Crafting an electronic psychrometer

[AlexOk]

So far I have calibrated my hygrometer always with the salt-method. This works quite well with normal (small) hygrometers. But it is not really practical for my permanently installed humidification-system in the humidor cabinet.

Therefore I have now built an electronic psychrometer. It consists of two electronic thermometers and an Arduino. So I can quite easily calibrate the hygrometer in the cabinet.
Maybe this is interesting for some in the forum. In my blog I described the construction in more detail.

[oliverdst]

This is great, man.

[tjohn7]

Very impressive!

[PigFish]

Very interesting mate, thanks for sharing. Have any idea how accurate it is? -Piggy

[skunkmilk]

I am also intersted in the accuracy. It looks like you've done quite a bit of research. I sketched a few arduino projects regarding the automation of the humidity in my humidor, but they never got to the work bench.

The humidity sensors I've researched said they were up to 5% innacurrate. So trying to hold at 70RH could be anywhere from 66.5 - 73.5RH. That sounded like a bit much. The best sensor I could find, within a reasonable price point at $40, was the SHT11. I believe the SHT15 is the new one. It's accuracy is still +/-3.5%, which seemed a bit much after shelling out $40. Granted, it has a built in temperature sensor to increase accuracy.

Sorry, I geeked out there for a second... carry on.

[PigFish]

Accuracy, for my projects and business, is just something that you buy… It is a better glue, a stainless screw verses a nickel plated one, or a better grade of chocolate.

It appears to me, that when one is back down to having to read different settings, once more based on the accuracy and precision of temperature and barometric pressure, you are back in the same boat.

With that said, I still say kudos to the OP, it is a neat project.

Accuracy is one of these, who has a faster gun, game. You can sink tons of money into it with little return. Ultimately, whatever your settings may be, you are going to have to settle on one somewhere and get to smoking your cigars. Your cigars then, along with your tastes, will be the final arbiter of your settings…

Since we discuss settings on the forum all the time, and you never know if the guy to whom you are addressing has the same love for accuracy, you find yourself right back in the same situation except now it is a communications barrier, where there are errors between two or more parties. I have simply worked it down to a simple rule. I never believe my customer knows what his settings really are. I address every problem around what data he can give me about his cigars and not his instruments.

For me, precision control is more important than the best accuracy. I want consistency… Since all electronic hygrometers creep, one should look to replace them about every two years. I buy temp and humidity transmitters that have replaceable sensors. The sensors themselves are the most expensive parts and it is due to their published accuracy… We come full circle!

I still think this is a very interesting project!

-Piggy

[AlexOk]

Have any idea how accurate it is?

I use the psychrometer only for calibration. When measured over 30 minutes (one measurement per second) I had a variation of no more than 0.5% RH. But I work with a mean of 10 values ​​so such outliers were smoothed.

I am very satisfied with the accuracy.

In the end (for me) it is no matter what exact moisture I have in the humidor. I am not a number freak. 71.8% RH or 72.5% RH. It does not matter. Important are the cigars. They must have a pleasant humidity.

I am also intersted in the accuracy. It looks like you've done quite a bit of research. I sketched a few arduino projects regarding the automation of the humidity in my humidor, but they never got to the work bench.

You may have read that I moisten my humidor cabinet with a homemade Arduino-humidifier. I have described the project in my blog.

Maybe the description is an excitation for your project.

The humidity sensors I've researched said they were up to 5% innacurrate. So trying to hold at 70RH could be anywhere from 66.5 - 73.5RH. That sounded like a bit much. The best sensor I could find, within a reasonable price point at $40, was the SHT11. I believe the SHT15 is the new one. It's accuracy is still +/-3.5%, which seemed a bit much after shelling out $40. Granted, it has a built in temperature sensor to increase accuracy.

I think there is a small fallacy. The values ​​do not jump. They are linear. As with a hair hygrometer.

In my humidor I use a block with 3 replaceable hygrometers DHT22 (also called AM2303) (see picture). This hygrometer I have calibrated to identical values. I use 3 hygrometer so they can check each other. If the measured value of one hygrometer deviates more than 5%, the value is discarded and the hygrometer is reported as faulty. I need to replace it.

As actual display value I use an average of the last 10 measurements of all three hygrometer. This smooth small fluctuations (no humidor has an absolutely homogeneous humidity distribution). For a mostly even humidity distribution I use a convection fan in the cabinet.

Sorry, I geeked out there for a second... carry on.

You're welcome.

[skunkmilk]

Great info. I'm a novice when it comes to electrical engineering, so it's nice to have information from someone who has built some successful projects.

I believe you may have inspired me to complete that project. Winter is coming and it would be the perfect time to ward off the cabin fever with a project. I bookmarked your site. I'm sure I'll pore over it in the future. Thanks!

[CanuckSARTech]

Very great info to share here! Well done!!!