16 Jan

Even Plants are Tweeting Nowadays


As part of our display at the Fairmount Water Works, one our plants will now be tweeting when it needs to be watered. (First the teenagers, now the plants?)

This setup uses an Arduino Uno ($25), a WiFi shield ($80), and a Vegetronix VH400 soil moisture sensor ($37). This WiFi shield has an integrated antenna, which allows us to connect to the wifi at the Water Works and send tweets over its network.

We didn’t want our plant to be someone who only talks to you when they need something, so we have a series of different tweets:

  • “Water me please!” when the moisture value falls below 250.
  • “URGENT! Water me!” when the moisture value falls below 150.
  • “Thank you for watering me!” when there is a change in moisture level of at least 100 and the new moisture value is above 250.
  • “You didn’t water me enough!” when there is a change in moisture level of at least 100 and the new moisture value is below 250.
  • “You overwatered me!” when the moisture level climbs to above 400.

One problem we ran into was that Twitter doesn’t allow repeated tweets, as a way to block spam.  Because of this, we had to add more content to our tweets.  In addition to the text, each tweet displays the moisture level and the tweet number (we added a tweet counter in our code).

You can see our plant’s tweets here.

View the code after the jump.

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05 Jan

Bigger, Better and Brighter LED Display

IMG_6699 IMG_6696

Our previous post detailed the simple soil moisture sensor with an LCD display that has been keeping track of our plant’s watering needs at the Fairmount Water Works.  We decided the project could use a little more flair—plus, our original LCD display got a little wet.  Luckily, our new 16×32 LED Matrix has its own waterproof case. The setup uses an Arduino Uno ($25), a Grove base shield ($10), a Vegetronix VH400 soil moisture sensor ($37), and a 16×32 RBG LED matrix panel ($25). All of the electronics are safely tucked into a waterproof Pelican case.

We decided to display more information with our LED matrix.  Now, it will display the words “Water me!” when the soil moisture level falls below a voltage of 1.2, or “Don’t Water” when the moisture level is greater than 1.2 V. It then displays the voltage, followed by “Water Works,” and repeats.

We found that with RGB (red-blue-green) matrices like this one, certain colors require more power.  When using solely the power coming through the computer to the Arduino to power the matrix, we were limited to basic red, blue, and green colors.  Any other colors would be displayed as one of the tree.

We decided this was a little too boring, and experimented with supplying power from the wall directly to the matrix, in addition to the power coming from the wall to Arduino.  This got us very bright, vibrant colors. However, the LEDs were glitchy and flashing.  We think the matrix was getting just a little too much power, and it was distracting.  In the end, we stuck with the additional wall power, but used lower power colors.  This gave us the brightness we wanted, without all the flashing.

View the code after the jump.

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08 Dec

Fairmount Water Works Sensor

Now on display at the Fairmount Water Works—a simple soil moisture sensor with an LCD display to keep track of a plant’s watering needs. This is just a first step in developing some really interesting ways to monitor plants and get feedback on plant health. Working with two 10th grade students at Science Leadership Academy, we’ll be investigating how to use visuals, audio, and Twitter to communicate environmental data.  (We’ll also be investigating why we didn’t put the electronics in a waterproof case, because what’s more awesome than an unprotected circuit board next to a plant that’s being watered?)

This setup uses an Arduino Uno ($25), a Grove base shield ($10), a Grove LCD display ($14) and a Vegetronix VH400 soil moisture sensor ($37, though you can find soil moisture sensors for under $10; we like the performance of the VH400). The Grove shield stacks on top of the Arduino and lets you use snap-in wires to connect sensors and displays. The Arduino code is after the jump; it’s basically modified code from the Grove website.

We did a rudimentary calibration of the soil moisture sensor and got readings for the sensor in air, in dry soil, in wet soil, and immersed in water. From those measurements, we estimated readings below 200 would probably indicate the plant needs watering. It’s not an exact science, but we’ll learn more about what the sensor output means as we go along.

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12 Jun

Fourth Installation: SLA Beeber


Students at Science Leadership Academy’s Beeber campus installed Root Kit #4 yesterday, capping off an 8-week minicourse of designing and building the sensor housing, soldering the kit’s circuit board, testing radio signal strength, and troubleshooting along the way. Remember the waterlogged sensors from a few posts ago? We did an immersion test and found out water was leaking into the Pelican case at the base of the cable glands:


We used a combination of Rust-oleum Leak Seal spray (not that effective, smells toxic) and silicone caulk (it works, but it’s messy-looking) to waterproof the case. After connecting to the school’s network and testing signal strength from the flowerbed to the 3rd floor office, students buried the soil sensors:


The students went with the eyeball housing for their site, and designated the rocketship design for a future installation at the Franklin Institute this summer (details to come). We poked a pinhole into the eye’s center to allow the antenna to peek out:


Thank you to all the SLA students, Mr. Sokoloff, Darya Drahun and Sandy Sorlien—mission accomplished!

