More Yaesu VX-8 GPS implementation details.

4Z7DTF left a comment on my post "Another Yaesu VX-8DR external GPS with an Arduino/..." to let me know about his VX-8 Arduino GPS project on github.

There have been a number of projects that use either an Arduino or bare ATtmega microcontroller to turn the GPS module's NMEA sentences back into the a format the brain dead parser built into the VX-8's firmware can handle.

He has done some additional testing, actually fuzzing, showing the VX-8's parser does no error checking what so ever. 

Also, another interesting bit, in his work, he noted there is no need for the communication to be bi-directional. I don't know what, if anything the VX-8 tries to send to the GPS module, but it appears to be unnecessary. 

What is interesting about that is the microcontroller then really only needs a single serial port.  Most of the other projects are bi-directional using a software UART emulation for the second port.   So it might be possible to implement this project with something much smaller and even lower power.   It would be interesting to see if this can be done with the ATTiny85, using something like the Adafruit 3.3V trinket.  That is supposed to draw around 9 milliAmps at 8 Mhz, but 3 mA of that is just for the green power LED!  The ATTiny has no built in UART, so it would be all software serial. 

Another Yaesu VX-8DR external GPS with an Arduino/ATmega328 translator.

I've collected links for a few of these projects to add a better external GPS to the Yaesu VX-8DR, instead of the somewhat proprietary Yaesu option.

Here's another one from VK3YY that got posted recently:

• https://vk3yy.wordpress.com/2015/07/24/vx-8dr-and-gps/ 

Here's code from DFannin on github:

• Arduino code for buidling Yaesu VX8r Handheld Transmitter-compatible GPS

Update 2016-01-15, 4Z7DTF notified me about his project, which includes more additional analysis of how poor the VX-8's parsing and error handling is.

•  4Z7DTF's VX-8 Arduino GPS interface on github 

Background Info:

Good detailed blog post Reverse Engineering the Yaesu VX-8DR GPS Interface. From Feb. 2013. He didn't arrive at the solution, which I believe F4FXL and at least one other have. But I think he's got most of the relevant details for the padding differences listed as well as some other very useful info including details on the GPS chips used in VX-8 and VX-8G.

We now know how to connect to and send a properly formatted GPS NMEA message to the Yaesu VX-8DR. Here's the summary:

• 9600baud TTL 3.3V serial signalling, 8/N/1
  • NOT RS232 -5 to +5V signalling -- you need a level converter if that's all you have
• 3-wire physical interface to the following pins:
  

  Pin	GPS Side Purpose	Yaesu Side Purpose
  4	GPS RX	Yaesu TX
  5	GPS TX	Yaesu RX
  6	GPS GND	Yaesu GND

• According to 4Z7DTF (2016-01-15), there is no need for the communication to be bidirectional. Only the TX Data from the GPS to the VX-8 is required.

The messages need to be formatted exactly as follows: Message Type Source Sentence $GPGGA Sample $GPGGA,123223.000,4131.2334,N,00021.1216,E,1,04,02.7,00123.4,M,0051.7,M,000.0,0000*41 Syntax $GPGGA,hhmmss.sss,llll.llll,a,yyyyy.yyyy,a,x,xx,xx.x,xxxxx.x,M,xxxx.x,M,xxx.x,xxxx*hh $GPRMC Sample $GPRMC,123223.000,A,4131.2334,N,00021.1216,E,0000.00,291.33,301011,,*3E Syntax $GPRMC,hhmmss.sss,A,llll.llll,a,yyyyy.yyyy,a,xxxx.xx,xxx.xx,xxxxxx,,*hh $GPZDA Sample $GPZDA,123223.000,30,10,2011,,*55 Syntax $GPZDA,hhmmss.sss,xx,xx,xxxx,,*hh