Using UART to read GPS module

In this tutorial we’ll cover how to wire up your BeagleBone Black to Adafruit’s Ultimate GPS Breakout (MTK3339) and read GPS locations over the UART serial interface.

Requirements

• Setup Studs
• BeagleBone Black
• Adafruit Ultimate GPS Breakout – $40 from Adafruit

Wiring

Wiring diagram for connecting your BBB to the GPS breakout:

BBB Pin	GPS Breakout Pin
P9_1	GND
P9_7	VIN
P9_24	RX
P9_26	TX

Coding

First create a new project:

$ fan studs init uartgps

Next edit your src/fan/Main.fan to look like:

using studs
using concurrent

const class Main
{
  static Int main()
  {
    // enable UART1
    DeviceTree.enable("BB-UART1")

    // open uart and read forever
    uart := Uart.open("ttyS1", UartConfig {})
    while (true)
    {
      try
      {
        line := uart.in.readLine
        echo("# $line")
      }
      catch (Err err) { err.trace }
    }

    // never get here; but close and return
    uart.close
    return 0
  }
}

Enable UART1

UART1 is disabled by default on the BBB, so the first thing we need todo is enable it using a device tree overlay, which is done with the following code:

// enable UART1
DeviceTree.enable("BB-UART1")

The ttyS1 serial port will now be available for use.

Open port

Next we need to open the UART with the appropriate configuration options. The GPS module happens to use the default config (9600-8n1) so we can pass in the defaults:

uart := Uart.open("ttyS1", UartConfig {})

Read port

In our example code, we will loop forever dumping what we read from the GPS module to stdout:

line := uart.in.readLine
echo("# $line")

The uart.in.readLine will block until data is available and read up to the next CRLF terminator.

Running

To build and run your project:

$ src/build.fan
$ fan studs asm
$ fan studs burn

Insert your SD card and power up your BBB. If you have the serial console connected to your PC you should start seeing the stdout from our application:

# $GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
# $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39
# $GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A
# $GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48
...