GPS-to-Serial

What is it for?

This application is currently used in Liberty-Way project

You can create your own GPS robot without purchasing an additional GPS receiver 🙂

Overview

Simple application for sending phone's GPS coordinates via USB serial port. A USB-UART converter is connected to the phone via USB-OTG. On the phone, you need to press the CONNECT AND START button, confirm the permissions (after confirming the permissions, you need to press the button again) and after that the phone will start receiving GPS coordinates with an interval of 1 second. Latitude, longitude and accuracy are displayed as text on the layout. Each time new coordinates are received, they are packed into an 11 byte packet and sent to the serial port at the baud rate you specified before pressing the button. To stop receiving GPS coordinates and close the serial port, press the STOP button.

Serial packet structure

The packet consists of 11 bytes. At the beginning of the packet, 4 bytes are assigned to latitude, 4 to longitude. Then 1 byte of the XOR check-sum (XOR check-sum is calculated using 8 bytes of latitude and longitude), at the end 2 bytes of the packet ending: 0xEE and 0xEF.

Latitude and longitude values are signed integers. 6 decimal places (from degrees) are converted to 6 integer digits. (-90000000 to 90000000 for latitude and -180000000 to 180000000 for longitude). To get back the degrees of the float type, signed integers must be divided by 1000000.

Latitude and longitude bytes are in Big-endian order.

Packet structure:

byte 0-3: latitude bytes in big-endian order (-90000000 to 90000000)
byte 4-7: longitude bytes in big-endian order (-180000000 to 180000000)
byte 8: XOR check-sum of 0-7 bytes
byte 9: 0xEE
byte 10: 0xEF

Serial packet example:

Serial packet example for latitude: 40.689249 and longitude: -74.044500

Latitude: 40.689249 -> 40689249 -> 02 6C DE 61
Longitude: -74.044500 -> -74044500 -> FB 96 2B AC
XOR check-sum: 02 XOR 6C XOR DE XOR 61 XOR FB XOR 96 XOR 2B XOR AC -> 3B
Packet ending: EE EF

Result:

(HEX) 02 6C DE 61 FB 96 2B AC 3B EE EF
(DEC) 2 108 222 97 251 150 43 172 59 238 239
(BIN) 00000010 01101100 11011110 01100001 11111011 10010110 00101011 10101100 00111011 11101110 11101111

Credits

The app uses the usb-serial-for-android library.