you approach the desired mc though.

I learned a lot about the kiln dynamics from the data I collected, but none of that is required for achieving good results. It also filled up some free time in the dead of winter when it was more pleasant in the house than outside.

Node Red should be the perfect platform for monitoring your sensors and building a web based graphical display. Sounds like you're well on the way.  I did a limited web based display using Thingspeak as a place to push data and display real time results.  Easy way to get something up on the web but limited ability to design the best gui.  My main objective was to store the data in a csv file then retrieve and analyze it later.

What are you using for humidity sensors?  That can be tricky as the easy choices are not robust and are not well suited to the environment. There are industrial sensors that can handle the kiln environment but I didn't go there. I ended up doing a wb/db arrangement that worked pretty well as long as I serviced the wb tank and wick regularly. All in all this project was more to satisfy my intellectual curiosity than to manage the solar kiln. Really no driving required, but it did give me a good way to automate the fans or control them remotely from my arm chair.  If I had added a way to control the vents remotely it would have been pretty slick, but that was a lot more complex and the weather got better long before I got to that point.  

Maybe this winter I'll work on that remote controlled lumber stacking machine i can run from my arm chair.

I'll be interested to see how your kiln control turns out.

[JoshNZ]

I'll keep you posted with how I go. I was going to get the first load running with a rudimentary tstat and hstat and then maybe ghost it with the rpi but I think I'm just going to punch straight into it first round, all in.

Im basically after a dashboard that has switches and status indicators of 4 things, the compressor, heater, compressor/heater fans, and circulation fans. I'll probably add vents later too but maybe not at first.
Then I want to display the RH and temperature, and I want to graph them both plus the time the compressor and heater will have been on. The heater more out of interest, for spotting a leak, and the compressor to know where the timber is at. I'll write it all to a CSV file too in case I ever need to view the whole lot but hopefully the node-red graph/charts display enough to never need to look.

I have a friend quite experienced in drying mixed loads, he doesn't follow any kiln schedules but rather brings the compressor set point down a little as everything equalises, which he monitors by the compressor duty time reducing, and I guess this is a sensible approach?

If there's anything you kiln experts think you'd like to have at your finger tips, if you could have it all on a screen in front of you, let me know. Kind of hard to know what you don't know.

Sensor I'm starting out with a dht22 like you did just because it's easy and they're everywhere. I see they make a less common one dht21 which is supposedly a bit more robust. Permanently wired and inside a case, it's what's on the end of my inkbird dh controller and I was told it would suit fine for the environment. Seems the chip in it sends more bits than the rpi is expecting (when using dht22 library) which pushes the first few important bits out of the array and gives a borked reading, definitely fixable in the library but I'm not experienced with stuff like that and it would be a slow grind for me to modify.
Sensors are easy enough to swap out anyway, I've no doubt they'll fail but if the dht22 does a few cycles and is a few dollars to replace then it's a non event but if they crap out mid cycle I'll replace it with something decent.

Did you expose your rpi to the web to view from anywhere or leave it behind a router? That's another thing that's got me head scratching. I'm not experienced in internet security I know forwarding ports to the rpi without securing it first is asking for trouble.

Did you ever get anywhere with this @Crusarius ?

[Crusarius]

Nope. Without rereading the entire thread I think the last part was to remove the skylights in my roof so they can go into a solar kiln. I finally got the steel I need to do the roof but now its raining and snowing non stop so removing the skylights is not real high on my want to do list.

I do have more time on my hands now but I think I will focus more on my CNC and trying to setup a side gig so I do not have to go work for anyone anymore.

[btulloh]

The dht22 is the easy choice for sure and cheap. Swapping out wouldn't be a financial burden. The problem with them if i recall correctly is degraded accuracy more than total failure. Id have to research again, but there's plenty of info published on them. See how they work for you.

I guess I documented the fact that I used the ds18b20's for temp and i find them to be very dependable and I like the way the work and ship data. No major reason why you can't use the dht22 for temp though.

Can't recall the data bits issue.  I think wrote my own uart routine rather than using the library. Maybe that's the reason.?  I'd have to go back and see what I did.  I think there's a crc test that can be used to verify data integrity.?  I'll see if I can dig up my work on the thing.

Web data - yes can be a security issue, but won't be difficult to manage that if you just push the data to an iot server.  Lot's of free ones out there for users that don't need to push a ton of data. Just look up "iot server free".  Main thing is the kiln needs to be in range of your wifi or you'll have to add something for cellular data.  Not expensive to set up that type cell account for this little bit of data.

