What is GPS - GTPA010 chip + MiniGPS

This blog post is about some experiments done by my friend, Sainath and me with the GPS chip. These experiments were done about 6 months back and this post should have been up at that time only but as the saying goes – it’s better late than never. So read on and explore the GPS.

GTPA010 GPS module

GPS stands for Global Positioning System. It triangulates data from 3 or more satellites and gives the accurate position. This process is called trilateration. GPS has long been used by adventurers, explorers, in cars for navigation, military and at many other places.

As the technology matures, the chips and devices becomes less in size and ultimately can be fitted anywhere on the circuit. So, the aim of these experiments was to explore the GPS chip, put it on a circuit board and place that board on an animal to track its position. This is a classic example of wildlife sensor network.

The GPS satellites which orbit the earth broadcast radio signals which the receiver like GTPA010 catch. Two important data packets that the receiver gets is ephemeris data, used to calculate position of each satellite in orbit and almanac data, which has data about the time and status each satellite. The GPS receiver talks with the computer over serial port using the NMEA protocol.

Circuit setup. The chip uses serial communication.

Now, there are 3 scenarios which could happen when you start the GPS. If the GPS has been off for days, it takes long to get the position and this is called a cold start. In this case, the receiver searches for the satellites and gets the fresh almanac and ephemeris data. It takes usually 15-30 mins to get a fix.

The second is called warm start, when the GPS receiver has the almanac and knows the time but waits for the ephemeris data. It usually takes 1-2 mins to fix.

Finally, if GPS is off for some time only, then it tries to get a fix based on the previous data in memory. This is called hot start and the time to fix is 10-30 secs.

MiniGPS software

Now that I have explained the working of GPS, let us turn our attention to information that we want from the GPS. The information we are looking for is sent in a string called $GPGGA - Global Positioning System Fix Data. This is a part of NMEA. 

The string contains the UTC time, the position in latitude and longitude, and GPS quality indicator (whether GPS got fixed or not). To get a proper view of the satellites and see the signal strength, I used a software called MiniGPS which reads the data from the GPS receiver and beautifully displays it in a chart. A snapshot of the software can be seen. 

The chart will show the position of the satellites. You can select what type of start you want and also there is an option for selecting the baud rate for the serial connection. 

GPS is a wonderful invention and useful in many places. So, I recommend you to try playing with it and make some hobby projects. Happy tinkering :)