Late to the party, but what happened to this project? Any luck driving the Trio Servo correctly? I consider doing the same thing using a semi-professional/commercial (arduino-) auto pilot.
Oh, and BTW, your GPS module seems to be upside down. Not good for the sensitivity 
Anyway I have level converter for arduino. Point is recognize protocol for it. Transmission dump would be key.
This depends on what chips they use to implement the RS232.
Most RS232 systems work with the transmitter swinging 0V to +5V which is casually called “TTL level”. Actually classic TTL level is something like +0.2V to +3.5V or some such; since the 1980s everybody has been using 74HC logic which swings 0 to +5.
The above works because the receiver usually has a threshold of +1.5V or so. That is what the standard chips e.g. 14C89 use. Or +2.5V if feeding into a 74HC kind of chip, or into a microcontroller UART (bear in mind the UART input will be upside down so to receive RS232 with it you need an inverter).
There are very few RS232 systems where the receiver has a threshold around 0V and then the transmitter needs to swing -3V to +3V as a minimum. The MAX3232 chips do that, from a +5V supply. A more common transmitter swing is -5 to +5 and the old classic chips (14C88 etc) swing -10V to +10V (with a -12V and +12V supply), and the the classic MAX232A swings -8V to +8V.
So if your transmitter swings 0V to +5V that should work unless they have done a right hack.
Thanks for the serial protocol.
Just to add more info about Trio PWM, as per the info I have available:
Repetition rate of PWM pulses is 100Hz
The pulse width 1.5ms centeres the servo.
Pulse widths from 1.2 to 1.8ms move the servo +/- 45 Degrees.
Trio states that the PWM input expects RS232 voltage levels, but it shall also accept TTL. I am not sure if they really mean less than -3 V for pulse and more than +3V for zero, that is yet to be found out. With also accepting TTL it could mean something like zero being above +3V, pulse is 0V.
Simple rs-232 sniffer is enough
https://www.lammertbies.nl/picture/en_db9_monitor.png
I was connecting parallel sniffing laptop.
It’s 38400 kbps 8N1
RS-232 level single ended or TTL compatible;
I would set up a data capture program on a laptop e.g. I think Teraterm can do this, and capture some packets.
RS232 can have multiple loads so tapping into the data line (I assume it is unidirectional) will work.
Ahh, not this photo :)
I know but I have no feedback what is wrong. It’s just not working. I was playing 2 days to make PWM. It’s 100hz.
Maybe someone was building something like that or have possibility to make data dump from RS-232 communication of original autopilot. It makes work much easier, now It’s blind looking.
Hmmm… you just need to play with it. Looks like it is all there, sort of…
Hi. I know generally RS_232 and programming. Problem is that description of trio protocol is poor, no examples etc. It’s hard to make experiments because one mistake for example in checksum makes that servo is not working.
I’m building it on Arduino mega and razor ahrs + gps receiver.
Now I can controll servo by PWM but it’s not accurate and I cant reach full range. By serial would be perfect.
