I built and tested a GPS receiver with Natalie Be’er for our Wildlife Tracking class. Each team in our class was assigned a different module to test, so that we could compare the reliability and performance of each GPS module.
GR10/MN1010 GPS Module Operating Characteristics
* Typical current is 35 mA, maximum current is 40 mA
* Voltage is 1.8 VDC ± 0.15 VDC
* Serial communications interface, output is TTL Serial, 4800bps
* VCC, ground, and TX line are the minimum connections
* Dimensions: 0.62×1.35″ (16x35mm)
* Weight: less than 0.5oz
* Antenna 2SMD6 with flat rectangular shape should be oriented horizontally face upwards towards the sky
* GR10/MN1010 product source and datasheet on Sparkfun
Here is a photo of the device:
OpenLog Operating Characteristics
* Input voltage from 3.3V to 12V
* 2mA idle, 6mA at maximum recording rate
* Log to low-cost microSD cards up to 16GB, currently supports FAT16 and FAT32 microSD cards
* Configurable baud rates (2400 to 115200bps)
* Power, ground, and RX-I are the minimum connections
* Two LEDs indicate writing status
* OpenLog data logger product source and datasheet on Sparkfun
How to Get Started
Follow these steps to connect the GPS module to the OpenLog device with mini-SD card:
* You need these parts: 5V battery (or 3.7V LiPo battery), GR10/MN1010 GPS module, OpenLog data logger, mini-SD card (we used 2GB), small breadboard, wires, and computer (to read the text file).
* For the GR10/MN1010 GPS module pins, use the VCC for power, GND for ground, and TXO to connect to the OpenLog device.
* For the OpenLog pins, use the VCC for power, GND for ground, and RXI to connect to the GPS module.
* For the battery, red is power, and black is ground.
* Once the circuit is powered, you should see one light blinking on the GPS module, and two lights blinking on the OpenLog device.
Follow these steps to log your GPS data:
* Before you go on your walk, make sure your battery is fully charged. Also make sure the baud rate is 4800 bps in the config.txt file on your SD card.
* Orient your GPS module horizontally face up to get the most accurate readings.
* Talk a walk, gather your data serially onto the SD card.
* When you are finished with your walk, remove power to the circuit and pop out the mini-SD card and plug it into an SD card reader connected to your computer.
Follow these steps to interpret the data:
* Open the text file(s) and use the GR10/MN1010 datasheet to interpret the NMEA serial sentences containing all the GPS data (location, satellites in view, altitude, time, speed, heading, etc)
We went out to Prospect Park in Brooklyn and made a loop around the west side. There were no tall buildings nearby, just wide open spaces and some small trees.
(After testing both mobile apps side-by-side, we found the My Tracks app to be more accurate as it acquired a fixed location faster, and the UI was much simpler to use.)
Initially, we let the GPS receiver sit under the open sky for 5 minutes to acquire satellites. We were receiving NMEA data, but no latitude or longitude readings. Back at the lab, we figured out that we needed to use a 4800 baud rate instead of a 9600 rate, so we knew that we were using the correct command in the config.txt file (4800,8,1,0). Despite everything, the antenna was not strong enough to acquire 3 satellites.
The GPS trackers on our Android phone and iPhone tracked the walk with no problems, and showed a live update of our location. The SparkFun GPS module only picked up 1 satellite throughout the entire walk. There were no errors, and the power lasted through our walk, but our data came back as 0 degrees for both latitude and longitude. We tried both a 3.7v and 9v battery; they powered the OpenLog device without a problem.
Assuming the antenna was too weak, we tried two other GPS modules. Both were the same SparkFun make. Both found 3 satellites, but neither logged longitude or latitude.
However, if you are able to get successful NMEA sentences with accurate longitude and latitude data, use Quantum GIS software (free open-source) to visualize, manage, edit, and compose printable maps. This is what Professor Anthony Di Fiore uses for his monkey tracking. I found a good website called GPS Visualizer that converts your GPS files to kml or kmz data that you can drag onto Google Maps. You can also use GPS Babel, but I don’t think it is not as straight-forward to use as the GPS Visualizer website.
The antenna on this GPS module was too weak to pick up satellites, and then too weak to receive location data. Although it looks like one of the simpler models, it is also one of the weakest.
In terms of ruggedness, the GPS module that we tested has less than 75mW power consumption and can withstand temperature range from -40C to +85C degrees and up to 60,000 feet altitude, so ostensibly it would be a suitable candidate for animal telemetry in the rain forest except for the antenna failures. It is also very lightweight and small form factor with the sleek 3.7 LiPo battery.