In article ,
"Dave Plowman (News)" writes:
In article ,
Andrew Gabriel wrote:
In article ,
"Dave Plowman (News)" writes:
I need a longish serial cable to get from the workshop computer to the
bench. Say 4 mtr. I already have the D connectors and wonder what
would be the most suitable cable I have 'in stock' Only need the send
and return - no 5v. Would balanced mic cable do - or two co-ax? I do
have some decent video co-ax but two would be a bit big to fit the D
connector shells.

4m is not long for an RS232 style serial cable run, and almost
anything will do, although it gets more critical at higher bit rates.

The device I need to connect to says 115200 baud.

OK, that's quite high, but shouldn't be a problem. I've run 921600 baud
at 2m with correct cable without any data corruption, and it may have
gone further (didn't test). All modern UARTs do 8 or 16 times over-sampling
anyway, which means they cope with much worse signals than the original
RS232 specs allowed for. If you are running an error detecting/correcting
protocol over the link, you can get away with some corruption. If not,
then you need to consider the effect of any corruption.

You'll need a 3-core (or more) screened cable, and I would avoid twisted.

I used to buy quite a lot of made-up serial leads from CPC and they were
cheaper than you could buy the connectors alone, but their range seems to
have dropped to just two products now, and not long enough for you.

Conventionally, untwisted screened cable is used, although there
are variants which use balanced drivers for the signals, which
require a twisted pair per signal.

This is definitely unbalanced.

Not sure what you mean by "return". Do you mean send and receive, or
just unidirectional send and the ground return wire?

No - TX and RX and obviously ground. Those are the only connections on the
device DB9.

OK. Although DB9 combines signal ground and screen ground, I would
not use the screen as the signal ground in the cable, hence 3-core
plus screen, and connect the screen at just one end.

Presumably the device uses xon/xoff flow control, or guarantees to
be able to receive at full rate and doesn't send large blocks of data.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]