wireless sensors for tree growth

[KevinGriffin]

Hi Everyone,
My colleagues and I at Columbia University and the Black Rock Forest Consortium would like to outfit trees with linear displacement sensors to record tree growth. As part of the project we will be developing curricular materials to allow school kids to relate tree growth to environmental conditions.

The sensors have a simple 0-5vdc signal that is related to the change in diameter of the tree. My question for you all is related to collecting these signals and transmitting the data to a project web page were students can “watch trees grow”. Ideally I would collect data every 20 min. I would like to transmit the data to a wireless network in our science center (a few hundred meters away). Alternatively we could collect data on SD cards but would loose the ability to let kids relate the current conditions to the plant biology which is what I think would help make the project come alive.

Is this a job for a trinket? An Arduino? Or some other system?

Thanks for your time

[adafruit_support_rick]

Interesting project!
Pretty much any kind of microcontroller will do what you are asking about. A Trinket is certainly sufficient. More pertinent questions are: what sort of sensor are you thinking about using, how are you planning to power this, and how long do you expect to keep the observations running?

Since you mention using an analog sensor, it's important to know the mechanical situation, so that we know what kind of resolution you need on the analog/digital conversion. Trinket and Arduino have 10-bit ADCs built-in, but my hunch is that the changes may be subtle at times, and so you would want as much resolution as possible. A 16-bit ADC may be a better choice.Do you have a projection for the rates of change you're expecting to see?

You are probably looking at an XBee system for the wireless communications, since a few hundred meters will be too much for WiFi.

[adafruit_support_bill]

I think the sensor will be the tricky part. I'm not a tree expert, but I'm not sure if a growing tree would create an outward force on the sensor or just grow around it. I have seen many trees that have grown around wires rather than push them away. A non-contact solution might be a better choice.

A simple non-contact sensor would be a camera mounted at a fixed location relative to the tree. Any change in diameter could be measured directly in pixels.

[KevinGriffin]

Thanks for the feedback! Yes the change in diameter we are talking about is very very slight so I imagine the 16 bit converter makes more sense, although the current data logger I am using is a 13 bit ADC. The sensor I am currently looking at comes from Midori - LP-10FB-2K ( www.midoriamerica.com). It takes 5vdc, but does not need to be continuously powered.

The set up is to attach the linear motion potentiometer to a carbon fiber plate which is then attached to the tree with 3 stainless steal threaded rods (materials chosen to reduce any thermal expansion). Each of these is drilled into the heartwood of the three so they are anchored and not moving as the tree grows. The plunger of the potentiometer (which is sprung) is appressed to the surface of the tree and moves as three changes diameter.

Research has shown that changes in stem diameter can be detected on a 20min. time scale. As the sun comes up the stem diameter decreases since the water moving through the stem is under tension. Then over the course of weeks and months the total diameter increases as the tree grows.

I hope I can power these with solar and a smallish battery - basically continuously. The longer the sensors run the more valuable the the record becomes.

I really appreciate the feedback!

ELECTRICAL SPECIFICATIONS:

ELECTRICAL STROKE: 10 mm (F.S.)
TOTAL RESISTANCE: 0.1, 0.2, 0.5, 1, 2 kOHMS
TOTAL RESIS. TOLERANCE: ±20%
LINEARITY (INDEPENDENT): ±1% (±0.5% AVAILABLE)
REPEATABILITY: 0.03%

POWER RATING: 0.3 WATTS @70°C

INSULATION RESISTANCE: 500 meg OHMS MIN. @ 500 Vdc
Dielectric Strength: 500 Vrms, 50/60Hz, FOR 1MINUTE
RESISTANCE TEMP. COEFFECIENT: 400 ppm/°C

[adafruit_support_rick]

You can sleep the entire system during the 20-minute measurement intervals, not just the sensor..

[barrypineapple]

Hi..I'm new to this forum and a beginner with arduino, but wonder whether you might consider using an lvdt...As an ex plant physiologist I used one of these for precise measurement way back when attached to a BANNED to measure depth of penetration into living plant cells... they are not particularly cheap, but I suspect way way more accurate than the device you are considering...For what it's worth I've seen people demonstrating diy versions on the internet too...If you haven't already started...might be worth a look...You would best consult others on the best way to use one with an arduino though...If I recall, the one I used had the necessary electronics built in and a fixed low volt dc in gave variable dc out that in those days we monitored with a chart recorder, but should be far easier now

also maybe http://www.microstrain.com/wireless/dvr ... wwodhTYARA possibly a useful link (I haven't done an exhaustive search)

good luck..pete