I remember the first GPS unit I bought was a USB device with a sirf3 chip (20 channels, 1 Hz) and it costed around $45. Now I can buy an Ublox NEO-6M under $20 and get much more (50 channels, 5 Hz and other good stuff).
So let’s see how to test these inexpensive but quite powerful units with the help of a Bus Pirate 3.6. First, connect the bus pirate with the GPS unit:
- GND to GND
- 3V3 of bus pirate with VCC of GPS
- MISO of bus pirate with TX of GPS
- MOSI of bus pirate with RX of GPS
Now it’s time to start a serial terminal like Termite and set the correct port number and baud rate (115200 bps). Next, let’s issue the following commands pressing enter after each one:
- m (set mode)
- 3 (select UART)
- 5 (baud rate: 9600, this is the default baudrate of the GPS unit)
- ENTER four times (set data bits, parity, stop bits, polarity, output type to default)
- W (power supply on, the 3V3 pin gets 3.3 volts)
- (1) (run macro #1 which is UART bridge, the Bus Pirate will act as a bridge until reset)
After finishing these steps you should start receiving raw NMEA messages from the GPS unit.
That huge number of commas after each other shows us that this unit knows nothing yet, this was its first (cold) start. Let’s go outside and see what happens.
This looks much better, but it is still hard to understand for a human being so let’s try something else. Let’s download u-center for Windows from here. This is an evaluation software from the manufacturer of the chip. During installation we must make sure not to install any drivers as we are already using the FTDI drivers with the Bus Pirate.
After installing and starting the application a rather empty window greets us.
Using the icons on the left select the correct COM port (COM4 in my case) and baud rate. Now don’t forget: you need to use baud rate of the Bus Pirate and not the GPS since we are using a bridge. So select 115200 and if everything goes well, something like this will happen:
Now we have many-many possibilities to go on with but I won’t cover these (maybe in a later post…). Thankfully, the user guide of u-center is quite detailed so I would start exploring there.
One thing I really wanted to do is to change the baud rate of the unit but somehow I couldn’t manage to do it. Whenever I try to change it to 115200 it gets back at 9600 before I could send a “save configuration” command. I am following chapter 6.1 from the user guide.
If anyone has an idea what am I missing, please leave a comment. Thank you!
Product name: Ublox NEO-6M GPS Module w/ EEPROM – Blue + Green
- Comes with backup battery and antenna, nothing additional needed
- Standard UART
- Antenna comes on a separate PCB, this makes it a bit fragile