Kiln temp and humidity logger using the Raspberry Pi platform

btulloh · January 09, 2018, 08:50:38 AM

Glad to hear your goodies are finally on the way.

Thanks for the pics from the lake property. I guess I shouldn't complain about snow and cold weather we have here.

By the way - DON'T install Cayenne on your Pi! (I mentioned Cayenne app earlier - it can control the Pi from your cell phone.) It is not well designed and wastes resources - even when you're not connected. It is also hard to get rid of.

I hope your package gets there soon.

btulloh · January 09, 2018, 09:05:54 AM

Thursday I should be receiving some DS18B20's and a relay board. I need to come up with a proper wick and reservoir to make the wb thermo. I wonder how you keep the reservoir from freezing during cold weather? The wb doesn't need to function below freezing, but it needs to survive without baby sitting.

Today I should be able to test the wifi range. My kiln is pretty close to the house and well within range for my cell phone, so I'm hoping the Pi will be fine. I've seen where people have installed an external antenna, but that's just another project.

HD has 12x12x4 plastic NEMA box in stock which should be fine for an enclosure. I'll need to work out some ventilation issues. We'll see how that goes.

Uh oh - thinking again. Danger! It's certainly possible to rig up something on the Pi to take resistance measurements. And do some calcs. And look up things in charts. And compute moisture content. Is this crazy? Is there enough data available to build in a viable wood moisture content monitor? And . . . maybe some load cells to weigh kiln samples. ?? Whoa Nelly! Calm down!

Crusarius · January 09, 2018, 09:22:24 AM

no, no, don't stop. Keep going

ChugiakTinkerer · January 09, 2018, 11:19:51 AM

:D :D :D

I saw somewhere that cotton shoelaces make a good wick. They are certainly affordable.

You could also hook up an ultrasonic transducer and measure the time it takes to bounce a signal off the end of your stack of lumber. An increase over time means the stack is shrinking, yet another indicator of moisture content... 8)

Crusarius · January 09, 2018, 11:22:13 AM

if your gonna use size could always use laser measure

btulloh · January 11, 2018, 04:27:09 PM

I've been trying to catch up on chores and running errands for a couple days. Not much work getting done on the data logger. A little, but nothing too exciting.

Today I got some more sensors and stuff. Five of the DS18B20 waterproof thermos, a light level sensor, the relay board, and some terminal strips to help with the wiring. I have add some things to the software to support the new sensors and relay board. The biggest task is to get the Pi mounted in an enclosure and wire it to the terminal strips, then install it all in the kiln.

CT - I hope you get your package soon.

ChugiakTinkerer · January 12, 2018, 02:20:29 AM

Nobody loves me. My order with SparkFun doesn't appear to have shipped yet either. I'll try a call on Friday to see what's up.

It's busy season at the property. Even if my goodies arrive tomorrow I probably won't get much done this weekend. Going to take advantage of the three day weekend and get some work done on my guest cabin. Or clear some trees. My wife wants to go to town on the trees at the site where we want to put the main cabin. So we'll see what the boss wants and go from there. 8)

I may surprise her with a battery-powered chainsaw, if I can find one in stock in town. So not much progress likely on the electronics front.

UPDATE: I called SparkFun and they apologized for the delay, apparently my order got put on hold by accident. They upgraded me to priority shipping, so hopefully it arrives soon.

btulloh · January 14, 2018, 09:20:39 AM

That's got to be frustrating. Getting your stuff shouldn't be the hard part of the project.

In the meantime, maybe you could do some poking around in the IoT server world. I'm using ThingSpeak.com currently, but I'm not convinced it's the best choice. There are plenty of options out there, even for free. Amazon (AWS), Google, and many others. It's a bit of chore just to figure out who offers what and what the specifics are from one to the next. ThingSpeak is limited to 8 data fields, plus I don't really like the lack of choices on setting up the screen. Plus some other limitations. Not bad, but there must be better options.

I'm working on wiring right now. Not that interesting, but important. I'm making a breakout for the GPIO to terminal strips that can accommodate all the sensors. There are some off-the-rack solutions out there, but I don't have them and I don't really like any of them any way. Ultimately I will probably make a PCB specific to this project.

I have tested the DS18B20's and they work well. I'm going to integrate the code for them into the project today. I haven't worked on a wet-bulb setup, but that's on the agenda. I'm thinking the math won't be that big of an issue in the Pi environment, but I'm not quite clear on whether some of the inputs to the equation are constants or not. If they are all constants, it's doable. If they are not constants, then how can a chart be accurate unless the only variables are wb and db?

scsmith42 · January 14, 2018, 02:44:26 PM

Guys, I think that this is a very cool project, and have a suggestion for you to consider.

