Mysteriously, the sensors at Nebinger and Cook-Wissahickon elementary schools stopped transmitting data late last week. A trip out to each school’s garden quickly revealed the problem: waterlogged Root Kits, with circuit boards and battery cases floating in water. Weren’t these things supposed to be waterproofed? Not against last week’s heavy rain, apparently. We have a hunch as to where the water is getting in; students at SLA Beeber will conduct an immersion test (i.e., put the case in a bucket of water) to see where the water is leaking in and recommend fixes. But for now, the Root Kits are sidelined and drying out, and we’ll test the circuit boards to see if they still work. Check out the futility of the dessicant pack in the photo below:
Last week, judges met at the Fairmount Water Works to view the submissions for the greenSTEM Challenge, a student design competition to create artistic, original housings for the sensors set to be installed at three Philadelphia schools later this month. Competition was fierce—the student team at Greenfield who submitted the zombie head design deserves an honorable mention—but we selected three winning designs: a sword in the stone (Greenfield), a spider (Nebinger), and a futuristic light-up dome (Cook-Wissahickon). The winners are below; the next step is to gather the students for a day of building.
Greenfield Elementary: Zoe, Alexei, Jordan
Over the device we will put a block of foam that hardens for more durability. We will make a sword handle out of water bottles filled with paper and pipes. We will spray orange, brown, and silver paint on the pipes. We will also spray paint the foam silver. The end result will be an homage to the classic story of King Arthur. The wires will come out of the foam. The device will be obscured in a nice cover that complements the color of its surroundings and the storytelling we grew up with. The foam will be covered in dirt and rocks to blend in with the ground.
Nebinger Elementary: Amir
My project is a tarantula. I will have the device inside a Pelican 1010 casing with straws. I will put the wires inside the straws and have the other end connected to the head of the tarantula. I made it easy for you to figure it out in these pictures.
Cook-Wissahickon Elementary: Jonathan, Jhalil, Sean
We will have a plastic dome around the data-sending unit with LED lights inside the top of the dome. We will use battery packs to power the LED lights [to indicate] when it needs to be watered. We will use a circuit board to turn on the LED lights because it will be hooked up to the sensors.
Congratulations to the students! And thank you to the judges: Beth Miller (Community Design Collaborative), Alex Gilliam (Public Workshop), Lisa Wool (Partnership for the Delaware Estuary) Ellen Freedman Schultz (Fairmount Water Works), and Tiffany Ledesma-Groll and Jay Cruz (Philadelphia Water Department).
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.
Went back to Nebinger Elementary to check on the snake sensor described in the previous post, and … the batteries were dead. We got about three days’ worth of good data (see chart, above), taking soil moisture and temperature readings every 30 minutes. There was no rain during that period, but it’s clear from the chart when volunteer gardeners went out and watered the vegetable garden—the temperature (blue line) dips as the cold water contacts the temperature sensor, and the soil moisture (red line) increases. (The sensors were not calibrated, by the way, so pay no attention to the numbers on the soil moisture axis; the volumetric water content would not be at all accurate.)
What happened? The Arduino was programmed to go to sleep between sensor readings, using the functions in the Narcoleptic library. The LEDs and sensors shouldn’t be drawing much from the batteries. There were some hot days in that stretch, but it’s cold weather you have to worry about when considering temperature effects on battery drain. Something else is going on.
Here’s where we dusted off the multimeter and made a somewhat surprising discovery. After wiring a circuit to measure current draw, we saw that the Arduino Uno was drawing around 50 mA (milliamps), even while it was idle in sleep mode. I’m no electrical engineer, and this is probably some fuzzy math I’m about to do, but let’s say a AA battery has 2000 mAh (milliamp hours), and the four AAs are wired in series, so current is not additive. (Read this if I just lost you.) So 2000 mAh divided by 50 mA—we can expect about 40 hours of operation; a little less than 3 days. That’s just about what we got with the snake sensor.
Clearly we need a better approach to conserve battery life—a different circuit, a way to minimize the current draw by eliminating the Arduino’s “on” LED or voltage regulator, maybe even look at different microcontroller boards that don’t consume as much power.
This summer, the playground at Nebinger Elementary School in Bella Vista will lose some impermeable asphalt and gain a rain garden and some porous play surface. It’s all part of a plan to capture stormwater and protect our rivers and streams. But after construction is finished and the vegetation is planted, students may not even realize the function of the system in place.
Thanks to an engaged principal, faculty and educators from the Fairmount Water Works Interpretive Center, however, students are already learning about water-related issues and getting ready for a greener play area (the school already has a very productive vegetable garden in raised planter beds). When teacher Rachel Odoroff was looking for a year-end project for her 7th and 8th grade science classes, we saw an opportunity to introduce some of our work with sensors into the classroom.
The challenge: In two days, work with the students to design and install some sensors to monitor the vegetable garden.
The plan: Well, it’s a bit too ambitious to try to access the school’s WiFi network and get the Solar Sunflower server to display the data, so we decided to make a datalogger to record soil moisture and temperature in the garden. We gave the students a short introduction to the electronics, and they got started with designing the housing. The result? A snake made out of a tupperware container for the head, and pieces of flexible plastic plumbing connectors (the kind you might use to connect pipes under your sink).
Below is the “head” of the snake: an Arduino, an SD card shield (data is written to an SD card, like the memory card in your phone or camera), a battery pack with 4 AAs, and red LED “eyes” that light up when the soil is too dry. The temperature sensor is a black wire that protrudes from the front of the head, like a tongue.
Here is the head of the snake in the garden, placed among some tomato plants:
The tail of the snake—the soil moisture sensor‘s wire threads through the tubing and the sensor is buried about four inches in the ground:
Unfortunately the end of school means the students won’t have an opportunity to examine much of the data, but we’ll be back during the summer to check on the snake every once in a while. We hope to build on this project next year—add wireless communication, upload data to the web in real time, add a light display—and extend it to monitor the rain garden. Thanks to Ms. Odoroff, her students, Drexel co-op Tommy Thompson, and Fairmount Water Works education and outreach coordinator Ellen Schultz for making this project happen. Thanks to PWD engineer Stephen White for coming up with the phrase “snakes on a playground.”
Now that we have the idea of a solar-powered, sensor-equipped sunflower that allows students to monitor plants in a rain garden, it’s time to think about where that sunflower will take root. Greenfield Elementary School in Center City has been a model of a “green school”: In 2009, the Philadelphia Water Department worked with the school’s parent group, the Philadelphia School District, the Community Design Collaborative and the EPA to transform an asphalt schoolyard/parking lot into an attractive, green playground (pictured above) that manages stormwater using rain gardens and porous play surfaces. Watch the video below for more detail:
A similar transformation is about to take place at Nebinger Elementary School in South Philadelphia (actually, Bella Vista—you can start a small war in Philly if you’re not careful about getting the neighborhood correct). This summer, construction begins at Nebinger to create a rain garden and porous play surface where asphalt used to be. The rendering below shows what the greened schoolyard might look like. The rendering below also shows what it might look like if a child with one foot were running—you see that guy in the background?
Schools are great locations for green infrastructure. Blacktop schoolyards tend to be large impervious spaces that normally contribute a large volume of stormwater to the sewer system. Schoolyard makeovers can revitalize play areas and introduce nature to the urban landscape. Having the students use technology to monitor their vegetation adds another layer of connectivity and offers even more opportunity for STEM education.