Terrarium Misting

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Day geckos are arboreal, tropical lizards. Along with leafy trees to to climb and high daytime temperatures, they need a high relative humidity and well misted foilage to lick water from. The challenge is to automate spraying water into a day gecko terrarium, both to keep the relative humidity up, and to provide water droplets on leaves. Automation is important because otherwise manual misting is required twice a day, every day.


Some desireable characteristics of such a system:

  • Spray at regular intervals (3-6 hours)
  • Sustained spray for 15-30 seconds at a time
  • 2-3 day water and pressure capacity; easy to refill
  • Enough nozzle pressure to spray through a screened terrarium cover
  • Relatively quiet pump operation
  • Simple design and operation (fewer parts to break)
  • Inexpensive to build

Existing Products

There are a number of pre-existing products that serve this need, generally oriented towards hobbyists, mostly tropical pet owners and gardeners.

ZooMed makes the Habba Mist specifically for terrariums. It is relatively inexpensive ($65-80), operates with either an AC adapter or batteries, and has both an attached spray nozzle and a single remote spray nozzle attached via flexible silicone airline tubing. There is one Habba Mist review that you can find in several spots on the Internet.

Big Apple Herpetological makes the generally highly regarded Big Apple Misting System ($110), also specifically aimed towards home lizard owners.

WetWorks Misting Systems makes the Mr. Moisture and Mr. Moisture Pro kits ($105 and $210, respectively), which are similar in construction to the Big Apple Misting System.

Finally, Ecologic Technologies, which has a more horticulturist focus, makes a series of misting systems under the Rainmaker line ($170-400) with especially powerful siphon pumps and a large selection of nozzle types. The three latter systems have similar setups: a large plastic water reservoir (2-5 gallons), a siphon pump, some amount of flexible tubing, and one or more nozzles.

Holly and I bought a Habba Mist and it is decent, but not perfect. The pump mechanism is very loud—probably too loud for a terrarium in a bedroom. When routed through the tube, the pump isn't isn't strong enough to send the spray through a screened terrarium cover, so you have to route the remote spray nozzle through the cover, into the tank. There's only one spray nozzle, so it's hard to get full coverage in Holly's 29 gallon terrarium.

Doing it Yourself

For $100-200, it seems like it should be possible to build your own terrarium misting system... and it would probably be a pretty fun engineering project. The primary problems to solve are how to deliver the water in a fine spray, how to trigger the spray using mechanical or electronic means, and, finally, how to automate spraying on a schedule.

Delivering Water

The first problem is how to get the water into the tank—how to power the spraying of the water itself. For a human, this is easy; take a cheap plastic spray bottle, and pump it by hand. Things are more complicated if you want to power the pumping automatically. There is a lot of information on-line about how a spray bottle works, and how waterguns work. There is some great information on the Internet Glossary of Pumps, part of the All About Pumps on-line educational resource.

The simplest design for a water pump would be an elevated reservoir, using atmospheric air pressure to drive the water; this is similar to how a water tower works. This is probably not practical for a terrarium setup because each foot of height gets you only around 0.4psi. For comparison, the Big Apple and Mr. Moisture pumps deliver 55psi pumps, and the Rainmaker series uses 45psi and 100psi pumps, respectively. So, an equivalent system would need a reservoir 20-40 feet in the air, which certainly violates the "easy to refill" requirement.

An air-pressure powered pump seems like a good strawman design. The main concerns here would be good valves, so that pressure leakage would be minimal. My co-worker Jim suggested something very straightforward for just the water pressure problem: a bladder, with a weight on it. This seems like the simplest idea so far. Other ideas: cannibalize a couple small electric waterguns, and see if they deliver enough pressure.

Triggering Spraying

The easiest way to do this seems to be to take an existing valve, and actuate it with an RC car servo or similar stepper motor. Alternately, if we have an electric pump, we can drive it directly or with a relay.

Automating Spraying

Regular hardware store timers and even sprinkler timers are not appropriate because they typically have minute resolution or coarser, whereas a minute of continuous spraying is too long for misting use. Cary suggests just using a programmable interface card (PIC). There are a number of more complicated solutions involving using X-10 or a direct serial/parallel computer interface. These seem too complicated, so a PIC may be the best solution here. It may be possible to simplify things by using a regular timer attached to a separate timer circuit (so the cheap timer triggers on; the timer circuit makes sure the duration is low).

Possible Designs

One easy proposal from Dan and Joe: start with a Misty Mate air-pump based personal cooling mister. Actuate the valve with a small RC car servo or similar stepper motor; drive this with a PIC. Additional Misty Mate nozzles and valves are available, so if we can find a T-connector for the 1/8" tubing that the Misty Mate pieces mate with, we could add a second nozzle past the valve to get a dual-headed mister.

Pros of the Misty Mate design: air powered water delivery with a battery powered PIC. Very portable and very quiet. The Misty Mate nozzles deliver a very fine spray suitable for dew generation, but it is unclear whether or not it can make it through window screen material. Cons: the water reservoir is relatively small, and the overall unattended continuous run-time is unknown. Cost is medium ($25 Misty Mate, $15 servo, $5 PIC, $10 for extra nozzles, tubing, and any extra materials).

Another suggestion from Dan: hook up a windshield washer pump directly to one or more nozzles, with an inexpensive water reservoir (for example, a 2L bottle). Power the pump with a relay triggered by a PIC. The whole system can be powered by a single 12V or similar AC adapter. Pros: no pumping necessary, and the reservoir is as big as necessary. Very cheap ($10 pump, $10 relay, $5 PIC, $10 tubing, nozzles, reservoir, and miscellania). Cons: the pump may be loud.

Michael's suggestion: use a humidity sensor, like a HIH-3610 Humidity Sensor from Honeywell, hook it up to a transistor or op-amp, and have that drive a relay to operate the pump. This is interesting, but probably impractical because there's some delay between when the spray starts and the relative humidity goes up again; we would need to keep some state to prevent overspraying. It is also expensive ($20 for the sensor alone, although Kyle notes that it's possible Honeywell may send a sample for free). AAG Electronica also sells the TAI8540A 1-Wire Humidity Sensor ($34) which packages the HIH-3610 in a nice digital package.

Other Resources

Jim was wondering how a hygrometer works. Some links:

Indoor orchid growers are some of the most enthusiastic tropical terrarium maintainers... at least one guy has built an orchidarium which includes a windshield washer pump powered mister. Some pictures of his orchidarium are available on-line.

Miscellaneous Notes

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Feel free to use them for any non-profit purpose.

Andrew Ho (andrew@zeuscat.com)