08 May

Seeing Daylight


Week 3 at SLA Beeber: Some nice weather made the thought of soldering circuit boards and decorating sensor housings in the classroom unappealing. We jailbreaked to nearby Indian Creek in Morris Park. The west branch of the creek was recently daylighted—the creek had been buried in a sewer in 1928, and the Philadelphia Water Department and the U.S. Army Corps of Engineers recently completed the process of bringing the creek back aboveground. Approximately 750 feet of new stream bed was constructed, and 1,300 feet of stream channel was reconfigured. In the photo above, you can see how the new stream features riffles and pools that serve as habitat for fish and aquatic invertebrates. A blog post at phillywatersheds.org has more detail.

02 May

Eyeballs and Circuits


Week 2 at Science Leadership Academy’s Beeber campus saw the students begin constructing two aspects of the Root Kit: the circuit board (a JeeNode, which is a low-cost, low-power microcontroller with a radio transceiver) that controls the sensors, and the artistic housing that will cover the Root Kit outside in the garden. One group of students soldered while the other group painted.


We followed JeeLabs’ excellent step-by-step instructions to solder the microcontroller boards. The students are charged with creating their own do-it-yourself manual for creating Root Kits, and their main tips for soldering were 1) Keep track of how long the solder wire is—too long and you don’t have much control, too short and you increase the risk of burning yourself; and 2) Soldering gets easier as you go along. Definitely good advice.


The students also got to work on their two housing designs: an eyeball (above), and a crashed rocketship. The eyeball came together quickly: acrylic paint, some glitter glue, and a plastic bowl. It looks excellent—I hadn’t considered how these designs need to be bold and simple; they should be apparent amid garden vegetation from a third-floor classroom window 100 feet away. The eyeball achieves that. More on the rocketship design next week, as we didn’t have quite the right cutting tools for the plastic fins. Student tip for working with recycled 2-liter soda bottles: Use a base coat of white paint first, then put a color coat (in our case, silver) over top of it. The first coat doesn’t adhere well to the bottle’s plastic.

A word of advice for procuring housing materials: Dollar stores are your friend when you can’t find recycled plastics that fit your design needs. Ideally, we’d use recycled materials 100% of the time, but sometimes exceptions are made. Just make those exceptions as cheaply as possible.

24 Apr

Design Day at SLA


Yeah, that does say “duck butt” on the whiteboard. It’s a long story. At Science Leadership Academy’s Beeber campus, a 9th grade class is becoming a company. Its product is the Root Kit, and over the next 8 weeks the students will be responsible for building the kits, soldering the circuit boards, designing the housing, building the housing, installing the sensors, troubleshooting the kit, and creating a do-it-yourself construction manual for other schools. Is that too much to ask?

Yesterday, the SLA Beeber students did some rapid idea generation (I can’t stand the word “brainstorming”) to come up with concepts for the Root Kit housing. Factors to consider: This will be out in a garden, so it has to stand up to the elements; it doesn’t have to be waterproof, but it can’t be made of cardboard and paper, either. Using recycled materials whenever possible is good. And it can’t be made of metal—the radio signal from the Root Kit doesn’t carry well when the antenna is enclosed in metal.


Look back at the top picture and you can see that, based on the distribution of Post-It notes on the whiteboard (a Post-It indicates a student liked an idea), there was little consensus. None at all, in fact. Not even a hint of it. At the end of the day, we narrowed it down to two designs (an eye and a crashed rocketship) based on … I’m not sure, exactly. Buildability was one factor; the garden gnome was a great idea, for example, but we lack the sculpting skills to make it happen at the moment. Also, SLA Beeber’s mascot is a rocket, so that design seemed apt. It’s buildable, too, perhaps using two recycled 2-liter soda bottles.

19 Mar

Root Kit Construction


With the installation of sensors at four Philadelphia schools about a month away, it was time to build some additional Root Kits. Version 1.0 is housed in a Pelican 1010, a $10 waterproof case normally used for stashing your cell phone during whitewater rafting trips or something. We used a half-inch drill bit to drill out the three holes for the soil moisture sensor cables, and the cables are secured to the case with PG7 cable glands (about $3 for a pack of 10) that you can tighten by hand.

A few words about drilling: This was a two-person job; one person steadying the left side of the case and the other drilling, slowly and with constant pressure, the three holes. At first, we experimented with drilling pilot holes with smaller bits and moving up to the half-inch bit, but by the end we just did the job with the half-inch bit from start to finish. (We haven’t yet cracked the plastic on the Pelican cases, but have definitely destroyed a variety of less-sturdy plastic components while drilling.) It was difficult to align the holes and make it look pretty. The drill bit walks. This is not of great concern, however, since these cases will eventually be covered by students’ creative and artistic designs.

Speaking of which, students at Greenfield, Nebinger, and Cook-Wissahickon elementary schools are currently designing Root Kit housings for the design competition. The deadline for submissions is April 4, and more info and downloadable packets and drawing templates are here.

We’re in the process of assembling a complete set of instructions for assembling the Root Kit and plan to work with students at Science Leadership Academy’s Beeber campus this spring to be the first large-scale manufacturers of these sensor kits.