[JoshNZ]

I think I read their natural degrade in accuracy is something like 1% per year, would be no trouble to swap them out even every 6 months. I'll probably find an industrial grade sensor anyway.

This is where I have got to with my controller. All pretty straight forward and simple to use. I've been delighted the whole way through with how reliable the board is, amazing how stuff just works the way it is supposed to every time on Linux. The relays all fire as if the switch in the browser page were connected directly to them even across devices.

The interface consists of 3 modules I suppose, the controls and status for each kiln component, the settings to run those components in auto mode, and the data logging. The circulation fans is straight forward, on or off. The auto switches on the other components took a bit of fiddling with, I eventually ended up with a state machine I guess, and needed to store the switch states in the memory and call the auto functions periodically. I found it a bit hard to grasp the event-driven functionality style of node-red and it's possibly not the most elegant solution but it hasn't missed a beat yet. It is being fed random data in the picture below while building it, but the sensor worked perfectly out of the box with the default library.



 

It is a bit bizarre to be designing a kiln controller when I don't know how to run a kiln yet, I'm sure I will figure it all out with time but if the experts here don't mind giving me a starting point that'd be hugely helpful!

1. How many percentage points should I overlap on with the compressor on/off function? i.e. if the setpoint is 80%RH, I don't want the compressor switching on and off each time it gets to 79.9 or 80.1, right now I have it set to start when RH is 4% above the setpoint, and stop when it reaches the setpoint.

2. Should this overlap mentioned above, lets call it setpoint start threshold, be adjustable? Is there ever a reason I would want to change the amount of overlap in the interface or can I just code it to a value permanently?

3. How often would you call the function to resolve the auto settings? I'm thinking every 15 minutes but really have no idea how long it takes before any kind of change might be observed after the heater or compressor starts or stops.

4. Is the vent ever going to be used, practically speaking? If our days max out at 90F in summer and the chamber is in the shade, will I be venting to keep the temp under control?

And have I forgotten anything...?

[wkf94025]

Just found this thread tonight, and excited to read through it in the weeks ahead.  I skipped to the last two pages, and skimmed where you primary contributors are at presently.  Great stuff overall.  Basic background on me and my situation:

• Bought a Lucas swing arm year ago, triggered in part by free Doug Fir following the August 2020 wildfire in Santa Cruz County.  Though I lost a hundred Monterey Pine (good riddance), my house survived.  Shop did not, and rebuild of that spawned much of my current addiction.
• Built a Dr. Wengert-inspired solar kiln, then loved it so much (and had so much DF to mill and dry) that we promptly built its twin.  Each is ~22' x 8' x 4', for about 2,000bf capacity each.
• First experience drying was last summer, Doug Fir timbers (6x6 through 8x12) and some 2x sticks.  First sensor was a nestcam inside watching two glass+mercury thermometers, one wearing a wet wick, and me watching visually.  ;-)
• Put a bunch of Emporia WiFi outlets controlling (1) cheap recirc box fans, (2) louvered exhaust fans (one on each end of 22' long kilns), (3) Honeywell residential DH, and (4) oil-filled electric heaters.  Emporia switches provide on/off from my phone anywhere, and also report kW used by each outlet.  Helpful devices overall.
• All run off-grid, with 6.6kW PV array and lithium storage.  Grid connect came in September, after first DF bake.
• Weighed and marked and measured weekly a 1 cu ft cube of DF in each kiln.  Fun curve to watch.  MC sensor is currently the cheap Amazon General Instrument two-pin widget.  Excited to learn more on this forum about DIY MC systems, especially in-kiln.  Weight sensors a brilliant solution too.  Bring back the Nest cam to watch a bathroom scale?? ;-)
• Now milling, slabbing and starting to dry DF, redwood, white oak, claro walnut, and red ironbark eucalyptus (hope I don't regret that last one).
• First decade out of college I wrote software nonstop, primarily for semiconductor design tools.  Assembly, C, and various OS's, primarily Unix-flavored systems (SunOS, Primos, etc.)
• Played with STM32-based embedded systems the past few years as part of a drone addiction, writing/refining algorithms for lift exploitation in RC gliders.  Bought my first oscilloscope, first solder rework situation, and too many other toys to mention, include cheap sensors of air pressure, temp, speed (pitot), I2C devices, PiCam, etc.  Went waaaay down the rabbit hole of open-source flight control in small, smart, lightweight aircraft.
• Excited many of you landed on the Pi platform.  Such a killer platform for so few $, so few grams, so few cubic inches.  And if caustic [oak] kiln environments corrode them to the point of system disfunction, they're virtually disposable.
• Happy to help guinea pig anyone's UI, drying recipe, sensors, etc.   I am currently using Ambient Weather's sensors for temp and humidity.  $20 AA-powered gum sticks that talk RF to nearby base weather station.  All IFTTT-capable.  Six sensors currently, three per kiln, east/middle/west, some high, some low.  Great way of measuring efficacy of recirc system.  Disposable/consumable if hot, humid acidic environment destroys them.
• Liked the comment about seat-of-the-pants solar baking.  I tend to agree.  Haven't overbaked yet, and a temp-driven louvered exhaust fan ($90 on Amazon) is my circuit breaker, set at about 120*F in the later weeks of the bake.  That said, I don't want to screw the pooch on 2,000bf of claro walnut slabs, so I'll want a proven system on softwoods first (DF and Redwood) before putting the pricey stuff in the kilns.  Not that redwood isn't pricey!
• On the whiteboard not yet implemented:  automated roller blanket that covers the kiln at night, similar to roll-up greenhouse automated ventilation systems seen on youtube.  Kilns lose at least 20*F in a typical night.  It would be great to cut that loss in half.

