NMEA Data consists of human unreadable characters

Owned by Kim Jansen (Unlicensed)
Last updated: Aug 06, 2019 by Jeroen van Onzen | Oculus Technologies (Unlicensed)
2 min read

Problem

Collector does not show data updates, a serial monitor tool shows only human unreadable characters.

There is a large deviation from the expected clean NMEA0183 message format (eg. "$GPGLL,4916.45,N,12311.12,W,225444,A,*1D")

Example (Putty):

Solution

Steps that likely resolve this issue.

Make sure to check from source (eg. bridge) to destination (COM-port in Collector):

  1. Baudrate settings are correct
  2. Signal levels match
  3. Polarity of signals correspond
  4. Cables used

Please note:

  • Putty is your friend, please use this tool often (every change you make) and take notion of changes in what is displayed
  • Most commonly used baudrates are: 4800bd, 9600bd and 38400bd, however others numbers (19200, 76800, 115200) are possible. 
  • RS232 signals have a specified maximum cable length of 12 meters and are susceptible to interference: use RS422 or MOXA NPort 5x50 instead
  • RS232 can be connected directly to our unit on pins 2 (RxD) and 5 (GND) of the sub-D 9 connector on the rear
  • RS422 can be connected to a MOXA NPort, Shipmodul MiniPlex or RS422 to RS232 converter. You could connect directly a RS422 (RxD- / RxD+)  to a RS232 (pins 2+5)
  • A swap of wires/polarity of Rx and GND pins (RS232) or RxD- and RxD+ pins (RS422) may resolve the issue even though your information about polarity indicates the opposite
  • All cables must be properly shielded and at least one end of a cable must be connected to ground or GND, grounding both ends may lead to a earth-fault. The best method to verify this is to connect the cable to a laptop. If this is working, a grounding issue could be feasible. Using a UPS or optical isolator could solve this issue.
  • A Multimeter can be connected to wires for a coarse check whether data is being send: set to DC the voltage should jump frequently between max. -25V and +25V (RS232) or max. -10V and +10V (RS422)
  • The 'sending' equipment will have wires connected to pins indicated with Tx, where the 'receiving' equipment will have the wires connected to pins indicated with Rx; on the unit Tx-wire connects to Rx-pin

Suggested tools:

  • Laptop with a good quality serial to USB converter (eg. MOXA UPort 1150) and Putty 
  • Multimeter
  • Screwdrivers and pliers
  • Test leads and sub-D connectors

Image result for laptopImage result for fluke multimeter


In case this does not resolve your issue, please have a look at related issues or contact our office.