Terrarium growing experiments

[Metallising]

I can't tell how accurate the humidity sensor is but it's probably good enough for most applications like orchid cultivation. The manufacturer states accuracy: ±3%RH and Sensor stability: <0.5%RH/yr

For calibrating I put the sensor inside a zipbag with wet paper and set the humidity to 99%.

More important than accuracy is stability in my opinion, so even if humidity reading isn't accurate I learn correlating plant response to what the sensor I have is reading.

You can buy a replacement sensor and check if you think it's worth trying.

I don't know what CFM the fan is providing, at max speed (12V) probably around 30CFM as I believe this is the average value for 80mm fan but as I'm running the fan at 5V it's probably pulling around 10-15CFM. I don't run it faster as the terrarium is in the living room and I don't want to hear the fan.
I control fan speed with an adjustable voltage adapter, cheap and easy to change settings but impossible to automate like pwm fans.

After reading your posts, I changed the fan position to point it at the glass and instantly the leaves of most orchids started to gently move in the breeze, so I'm sure airflow has improved, it seems distribution of air circulation is more even and there are no dead spots.
Something I will start doing is to increase fan speed for a few hours after watering to help with evaporation and aeration.

Later I will add a second fan, a misting system and a delay timer relay.
Every time the misting system is activated (let's say 1 minute every 2 days), a second fan would kick in triggered by the misting system circuit.
The delay timer relay would receive the signal input from the misting pump and trigger the second fan, which would be running a few hours even after the misting system turned off, the time is set in the delay timer relay.

I have done something similar in the past with these: AC 110V 220V Infinite Cycle Delay Timing Timer Relay ON OFF Switch Loop Module F | eBay

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[Draikan]

Originally Posted by Ray

If you do your research, you’ll find some manufacturers who test and certify their devices. Besides, 85% versus 90% RH is not significant.

I want to respond to this because I agree with it, but I also feel like there are some finer points. I don't disagree, it's basically true, but I don't think it's the whole story either.

85 vs 90, sure, maybe the plants grow almost the same. What about 75 vs 80, probably also fine? 70 vs 75, might start to impact some sensitive plants? And how much error is too much? 5% is probably fine. 10% meh. But 15%, that could cause problems.

Now if you check your plants everyday, and really understand what they need, maybe this isn't such a big deal. But for automation, "trust" is really critical. You need to be able to trust that the system is behaving as expected. Otherwise you have to check on it, which defeats the purpose of the automation.

In my opinion, this means you need a component that exceeds your application's requirements by enough that even at it's very worst it still meets your needs. There are a bunch of different types of error a humidity sensor can have in the measurement, a static offset of +5% across the whole range, error that increases at extreme humidities, even error that varies with temperature, or other kinds.

I think this is what Metallising was saying:

Originally Posted by Metallising

More important than accuracy is stability in my opinion, so even if humidity reading isn't accurate I learn correlating plant response to what the sensor I have is reading.

There are some types of error we can ignore. If the sensor is always wrong by the same amount, you can still get the system dialed in. But if the error changes over time you might be in trouble.

And that's exactly why I've been so focused on the humidity measurement. The specifications for humidity sensors are not as simple as just +/-% accuracy.

I am using the SHT35: https://www.sensirion.com/fileadmin/..._Datasheet.pdf

Reading these specifications, even for a tested, certified, consumer facing device can be hard. Manufacturers want to tell you how their device is good, not how it is bad.

So here is page two:



0 to 100% RH, +/-1.5% accuracy, <0.25%RH/yr sounds amazing, except for footnote 7. Footnote 7 points to section 1.1:



So the "fine print" here is that the sensor will only meet those specifications if kept in the 20% to 80% range. Operating beyond 80% humidity, they give +3%RH error in just 60 hours as an example.

This is one of the most detailed specifications I could find for a humidity sensor. Most manufacturers just don't include this information, but all humidity sensors built with similar technology will have this issue. This is a capacitive sensor, and almost all hobby or commercial grade sensors I'm aware of use this same technology. That includes the inkbird, DHT22, SI7007 from Silabs, HDC series from Texas Instruments, all of them.

