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Understanding "Activation Logic"

I get more and more questions regarding humidor controllers and what separates the various controllers on the market. This has been written to introduce the readership to what makes a humidor controller tick and how this programming characteristic affects the life of your cigars in your custom humidor.

Understanding the difference and the jargon of logic controllers is the key to getting the system performance that the advanced humidor builder requires. This thread will discuss some of that control jargon so that you as a humidor builder or consumer may have a greater understanding of the controls that you will build into, or have built into your humidor.

There is a lot to be said about what humidor control system is the best. System controls are like other forms of technology; they represent a series of trade offs. Best, does not mean the same thing for all customers. The controller world consists of compromises; those include the cost, features, and simplicity verses effectiveness. You cannot roll 6.5 on a six-sided die! Facets represent complexity. Complexity generally represents resolution, precision, utility and in some cases the difference between success and failure.

Lets start with a few basics. A huge problem with active humidor controls is that most people don't know what they want or need. They see the controller as a switch and little more than that. Complicate that with the fact that most “prepackaged solutions” do not deliver anything but the crudest of switching controls and you could have making of a problem instead of a solution. The “crude” nature of some of these control products can be considered a blessing or a curse depending on your perspective. It is a blessing if you are happy trusting and not really knowing how your humidor performs. That blessing is typically dressed as operator simplicity. It is a curse if you are interested in demonstrating the highest performance of your active controlled humidor. That simplicity, can very well cost you the high degree of precision necessary to make small automated humidors as good as they could be.

So what system is best? The actual answer has little to do with controls at all. The best system is the one that works for you where the cost represents a value to you. As in many cases here, I ask you to ask yourself; what you want to control and why, and certainly how much money are you willing to spend to get you there?

I have adopted this view myself. While I am somewhat obsessed with precision control, it was the search for reasonably priced precision controls that has brought me to where I am at today. Spending thousands on controls was not an option. I have used several types of controllers over the years. As it is my desire to build the best humidors that I can build, that desire has driven me to look for better solutions than the current crop of “off the shelf” humidor controllers while still being competitive with them.

Not all systems are equal, neither are all controllers. An excellent controller is at the heart of an excellent system. However, an excellent controller does not make up for bad humidor design. And on the flip side, good design will not compensate for a poor controller. Design and control must work symbiotically to build the best humidor. As a consumer you have to judge the trade-offs for yourself. The trade offs start with costs. So, what do you get with your controller dollar? Here are some pertinent points.

Simplicity! I think this is important to a lot of people. It is not really important to me. I would encourage those looking for controllers not to stress simplicity. I have a number of controllers and while the package on some are really nice, there are a number of problems that these controllers cause… cause, rather than fix. The nice package is useless unless it works! A controller should fix problems, not cause them. I have presented my control problems to some of these controls companies in researching controller technology. Unfortunately the answers to my questions have typically been, “we sell what we sell” or “this is what works well for us.” In other words, “We can’t help you!” As a means to fix my problems I worked through various physical modifications to my systems. I use my own switching logic and had limited success. The lesson here is this. What started out extremely simple became complex because I could not perform the function that I wished to perform based on the parameters that I wished to control. All controllers have limitations, but many of these “easy learning curve models” quickly lost their simplicity when they began complicate my projects as a means to overcome their limited utility.

Along with simplicity is design. Design includes everything from size to programming. This is where a superior controller shines and where preconfigured, keep it simple stupid controllers lose their luster.

To keep it simple, a typical controller works around a set point, well, one set point, and two additional "logic" points. This set point, logic points system, has to be considered typical in the controls world. What "decisions" the controller makes around the set point is what separates the heifers from the bulls. The "logic" of when to perform a given function is programmed into all these controllers somewhere. The main question is, “Who supplies the logic?” Unless you have experience with controllers, you might never know about the importance of activation logic. Ultimately, the control over the set point is at the heart of a great controller. The ability to choose your activation logic is at the heart of the best controllers.

For the sake of clarity and example, let me describe the process of a controller product that I own and have tested and describe how the process affects a humidor. This is one of the easy-to-use controllers that I tested in the past.

Most if not all controllers will work around a Set Point. The first thing that must be established is whether the controller recognizes the set point as a high set point or a low set point. This is not a minor distinction and must be considered as a part of the activation logic matrix. Many controllers are programmed with firmware that will determine this for you, making it simple. This is a prime example of why simple is not best. Simple means that if you don't like the way the controller functions, you live with it or throw it out and try something else. If you are cleaver perhaps you can even find a workaround. Flexibility is far more important to a humidor builder than simplicity. Flexible set points and their associated activation/differential logic points are the single most important aspects of good humidor performance when viewed from a controls perspective. I will explain more about this going forward. The set point then, in some cases, does one thing only, and the manufacturer of the controller (or the programmer) will dictate it to you. You see, you can change the set point, but you cannot typically alter the functioning of the controller around the set point with these preconfigured units. The actual trigger points (activation logic) are firmware programmed by the manufacturer. They do this so the controller is simple to use and for other reasons. One “other reason” is so you don't foul up the function of logic of the controller by not understanding its functions. Simplicity is great for the novice... for the advanced humidor builder it is a roadblock to a better working humidor! Simplicity assumes that you are a moron or you are lazy, not capable of managing advanced control options. As a consumer, you have to decide whether superior control is worth the steeper learning curve.