For years I have felt that there were some significant improvement opportunities in managing the lumber drying process for small operators. The oven dry sample board method is unquestionably very accurate, but it requires time. Traditional pin type moisture meters are not accurate above FSP, yet most of the damage that can occur during the drying process takes place above 35% MC.

What I think that significantly improve the accuracy of the KD process is to add a system to measure the weight of your kiln carts (or stacks) as they dry. Compression load cells are readily available that can provide input measurements to your Aurdino or Raspberry Pi systems and by incorporating in weight measurements into you kiln management systems you can use your RaPi controller to change kiln settings as necessary in order to achieve a targeted daily drying %.

If you start with a known board footage of your kiln load, you can determine how many lbs of water you want to target for daily removal and manage the drying process accordingly. You can then calculate the MC% of the lumber based upon it's weight, and automatically change the temp and RH% based upon the actual MC% of the lumber.

To me, this would be the next step in the evolution of kiln drying methods.

Scott

btulloh · January 14, 2018, 04:25:03 PM

That is an interesting idea. Thanks for bringing it up.

It would not be hard to manage the data from the load cells. Setting up a kiln with load cells could certainly be accomplished, especially if you baked it in at the construction phase. It would take some design and engineering, but not too overwhelming.

The hardest part would probably be establishing the weight of the lumber pack itself minus the pallet, stickers, etc. All of that is possible. I guess the thing to determine is whether the benefit is worth going through all that. Hopefully this will start a good discussion. I'd love to play with some load cells.

Looking forward to hearing from others about this.

(If this was about grits, there'd be 50 replies before dark tonight. :D)

btulloh · January 14, 2018, 04:35:31 PM

In the background I have been thinking about using some load cells to keep track of sample boards in the kiln. This also presents some challenges. I didn't want to spend too much time on that because it's outside the scope of the original project. (Feature creep.) If it starts a lively discussion though - GREAT!

Would monitoring the whole pack be better? Easier to implement? If monitoring samples only, how could you do that if they are in the pack? Can you treat the whole lumber pack like a sample? Can you get enough data about the pack before it goes in the kiln to make it meaningful? Beats me. Jump in.

Crusarius · January 15, 2018, 07:37:34 AM

I would make a rail system on the floor for the carts to sit on and roll in and out. Put 4 load cells under the rail system. Measure all your lumber carts or pallets and mark the weight on them. When everything is placed in the kiln it will roll in on the rails real nice and you will get your weight measurement. Then the rest is in the programming.

Here is the real question. What would be the most accurate way of measuring?
Weight
Size
Pin type gauge
all of the above

With the pi it won't be hard to add all of this just going to take a little more time and money. If it was me I think I would want all of it. But I work in an industry where more data is better. The crazy thing is if you add all those sensors you could add a little more and make the kiln 100% automatic.

even if you did not do a rail system you could do 4 pads with load cells and just set your skid on that.

This has been my random convoluted mess of ideas in no particular order. Thankyou. please drive through.

ronwood · January 15, 2018, 09:45:58 AM

Can you purchase load cells that have the range required to handle the weight of the stack of lumber? I looked online yesterday and I only found some units that handle about 200 lbs.

Crusarius · January 15, 2018, 09:52:50 AM

you can buy truck scales that will more than handle a full load. they are the same load cells with more stuff around them. they come with 4 or 6 pads to.

Crusarius · January 15, 2018, 09:53:35 AM

ouch truck scales are expensive.

btulloh · January 15, 2018, 06:02:56 PM

It's possible to get the load cells. That's the easy part.

I was expecting a little chatter about this from some of the experts. Perhaps that means it's a cure for which there is no known disease. Maybe there is no reason to look beyond existing methods. Or maybe it's just they haven't been on the forum for a while. In any case, it's been pretty quiet on this thread.

btulloh · January 16, 2018, 02:11:17 PM

I started working on the wet-bulb setup. My first wick was not effective. Need to get better a wick. I do think the waterproof'd DS18B20 will work well for wb. To be continued.

-- Got the light sensor working correctly on the I2C bus.

-- Now there are four DS18B20's and one DTH22 hooked up and working on the test rig. That is the configuration I'll use when I install this thing in the solar kiln.

The biggest job ahead is to get this installed and wired in the kiln. Plus the wb/db calcs to get the kiln humidity reading. Weather is not really cooperating with outdoor work and kiln installation. I'm going to be accumulating the necessary items for installing this thing and continue to work on the wet bulb setup.

I know all this is not needed to operate the solar kiln, but I am interested in tracking the data - just for science. Having the ability to easily check temp and humidity will be very handy as well. Plus I get fan control as a nice side-effect.

ronwood · January 16, 2018, 03:41:04 PM

Could you use the same material that is used for kerosene lamps?