It may seem like I'm going overboard focusing on humidity accuracy. I'm really just trying to build a sensor that I can trust to be stable over long durations. If I build something that has to be checked every few days, I'm just making more work for myself, and creating unreliable tools that are more likely to hurt my success than help.

I'm aiming for +/-3%RH after years in a >80%RH environment, including occasionally getting sprayed with water. This is what I currently feel is acceptable for my terrarium growing goals. The accuracy also helps me share what I'm doing with other folks. If I tell everyone I'm having success at 80%, but the real RH is 90% (that
is a 2x difference in VPD!), that's confusing and hard to replicate.

[Metallising]

Originally Posted by Draikan

I'm aiming for +/-3%RH after years in a >80%RH environment, including occasionally getting sprayed with water. This is what I currently feel is acceptable for my terrarium growing goals. The accuracy also helps me share what I'm doing with other folks. If I tell everyone I'm having success at 80%, but the real RH is 90%, that's confusing and hard to replicate.

The inkbird does just that.
It's widely used by amateur and semi professional mushroom cultivators in >90% environments, everyone I talk to is happy with it.

You can get replacement sensors and change once a year if you don't want to risk inaccurate readings, or just use the replacement sensor to check if the readings are matching with the old sensor. That's what I do.

Growing orchids in terrariums involves many variables, in my opinion isn't worth to spend too much time or money for a small improvement in humidity reading.

[Draikan]

Sounds like I should try an inkbird!

Maybe I'll do a side by side when I get my next batch of sensors...

[DirtyCoconuts]

i prefer to let the tank go to 99 and then use other means to bring it down.

then i am not kidding myself about the fact that it is SOAKED by clouds every night. its all a balancing act though and that is why i feel like the more automated you get it, the more likely it will have an error.

the stuff D has been making blows my mind but id rather just use my basic sensor and my eyes and nose.

[Draikan]

Originally Posted by DirtyCoconuts

i prefer to let the tank go to 99 and then use other means to bring it down.

then i am not kidding myself about the fact that it is SOAKED by clouds every night. its all a balancing act though and that is why i feel like the more automated you get it, the more likely it will have an error.

the stuff D has been making blows my mind but id rather just use my basic sensor and my eyes and nose.

I think this matches my impression of how the plants want to be treated, we are just going about it slightly differently.

Watering to saturation and beyond seems to be a good thing, both because it flushes out the mounts, and because "soaked" is hard to mess up.

It's the period a day or so after soaking everything that I'm still working on. In my climate, at this point the mounts have dried out a bit and humidity is dropping. As humidity keeps dropping, the conditions can go outside the ideal range, especially if it's hot, or dry, or the heater is on.

The obvious answer is probably to turn down the airflow, or reduce ventilation. I don't want to do this because the plants seem to benefit from the higher airflow while they're very wet, so long as it doesn't dry them out afterward.

This is what I'm using the humidity sensing and control for, to prop up the minimum humidity between waterings, allowing me to provide lots of airflow without drying things out too far.

I want it all, lots of air and high humidity haha.

---------- Post added at 07:00 PM ---------- Previous post was at 06:30 PM ----------

Originally Posted by Metallising

The inkbird does just that.
It's widely used by amateur and semi professional mushroom cultivators in >90% environments, everyone I talk to is happy with it.

You can get replacement sensors and change once a year if you don't want to risk inaccurate readings, or just use the replacement sensor to check if the readings are matching with the old sensor. That's what I do.

Growing orchids in terrariums involves many variables, in my opinion isn't worth to spend too much time or money for a small improvement in humidity reading.

I took a closer look at the inkbird, because based on my current understanding of their sensor, it should not be capable of stability like you're describing. (Not saying you're wrong, just that our experiences don't match, maybe an indication that I missed something?)

It was a bit of a rabbit hole.

This is the specifications section of the product page:



Fortunately they provide the part number for the sensor, fantastic. A search turned up the datasheet:



This datasheet is old (2007) but it already has some promising claims. It looks like Humirel is the humidity sensor division of a French company called Measurement Specialties. They don't have a website anymore, apparently they were bought by TE in 2014:

TE Connectivity to Acquire Measurement Specialties, Inc.).