I have outgrown “preconfigured” controllers. Anyone interested in exceptional humidor performance outgrows these packaged controllers very quickly. Or, they just don't concern themselves with the actual operation of their systems!

Now on to the example.

This controller has a set point of 70 dF. You can choose your own set point and it does not have to be 70 dF, I am just using 70 for the sake of the example. As the environment temperature increase, the controller will switch on your refrigeration. We will define this as a High Temperature set point. Ask yourself this. How does the system determine when to start and when to stop an appliance, my cooler for example? My experience with this one type of prepackaged unit (my example) is this first activation logic number is 1 dF above the set point. 71 dF then is the Activation Logic point. Systems don't react instantly. Remember this is real life, not a simulation. The refrigeration begins to cool the coil and the coil in turn starts to slowly cool the environment.

How your controller sees the environment is just part of it. More important is what decisions it will make to change your environment and when it will make them. In our example, the cooling coil continues to run as the system slowly declines in temperature. The cooling coil almost certainly cools below the dew point eventually, and this can take seconds or minutes depending on your cooling system. At or near the dew point the cooling system starts to remove water from your humidor. You see the air conducts heat and transfers it to the cooling coil in order to cool your humidor. That same air contains the water vapor that makes up your relative humidity and that water passes by the cooling coil as well, but in the case of water vapor, it does not just pass by it like the air does. It collects there as condensation and turns to liquid water and either freezes there or drips off your cooling coil. The longer the system runs, the more the air gets cooled and at the same time, the more water gets removed.

So lets say that your humidor finally gets to the point where it shuts off, and in the case of the prepackaged controller in my example, the temperature is now down to 69 dF. This point is termed the Differential Logic point.

We have now defined three points; the Set Point, the Activation Logic point, and the Differential logic point. Now back to the example.

Lets just say that the system has taken about 15 minutes to get from the activation logic point to the differential logic point. The problem; the controller, even with the humidifier running, has run down the rH in your humidor to about 40 rH. I am not postulating here. I know all this because I have built and tested active climate control humidors for many years now. Empirical evidence has shown me, that the longer a system runs and takes to cool, the dryer the system will be at the end of the cycle.

So this controller has done its job. It turned on a cooler to cool the system and it cooled the system! When the system got dry it turned on the humidifier to put water back in the system as well. However, as a result of poor logic control, it has also caused a sufficient drop in rH in a humidor to drive the humidifier for another 5 to 10 minutes to bring the humidor back to your rH set point.

Imagine what your humidor environment is like if it is 80 dF in your office, and your humidor is running once every 30 minutes. 15 minutes to cool, rH down to 40 in the cooling process, another 10 minutes to bring the system back to 60 rH and the whole cycle starts again once the temperature creeps back up from 69 to 71. Is this what you want or expect?

In this example, you no longer have a stable environment. You have a controlled environment, yes, but stability is not a part of it.

Now imagine a controller that you can program yourself to change the activation and differential logic. Do you think that you could change this cycle and the problems that have resulted because of it?

I use an industrial process controller that I program myself adapted for use in a humidor. This is not a fancy gimmicky thing that has logos of smoking cigars on it. It is a straightforward mini computer control for reading sensors and controlling a system based on those sensors. It is what industrial users are using to control cold rooms, commercial food production spaces and the like. You see the people working with industrial controls don't want a controller that decides how to control their environments. They already know how they want their environments controlled; they just don't want to post a guy looking at the parameters with switches in hand ready to control them. Instead they use an industrial process controller, a logic controller, for that kind of work. This is what I use! They perform the same functions as the simple humidor controller; they just perform it better because you have a greater command over more of the control parameters.

What makes a good controller a great controller is the ability to adjust it to your situation. Simplicity is a mindset and is a function of the operator's learning curve and nothing more. The ability to control the logic of a system is more important than how simple it is to set up. That is my opinion. I have a lot of evidence to back it up by the way!

Lets take a look at the way a programmable logic controller behaves now and how it works.

First we choose a set point as before. Lets say it is again 70 dF again. I have more choices to make, however. I have to decide on a set point differential. Unlike the factory set controller in the example above, I will choose for the sake of this exercise 1 dF. If you could control it, the set point differential on the previous example above would be 2 dF. Do you have to choose 1 dF? No you don’t. You can choose any number of points dependent on who makes the controller, 0.1 to 179 (for my controllers anyway)... Frankly, anything under 1.0 is not really practical but you can experiment with any setting you want, that is the beauty of a logic controller.

