Hi Mark,
That's the spec I am currently using. But, I had one question that
I have not heard back on yet, that of signal ground vs chassis
ground. I have them tied together on the OBDII connector end, but
wonder if we should only connect signal ground, or if they should be
separate wires between both ends, or just leave the chassis ground
unconnected. I've seen it done various ways in various OBDII
hacking diagrams. Is there even a chassis ground pin on the DA26
connector?
Functionally it probably doesn't make a lot of difference, but for
RFI/EMC purposes, it may be important. I always assigned that task
to someone who knew what they were doing :); I just knew it was
something to be attended to. Without over-engineering this, what is
the right treatment for chassis ground?
15cm cable length should be ok, as HUDs should have long enough
cables to reach under the dash, but my first reaction was that it
seemed a bit short. I guess it depends on where and how the OVMSv3
module gets mounted. The cable should be long enough to be able to
to be tied back to the unit and/or its mounting situation.
Otherwise, an OBDII dongle would be forced to just hang there,
potentially over or under one's feet. Maybe 25cm would be better?
Greg
Mark Webb-Johnson wrote:
Regarding the HUD cable, I have asked the suppliers for this,
according to the following specification:
OVMS 3 HUD expansion cable:
Pinout: “HUD"
J1962-F DA26-M
Signal
4 8
Chassis/Power GND
5 8
Chassis/Power GND
6 16
CAN-H (primary CAN)
14 6
CAN-L (primary CAN)
16 18
+12V Vehicle Power
Notes:
- Require
120ohm resistor between DA26 pins 16 and 6 (this can
be either at J1962 or DA26 ends).
- J1962 pins 4 and
5 are both connected to single DA26 pin 8.
- J1962 end
should be FEMALE plug with straight cable. DA26 end
should be MALE.
- Both ends
should be enclosed in shells, and cable should be
15cm in length.
I think that is correct. If there are any changes, please
let me know.
Regards, Mark.
Hi Steve,
Ha, didn't know that. Thought they were all DB's...
Thanks, corrected.
Greg
Stephen Casner wrote:
Greg,
A nit: The connector is more correctly identified as
DA-26, see
https://en.wikipedia.org/wiki/D-subminiature
-- Steve
On Tue, 27 Mar 2018, Greg D. wrote:
Hi folks
In a fit of prose, if not Shakespeare, I took a pass
at creating the
documentation chapter for the OBD2ECU task.
Comments, corrections, and
general feedback is requested. Is there anything
significant missing?
Mark, if this looks acceptable, can it be posted to
the Google Doc, or
send me an invite such that I can do so?
Note that I don't have any reference material on the
OBDII-to-DB26
cable, other than the wiring. If we eventually have
a purchase source,
that should get referenced, or lacking that, perhaps
pointers to where
the connectors can be purchased? Placeholders are
noted, but only
that. For the EEs in the group, a question: I have
both signal and
chassis grounds connected together on the OBDII
connector; should they
be, or just signal ground?
I think it would also be helpful to include a table
of what metrics are
available (supported) on what vehicles, as an aid to
those who want to
remap things for monitoring on an OBDII HUD or
Dongle. A glance at the
available documentation didn't turn up anything, so
I took a first pass
at the table. See the attached, which includes what
I know of the
Roadster's implementation (since I have one and have
studied the code a
bit). I would rather not try to guess at the other
cars. Could the
various vehicle authors contribute their columns to
the table? Send me
an updated spreadsheet, and I will do the merge.
Thanks!
Greg
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