So I found the current datasheet from TE, available here:

Access Denied

And this has some good stuff in it!





From these red highlighted sections, I think TE is claiming that this sensor will remain calibrated through prolonged exposure to high humidity, including liquid water (condensation).



Inkbird is using the HTG3535 so it actually does have a PTFE membrane, which should make it resistant to water spray.

I'm honestly pretty surprised that this sensor wouldn't suffer from long term drift. Maybe Humirel developed a slightly different technology for the sensing element that doesn't have such an issue with high humidity. I contacted TE with a bunch of questions about this product, so we will see what they say.

One of their more recent offerings is the HTU21DF, which makes similar claims about high humidity and condensation tolerance. It would probably use the same type of sensing element as the HTG3500 series. I can get them here in a prototype compatible state:

Adafruit HTU21D-F Temperature & Humidity Sensor Breakout Board ID: 1899 - $14.95 : Adafruit Industries, Unique & fun DIY electronics and kits

Depending on what TE says I may have to test a few.

Thank you for pushing me to take a second look at what inkbird was using. I had dismissed them initially, but they may actually be the only plug-and-play humidistat available (as far as I know) that is suitable for our conditions.

[DirtyCoconuts]

Draik, can I call you that? Do you mean airflow or ventilation?

I ask because a recent insight I gained from Ahkenaten was that air movement within a tank is as important as the circulation of outside to inside air. His was a cloche but had a fan inside. Nothing stale but nothing fresh....

So are you bringing house air in? Letting tank air out? Or just referring to the turbulence created within the static growing tank?

Based on the above post, I am way out of my sand box and I apologize I am like a simpleton who has wandered into the salon

[Draikan]

Call me whatever you like haha.

That's a good clarification. I'm using active circulation (internal airflow), and passive ventilation (exchange of air with outside the tank.

I'm trying to get lots of circulation, I think this is what the plants really benefit from. I haven't seen evidence from my plants that they actually need much "fresh" air from outside the tank. I really only want a small amount of ventilation, just to very slowly dry off the leaves and prevent humidity from sitting at 100% in a completely closed container.

But circulating the air in the tank does increase the ventilation. If I turn the circulation fan way up, it mixes in more air from outside.

[Metallising]

Draikan, if you ever try the inkbird sensor, check what people (including me) are doing to extend sensor life time.

[Orchidtinkerer]

Draikan that is some good info on the sensor info - like you say it is hard to find for most manufacturerers and the reason is because their sensors will be worse than those specs. Only the menufacturers proud of their specs tend to publish them and others will be worse!

You say they are all made the same, to a point maybe but some perform worse than others. I have 16 sensors at mine. Some are better than others. They are all fairly basic cheap ones and should in theory have the same components so either those components are put together differenctly or there are differences.
Like some sensors update every 10 seconds, others every minute, then some are super sensitive picking up changes instantly, others take an hour to slowly adjust to the change.

To me that is fairly significant changes. I am no technical expert and have no idea what is in the sensors, none are going to be super reliable but having a reading even if 5% off is better than no reading at all imo.

I think a manual sensor is a good asset too. I have just ordered myself a couple more.

The worst thing I discovered recently was that a sensor was not reading high humidity well in one of my terrariums so it had been running too high, not just 5%.


On a sidenote to the fans. they are not all the same either actually. Mine are all 80mm.

I have a 5v 0.15a fan, they run very slow but are the cheapest
then I have a 5v 0.2a fan which is also fairly slow.
then I have a 5v0.3a fan which runs about twice as fast the the first fan and can move a decent amount of air.

If I need more than than I use a 12V 0.2A fan which pushes a huge amount, gets a bit noisy, it would make more sense to use a 120mm fan as it could move more air silently but it's all an added cost so for now the 80mm will do.

as you can see the first fan uses 5v x 0.15a = 0.75Watts
the fast fan uses 5v x 0.3A = 1.5W
the fastest fan uses 12V x 0.2A = 2.4Watts

All are 80mm but I can get different speeds using different rated fans.

the best cheap fans I have found so far are generic usb router cooling fans. They run at 0.3a, are super silent and cheap