After the set point differential one defines the activation logic and the differential logic points. Just as a reminder, these are the "turn on" and the "turn off" points. The set point is just a reference point. The set point differential is the maximum spread between the activation logic and differential logic points, just for clarification. With these four settings under our command we have control of not only where the set point is, but the logic that the controller will use with it to turn on and off the system appliances down to as little as 0.1 degree of resolution.

If we work backwards to determine the activation logic of our previous example it would look something like this. The set point would be 70 dF, the set point differential would be 2 dF. The activation logic and the differential logic would be 50% and <100%> of the set point differential respectively.

Going forward, since I don't want to lose you in programming details, I will only look at the final result. In my case I will choose an activation logic number that will activate my controller to start when the temperature is 70.1 dF. What is more I will set the differential logic to shut the cooling system down at say 69.6. With the flexibility of the set point differential system with activation logic, there are actually many parameters that one can use to get the same result. As you can see there are many advantages to a system that allows you this broader range of control. As systems get more complex, such as using cooling to dehumidify the range of control afforded by these systems become absolutely necessary.

In this example alone, you can see that I have much greater degree of control over my humidor. I am no longer stuck with the crude low resolution of a preconfigured instrument. I have the freedom to control the logic and choose various points above and below the set point to initiate and cancel my control cycle.

What is more, I have the same flexibility for all the appliances that are attached to my controller. The algorithm for the differential logic system allows you to simply change the set point, just like the preconfigured unit and retain the same differential activation and deactivation points, again just like the preconfigured system. Additionally however, you can simply broaden the scope by changing the set point differential, or reprogramming the activation logic and differential logic numbers together or separately to gain a whole new degree of control outside of that provided by the prepackaged controller.

You have the same range of control with any of the digital outputs and they easily program all the same way. You want better control of you humidifier... you got it. Want to experiment, you can! You can have the controller, working off the set points and the differential points turn on and off appliances just about anywhere that suits you! Of course, if you don't know what you are doing, you can confuse the controller!!! You can tell it you want heating and cooling at the same time for example, and it will do exactly what you told it to do!!! Assuming you have a heater and a cooler, it will run them both! This comes in pretty handy actually. You can for example, run the cooler briefly to dry the humidor if you live in a high humidity environment, and then run a heater to bring the temp back to were you want it. Humidor in a damp basement, live in the humid south, not a problem?

What can you control with a logic controller? Most of these preconfigured units have only two control points, two preconfigured digital outputs. One point controls refrigeration and the other low humidity. What if high humidity is your problem? You are stuck! Not with a logic controller. Want more function? How about a real time clock that can shut your system down while you are in your office so it does not distract you? How about a timer for timed circulation? Need more options than just controlling low humidity and high temperature? Want to control a cooler, heater, humidifier, and a dehumidifier??? With the right controller, you can do many things that the preconfigured models cannot.

Want to build a project humidor? There is only one choice as far as I am concerned. If you really want a flexible controller that works and will fit your project and your needs as they develop, the right logic controller is the best choice.


The picture shows a couple of my controllers mounted in faceplates. The controller itself is a small package, separate of the faceplates and the enclosures. The lighter is a DuPont Extend that I put in there for size reference purposes.

If you have questions regarding digital humidor controls I am happy to field your questions on or off the board. Happy building!


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Very nice bit of reasoning.

Back when I was an engineer at my previous company, I used to toy with the idea of creating a humidor too using similar type programmable logic controllers.

Maybe when I have more time on my hands. :D

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Ray......wow bud. Awesome work.

Now....looks like you need less free time on your hands! LOL. wink.pngtongue.png

Just kiddin', bud. Glad you're continuing to work on this for the community. Thanks for sharing! thumbsup.gif

... wanna' talk time!

CAD drawing of new sealed coil humidor design of mine. Humidor will, cool, heat, hydrate and dehydrate. This will have a new auto-time circuit as well that will run the circulation fan and desiccant silo to keep all thing homogenous when within the envelope of satisfactory settings. The timer circuit will also act as a means to trigger the humidification or dehumidification of the desiccant to keep them perfectly conditioned.


... hopefully it will work!!! -LOL

This way I won't have to move to Canada to have perfectly conditioned cigars!

Cheers mate! -Ray

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forgive me piggy, i dn't have time today to go through it but will try soon. well done for posting!!

always remember when a mate and i picked up one each of those silver case carriers for cigars from rob. mine has been very useful though as i ust use it for travelling, i have never bothered with the humidity control. i used to drop in some distilled water but on short trips, not sure it makes much difference. but i remember my mate ringing up rather outraged because his humidity indicator would not work (rob later told me that they were never supposed to - it was decoration only). my mate actually submerged his for a week and still couldn't get it to move!

not sure it is relevant but it did amuse me at the time.

