Posted: Wed Jan 08, 2014 3:56 pm Post subject: finally nmea data from tacktick !
Now i have tested the "solution" to get nmea data out of a tacktic T122.
As reported earlier T122 does not conform to nmea183 ( or rs422 ), it's simply broken.
To solve this i bought a rs232tors485 board from eonkits ( http://www.electrokit.com/rs232-rs485-interface-r.46114 )
The board needs only be half-populated, the MAX232 and d-sub is not needed.
Signal to the max485 is taken from the so called nmea-out+ on the T122 ( it's driving between zero and +4V which is enough).
The kit has an on-board 7805 regulator so it can be supplied from the boats +12V, all needed extra stuff is a cooler for the 7805 ( it will get +60 degrees C if no cooler is mounted). I plan to use the cooler as part of the mounting hardware and mount it on the back if T122.
I have my Tacktik unit now even by Raymarine, waiting for what it does when it comes back from repair.
In the meantime I've been busy myself thanks to the circuit diagram of Frank to understand the input circuit.
For weak signal sources is the pose significant burden
Therefore, I developed a different version.
The opto-coupler is driven here by a constant current source.
This allows a greater dynamic without placing undue burdens on the source A few pictures from the simulation by LTspice:
Input voltage source ± 10 V, and R with 650 ohms in series.
In comparison, the current through the transmitter diode.
I will modify an input of multiplexer accordingly and report whether this change had success.
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