[Xastir] I finally got it!

[Curt, WE7U]

On Fri, 17 Sep 2010, Curt, WE7U wrote:

> Do you have a meter?  Analog or DMM?  If so, you can check between
> pins 5 (GND) and 2 on a DE-9 (contrary to public opinion, it's a DE
> and not a DB for a 9-pin).  Then do the same for pins 5 and 3.  2
> and 3 are your TXD/RXD pins, which are the ones your data goes down
> in each direction.  If pin2 on one connector is being driven (+3 to
> +12VDC or -3 to -12VDC) then you don't want to connect it to another
> connector that also has pin 2 driven.  In that case you'll need a
> null-modem cable or adapter to connect the two.
>
> If pin 2 is driven on one, and pin 3 is driven on the other, then
> you can connect the two.

I should have mentioned that you can do the same with a resistor and
an LED.  Size the resistor for 10mA or so at 12V, so maybe a 1k or
1.2k resistor at 1/8W or larger.  Nearly any LED will do.

Solder the resitor to one leg of the LED and then use the other lead
of the resistor and other lead of the LED as your "meter" to see if
a pin is being driven.  If it's not being driven it's either a
receive pin or it's not connected in your cable.

Combine that setup with a 6V to 12V power source (batteries?) and
you can test cables to see how they're wired.

-- 
Curt, WE7U.                         <http://www.eskimo.com/~archer>
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