Connect to ST1000+ Autopilot

[j-lang]

Has anybody tried to extend the software for connecting a Raymarine ST1000+ Autopilot.
From ST1000 users guide:
Recognized NMEA data
The following table lists the recognized NMEA sentences.
Information NMEA 0183 data
Cross Track Error APB, APA,RMB, XTE, XTR
Bearing to Waypoint APB, BPI, BWR, BWC, BER, BEC, RMB
Distance to Waypoint WDR, WDC, BPI, BWR, BWC, BER, BEC, RMB
Waypoint Number APA, APB,BPI, BWR, WDR, BWC, WDC, RMB, BOD, WCV, BER, BEC
Speed Through Water VHW
Apparent Wind Angle and Speed VWR

Some of these Sentences are generated.
For implementation an additional serial port and external rs 422 converter for 3,3v interoperability would be necessary for driving the tiller pilot.
Am I right?
Does somebody made this or a similar extension or is it supported out of the box?

[Rodemfr]

Hi j-lang,

I have a setup in my boat which is has some similarities to yours : MTN GNSS input is connected to my AIS RS422 to get both GNSS position (GLL/GGA/RMC) and the AIS data (VDM/VDO) which is forwarded to my tablet. To solve the RS422 problem, I'm not using a transciever. I added two resistors to divide the 5V AIS- signal to 3.3V. Since my AIS and MTN share the same ground line, it is OK to connect this directly to the RS232 pin of MTN, without connecting AIS+. I don't remember the values I used for my resistors, but it is a pretty high value, >5k, to reduce power draw to almost zéro. It is OK since the bitrate is low (38400 baud).
In your case, you want to transmit. When I read the datasheet of a RS422 transciever and it will interpret a "one" as soon as the voltage difference is more than ~200mV, so you can probably connect directly the RS232 output of MTN to NMEA- and the ground to NMEA+ (NMEA0183 is inverted in RS422). The 3.3V of the RS232 should be more than enough for the receiver.

I'm also preparing a new version of MTN associated to a dedicated PCB designed with EasyEDA Pro, the free EDA provided by JLBPCB to order fully assembled PCB. You can see it in the hardware_v2 branch. It has been inspired by your hardware_v1 work. This version has a RS422 receiver (not transciever, I'm receiving only). I ordered 3 units that I should receive in 2-3 weeks. I can send one to you if you want (and if it works...).

[j-lang]

Thank you for your update. My parts are currently in a winter store and will check interface voltage.