Stoked with what you have all done since this thread started several years ago.   Hoping to contribute in 2022 some how, some way.

Kelly

[wkf94025]

4. Is the vent ever going to be used, practically speaking? If our days max out at 90F in summer and the chamber is in the shade, will I be venting to keep the temp under control?

This reminds me (with a smile) of the first week after we built our first solar kiln last June.  Painted all black inside and out, south facing in direct sun, 2x4 walls, 2x8 floors, all caulked and insulated with glass bats, and dual-pane polycarbonate roof panels.  With no ballast (i.e., wood load) in the kiln, it hit 160*F very quickly.  Realized that a runaway summer bake could destroy a load, so we installed temp-triggered exhaust fans on each end (900+ CFM, $90 on Amazon) which gave peace of mind.  

[JoshNZ]

Sounds like we'll all be using your setup in the not too distant future - you're welcome to use my software while you develop it lol...

What did you think of those louvre vents? Do they last/operate smoothly/seal properly/stay closed in storms etc?

[wkf94025]

Sounds like we'll all be using your setup in the not too distant future - you're welcome to use my software while you develop it lol...

What did you think of those louvre vents? Do they last/operate smoothly/seal properly/stay closed in storms etc?

I am a huge fan of OSS (open source software) and happy to share with anyone with similar interests, especially those who contribute in any meaningful way.  I may take you up on bootstrapping from your beachhead.  ;-)

The louvered vents have been great.  As to longevity, they've only been installed ~8 months, so no meaningful data there.  When we really want to cook, we use cardboard + duct tape to seal off the opening so outside air flow doesn't blow them open.  Orienting them to exhaust against the prevailing wind direction helps keep them closed naturally when not asked to exhaust.  The long (22') axis of my kilns point upwind, and the vents on each end blow upwind, so fresh outside air is drawn in on the downwind end by the "east vent", and hot humid air expelled in the upwind direction by the "west vent".  The fans are plenty strong alone (900+ CFM each), much less together, to effect a complete climate change inside in ~30 seconds.

[JoshNZ]

Only $90 to buy and $110 to ship to NZ :(.

I'll find something similar over here. I'm back and forth about whether to rely on gravity or actuate something that seals better with an actuator or solenoid, I don't know.

How did you go through the wall with all the wiring?

[wkf94025]

Not sure what you're asking with your last question.  My crass answer is "with a drill".  
Please clarify so I'm not tempted to be crass.   We have romex on the outsides of the tall/north wall and east and west end walls feeding into 110v outlets that are flush on the inside of the kiln.  Walls are 2x4 framing, so typical wall section, sheathed with 1/2 CDX plywood both sides.  Exhaust fan boxes are external to the kiln volume, with fan face and louvers in same plane as inside wall of kiln.  I'll get some photos up soon.

PS:  bummer about cost of shipping.  Where in NZ are you?  Spent a month there in the 80s, and could live many places there in a heartbeat.  Oh wait, you no longer allow foreigners.  :-[

[JoshNZ]

Haha I suspected a drill might be the tool I'd use. I meant how are they sealed, I've gotta get 5 cables through a reefer container wall and don't want to just bore a big hole and bodge it full of silicone, wondering if there's a proper way to do it, a panel box with grometed holes for individual cables or something like it

[wkf94025]

...a panel box with grommeted holes for individual cables or something like it

That's what I would do.