Don P · January 16, 2018, 04:34:34 PM

How do you get the evaporative cooling on the wb when the fan is off?

btulloh · January 17, 2018, 08:47:17 AM

Ron - The wick needs to be tubular. Lamp wick material may be ok, but it needs to encase the sensor. I may have to break down and buy some real wetbulb wick. Not hard to find, it's just not laying around the house right now. I see people using cotton shoelaces, but apparently the shoelace I used had the wrong fiber content. I'm sure the nature of the wick affects the accuracy of the measurement.

Don P - That's an important question. Evaporation still occurs with no air movement, but the rate will change. My experience with wet-bulb thermos is pretty limited and consisted mainly of taking a reading and looking at a chart. This is my first go at making one and using it in a kiln. It may need to be put in a housing and aspirated to get consistent measurements. I have to do some research, unless somebody jumps in here with the answer. Ugly weather here today. Good weather for research.

Initially I'm going to put one of these DHT22 devices in the kiln as well, which measures both rH and temp. It will probably fail or deteriorate, but it gives me something for comparison. Deterioration will be more of an issue than complete failure of the device.

ChugiakTinkerer · January 19, 2018, 02:09:29 AM

Got my goods today. Now to play catch up!

btulloh · January 19, 2018, 08:28:01 AM

8) smiley_horserider Good deal, CT. I'm looking forward to seeing your progress now that you have your stuff.

Got some nice weather coming this weekend. Time to start installing this thing in the kiln. I haven't done anything more with the wet bulb thermo. For now I'm going to put the allegedly fragile DHT22's in the kiln. I can always work on the web-bulb setup as time permits. The kiln is empty right now, so it's a good time to do the wiring. I decided to use a plastic power tool case to house the RPi and whatnot. I have a good selection of them, since everything you buy seems to come with a molded plastic case. One of them will be just right. And free. Maybe by next week it will all be setup and gathering actual data on the kiln.

ChugiakTinkerer · January 22, 2018, 02:17:47 AM

I've got Raspbian installed and started some very basic circuit building and programming in Python. I was able to at least turn an LED on and off as shown below.

I've got a DS18B20 waterproof temperature sensor wired in as well, but I'm not seeing it in the W1 bus. The problem I seem to have is that I did not purchase any 4.7k resistors. The one in center foreground trying to be a pull-up resistor is only 330 ohms. As I type this I realize it almost sounds like I know what I'm talking about. If that's the case it's only because there are some very thorough tutorials out there.

I'm going to swing by Frigid North Electronics tomorrow and pick up those resistors as well as a new soldering iron. I've got to do a little prep work on the BME280 sensor before I can use it. Need to solder in a header on the wee little breakout board. With the state of my vision I'll pick up a magnifying third hand helper station too.

btulloh · January 22, 2018, 08:50:19 AM

You're on your way. Those BME280 sensors are interesting. I wish I had gotten some of those.

When you get the proper pullup resistor you should be fine.

I started wiring and installation in the kiln. Nothing too exciting to report, just wiring and drilling holes. I re-wired the fan outlets to switch them with the relays and got the a/c out to where the box with the Pi will be mounted. Not interesting enough for photos. Most of the weekend was spent catching on up chores outside since the weather was so nice.

GeneWengert-WoodDoc · January 22, 2018, 05:14:23 PM

Back in about 1975, I developed a load cell weighing system that weighed an entire pack of lumber using load cells. The main issue was the long term drift of the cells, so we did rezero every few days. The system had an automatic kiln temperature system based on load cell info. The control system used proportional, rate and reset.

Prior to that, Delmhorst had an automatic system using two sets of pins driven to different depths, called the Kiln-Mo-Trol. They have an updated version now. It works well indeed.

Prior to that, the Moore Dry Kiln Company had a system called a Kiln-boy.

Subsequent to 1978, Bob Little at the University of TN developed a system that weighed the individual kiln samples. The weighing system again had long term drift and temperature issues. Also Lignomat developed a computerized system using pins.

Since that, many others have approached this problem of getting MC of selected pieces in a load. I saw one where the sample was hung on a wire and the wire ran up and outside the kiln so the load cell was outside the kiln. Kiln schedules are based on the wetter lumber and not the average, so weighing a pile is not sufficient.

After many tries, including measuring the energy input and measuring temperature drops, the best system we have still involves individual sample selection and weighing. Once on the scale, computers are used to calculate MC, determine drying rates, establishing correct kiln setting$3so the job of using kiln sample boards is pretty easy now, with just a few minutes of labor each day.

Note that very precise MC is not usually required in lumber drying. Further, most of the time, precise temperatures and humidity is not required. Further, almost all defects occur at high MCs, so fancy controls for air dried lumber are a waste of money as they do NOT improve drying quality or time.