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Thanks for the post Piggy, Ive read a lot of your posts around the board on humidification and its good to see you giving me some details on what these logic controllers youre always mentioning are like - cheers!

Imagine what your humidor environment is like if it is 80 dF in your office, and your humidor is running once every 30 minutes. 15 minutes to cool, rH down to 40 in the cooling process, another 10 minutes to bring the system back to 60 rH and the whole cycle starts again once the temperature creeps back up from 69 to 71.


Can you use your second set up with the more customised controller to provide similar example values for the time taken and variance in rH? That would make the comparison of the real world performance between the two clearer to me.


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Thanks for the post Piggy, Ive read a lot of your posts around the board on humidification and its good to see you giving me some details on what these logic controllers youre always mentioning are like - cheers!

Can you use your second set up with the more customised controller to provide similar example values for the time taken and variance in rH? That would make the comparison of the real world performance between the two clearer to me.


I don't know that I understand the question. If I program controller "B" (my controller) to that of controller "A" (the preconfigured type) then I will get the same result as controller "A."

The controller itself is not magic. It is simply adaptable to real time conditions that exist for you.

If your cooler is underpowered (like a TE cooler for example) it cannot fix that! If your cooler is under insulated and you are trying to beat ambient conditions beyond a reasonable limit, it can't cure that either! These both have influence on cooler run times. What it can do, is allow you to decide what limits are reasonable for your circumstances.

Humidors can be designed to try and achieve unreasonable conditions and a logic controller will be your best solution for this endeavor. I build humidors to make stable conditions and they are the best solution for that also. Unreasonable conditions represent a design fault, not a control issue. I have proven (to myself anyway) that unstable conditions can be the result of a poor choice in controllers, not just design issues.

These are a couple of data logs that I have in my Mac. I usually do data log work on a PC. Both are from summer months, albeit different days, therefore it is not as though these were "controlled" conditions by any means. One represents time in the humidor with a preconfigured controller, the other is a test with a logic controller. These are not current as I have stated and frankly I would need to examine my log to see if they were even done in the same humidor but this should give you an example of what I am talking about.



I have no idea today what settings were used in the logic controller. Sometimes I test so rapidly that I don't log the changes with the charts, I just make mental notes and change programming. These charts might as well be charts testing the programming of a desiccant pack for all I know today. The point being... I don't remember what I was testing here nor why.

I hope this helps.

Cheers. -Piggy

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Thanks for the graphs, the first one is likely what i was after.

What i was trying to ask was what were the variances in rH and time taken to right three temperature between activation points using the second set up in your original post i.e. the dF differential from 70.1 & 69.6

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Where can I buy one?

Steve I am an OEM distributor of these for my humidors, they are made to my specifications. This is not a commercial thread or an attempt at one so if your inquiry is commercial in nature please contact me via email in my profile and I will give you all the details you want, the good, the bad and the ugly!!! -LOL

I hardly ever see a PM from here as my box is always at the 99% mark. Please use email and reference who you are on FoH. Active FoH member rate a discount from me.


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Hahah who would have thought my learning in PID loop tuning would actually be brought to light in a cigar forum :)

My wine cooler (30 bottle Vintec) does exactly what you initially suggest. Temp goes up to a point, cooler kicks in, temp and rH plummet, cooler turns off, temp and rh rise, rinse and repeat.

I know the downfalls of the system, but i minimize the risk of instability getting to my sticks by storing all my sticks in boxes (as you suggested in another thread), none are open to the "atmosphere" of the fridge. Boxes i want to store i put in ziplock bags with a Boveda pack.

You talk about stability by basically narrowing the logic parameters. This will work very well, but i've been thinking more towards preventing the temperature fluctuations to begin with (and by logic rh fluctuations). The fridge increases temp because it's absorbing heat from the surroundings. If i could minimise this, then the cooler would not need to kick in. I'm limited to where i can store my fridge in my current house (under a table, close to a wall and drawers). Later on id like to play with putting the fridge out in the "open" to allow heat from the compressor to dissipate outwards rather than back into the fridge. i guess it all goes back to ambient conditions. We all wish we lived in perfect 20C and 70rH all the time so we could have our sticks on our pillows with us when we sleep.

Again, thanks for the learning.

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So, because I'm an over-active member, is that why my prices are higher??? tongue.pngwink.pngdevil2.gifbuddies.gif

... that might affect the sperm count mate, but does not really affect me!!! -LOL

I will discount to members here as a means to support the community and encourage people to partake. But there is allways a possibility of the post once and ask me for a discount kinda' guy!!!

You don't even have to ask! Cheers, my friend. -Ray

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