Checksums on incoming NMEA strings

[abarrow]

Well, that was fun! Thanks for the help. It looks like I have something that works. 

I'll know when I get a chance to take it down to the boat, but using simulated strings in Node-Red is works great!

Here's the code:

Code:

[{"id":"def155ce.cb8dc8","type":"tab","label":"Flow 2"},{"id":"4fc0cc12.46de24","type":"switch","z":"def155ce.cb8dc8","name":"Filter just DBT and HDM","property":"payload","propertyType":"msg","rules":[{"t":"regex","v":"^(?=.*IIDBT)","vt":"str","case":false},{"t":"regex","v":"^(?=.*IIHDM)","vt":"str","case":false}],"checkall":"true","outputs":2,"x":443.99993896484375,"y":367.99993896484375,"wires":[["d06bc454.854278"],["142750e6.16540f"]]},{"id":"de39de6.89c9d2","type":"function","z":"def155ce.cb8dc8","name":"calc checksum","func":"var nmea = msg.payload;\nvar checksum = 0; \n\nfor(var i = 0; i < nmea.length; i++) { \n  checksum = checksum ^ nmea.charCodeAt(i); \n}\nchecksum = checksum.toString(16);    //convert to hex\nnmea = '$' + nmea + '*' + checksum;  //make the full nmea sentence again\n\nmessage = 'Full message =' + nmea + '\\r\\n' + 'Checksum = ' + checksum ;\n\nmsg.payload = nmea;\nmsg.payload = msg.payload+\"\\r\\n\";\n\nvar msg1 = {\n     payload: msg.payload\n };\n return msg1;","outputs":1,"noerr":0,"x":1018,"y":423,"wires":[["6fe378e5.112f58","bc1148e9.02e848"]]},{"id":"142750e6.16540f","type":"function","z":"def155ce.cb8dc8","name":"Strip front and back","func":"var nmeaFull=msg.payload;\n\n    \nvar nmeaStripped=nmeaFull.substring(1, 99)\n\nmsg.payload = nmeaStripped;\nreturn msg;","outputs":1,"noerr":0,"x":802.0000610351562,"y":423,"wires":[["de39de6.89c9d2"]]},{"id":"6fe378e5.112f58","type":"udp out","z":"def155ce.cb8dc8","name":"","addr":"127.0.0.1","iface":"","port":"10108","ipv":"udp4","outport":"","base64":false,"multicast":"false","x":1246,"y":204.00003051757812,"wires":[]},{"id":"63c11a8c.9927a4","type":"comment","z":"def155ce.cb8dc8","name":"This takes NMEA Output by SeaTalk and adds checksum","info":"","x":506.9999542236328,"y":180.9999542236328,"wires":[]},{"id":"f6520ef8.395e2","type":"serial in","z":"def155ce.cb8dc8","name":"SeaTalk NMEA Input","serial":"c5d7ff46.19d73","x":104,"y":470,"wires":[["4fc0cc12.46de24"]]},{"id":"c2d153f6.75ee2","type":"inject","z":"def155ce.cb8dc8","name":"Inject SeaTalk DBT String","topic":"","payload":"$IIDBT,0008.4,f,,,,","payloadType":"str","repeat":"1","crontab":"","once":false,"x":178,"y":269,"wires":[["4fc0cc12.46de24"]]},{"id":"427edb50.17af24","type":"inject","z":"def155ce.cb8dc8","name":"Inject SeaTalk HDM String","topic":"","payload":"$IIHDM,268.,M","payloadType":"str","repeat":"1","crontab":"","once":false,"x":176,"y":344,"wires":[["4fc0cc12.46de24"]]},{"id":"bc1148e9.02e848","type":"debug","z":"def155ce.cb8dc8","name":"","active":true,"console":"false","complete":"false","x":1254,"y":423,"wires":[]},{"id":"d06bc454.854278","type":"function","z":"def155ce.cb8dc8","name":"Create full DBT string","func":"var nmeaFull=msg.payload;\n\nvar nmeaSplit=nmeaFull.split(\",\");\n   \nvar nmeaFinal=nmeaSplit[0]+\",\"+nmeaSplit[1]+\",f,\";\nnmeaFinal=nmeaFinal+(nmeaSplit[1]/3.28084).toFixed(2)+\",M,\";\nnmeaFinal=nmeaFinal+(nmeaSplit[1]/20).toFixed(2)+\",F\";\n\nmsg.payload = nmeaFinal;\nreturn msg;","outputs":1,"noerr":0,"x":671,"y":253,"wires":[["142750e6.16540f"]]},{"id":"c5d7ff46.19d73","type":"serial-port","z":"","serialport":"/dev/ttyOP_485","serialbaud":"4800","databits":"8","parity":"none","stopbits":"1","newline":"\\n","bin":"false","out":"char","addchar":false}]