Turtle Sense/Phase Two
Phase two is starting up.
People
- User:Dave -- Electrical engineering / Mechanical engineering
- User:Sam -- Project manager / Embedded Software
- User:Tom -- Engineering support
- User:Eric -- Fundraising / Community liaison
- User:Chuck -- Sea Turtle community outreach / Materials
- User:Chris -- Web Server Admin
- User:Mark -- Web Application Development
- User:Britta -- National Park Service Biologist
Overview
When nests are discovered by park personnel, the nests are uncovered, the eggs counted, and a DNA sample is taken. At that time, a smart sensor the size of a turtle egg will be placed on top of the turtle nest before the excavated sand is filled back in to cover the site. The smart sensor will measure motion and temperature in the nest, with the hope of being able to determine when hatching is imminent. The smart sensor is connected to a communications tower which will send out regular reports on the activity in the nest using M2M technology. The text file reports are FTP'd to a website directly from the communications tower. The plan for Phase Two is to create about 10 communications towers and 20 smart sensors for installation in the Outer Banks of North Carolina during the Spring and Summer of 2014. Data will be collected from up to 40 nests, and the data will be analyzed as it is collected to attempt to predict imminent hatching.
Smart Sensor
The Smart Sensor has a 3-axis motion sensor (accelerometer) and temperature sensor connected to a very low power microprocessor. There is also an RS485 transceiver chip which connects to the communications tower via a shielded Cat5 cable. The smart sensor can be programmed to take readings 12.5, 25, 50, 100, 200 or 400 times every second. Each reading is compared with the previous reading to determine the change in acceleration -- or "jolt". Rather than record each jolt, the sensor counts how many readings have reached approximately 25 different magnitude levels. These magnitude levels (which we call "bins counters") are in a logarithmic scale. Each bin is the square root of 2 larger than the previous one. We keep count for a variable amount of time (between 1 and 6 minutes) and then start a new set record with a new set of bins. This allows us to track how much motion there was at multiple magnitudes over time.
Communications Tower
Since it is not possible to make telemetry connections under wet salty sand, the smart sensors are connected to a communications tower. The design is based around creating a custom processing mother board connected to an off-the-shelf telemetry board. The mother board has a very low power microprocessor which controls and monitors the activity of the smart sensor and controls the telemetry board. There is also a power supply, a RS485 telemetry chip and connectors for future expansion. The electronics are mounted inside a 3 inch PVC pipe and fittings anchored in a 5 gallon bucket filled with concrete. The concrete base and Cat 5 cable are buried in the sand. The The tower sends text reports to our web space via an FTP connection using the telemetry board once a day when the nests are not very active, and increases to 6 times a day when the nest becomes more active. Since the communications tower only makes one to 6 reports a day, The microprocessor turns the telemetry board on and off, so that it consumes no power when it is not being used.
Hand-Held Registration Unit
A communications unit is mounted in a small hand-held unit so that it can be taken in the field when nests are excavated. This allows park service personnel to carry just the light-weight sensors and the hand-held unit to the nest sites. Later, the heavy communications towers can be brought in. The Hand-Held units have GPS capability. They are programmed to test the sensors to make sure they are functioning properly, get a GPS reading, check for a good cell connection, and get the local time and date from the cell phone network. The date, time and GPS location are sent to the sensor, so that all this information will be available to the communications tower when it eventually connected.
Web design and Database
All reports are uploaded to our web-space. The reports are comma separated text files with headings and labels, so they can be read by people and computers. We are beginning work on a database to store all the data. When reports are uploaded, the communications units also check the webspace for a new parameter file and download it if it is found. The parameter file has settings that effect the behavior of the devices. Here are some of the things that can be changed:
- The frequency of reporting during inactive days
- The frequency of reporting during active days
- The number of inactive days
- The number of records per report
- How frequently samples are read by the sensor (12.5, 25, 50,100, 200 or 400 times per second)
- All of the other settings possible for the sensor
- Whether reports are verbose (labels on all the fields) or just data
- Whether temperatures are calibrated
Engineering
Commercial options
Before proceeding, we researched other commercially available data recording systems to see if anything that would meet our requirements was available. None of the options we found were low enough power to fit our needs, and none provided the data we were hoping to collect. The closest matches we found would have required as much or almost as much custom engineering on our part to make it work, and there was no cost benefit to going that route.
Components
Turtle egg sensor
The Phase One design used plastic ping-pong balls (not good ping-pong balls, but cheap plastic knock offs) and a temperature/motion sensor pre-installed on a small circuit board (Qty 1 Price=$14.95). Assembly involved cutting a small slot in a ball, putting in some silicone caulk, inserting a sensor board attached to a cable into the caulk, and then filling the rest of the ball with caulk. A ball cut in half covered the slot and makes a thorough seal with the silicone. This design was abandoned for several reasons. The silicone did not fully set, even after a few months in the field. The sensor was unreliable, which may have been because it was connected directly to the microprocessor via the long Cat 5 cable and communications were using a very slow bit-banged SPI connection. To make the
Mother board
Telemetry board
We are using plug in Terminus boards made by Janus. One board works with AT&T, T-mobile and many international GSM networks. Another works with Verizon. The boards are interchangeable so both will plug into our motherboard. The cost is roughly $140 qty 1 and are from the manufacturer, Janus. Janus is generously offering us a discount on their boards.
Other components
The only other components necessary are the cable and connector for the turtle egg sensor (a few bucks), two antennas for the telemetry board (GSM and GPS), which cost about $20 (perhaps more if reception is a problem). The units should operate for roughly 4 months running on 4 or 8 low self-discharge NiMH Batteries. The batteries and holder (TBD) cost about $25. Also, anyone creating these devices will need the hardware necessary for programming the microprocessor (more about this later).
The hardware cost of the electronics is about $250 per unit after start up expenses, and not counting telephony charges, taxes and shipping.
Parts list
Schematics and System design
- Block Diagram of System
- Smart Sensor PCB 0.24
- Communicatins PCB 0.25a
- Circuit Description for Turtle Sense v.0.25a
- Circuit Description for Smart Sensor v.0.24