USB-to-Serial Interface Alternatives

[Josh Adelson]

Yesterday at the WPI scrimmage I learned that program downloads to the robot are much faster going out directly through the computer's serial interface rather than through the USB-to-Serial convertor. I tried setting this up however the DB9 serial interface supplied by Radio Shack does not fit the DB9 serial interface on my computer, because it has two female screw threads in the way (they hit up against the two female screw threads on the male serial interface on my computer).

It seems to me that the only solutions to this are 1) a DB9F to DB9M cable, in which the DB9M end has no protrusions of any sort or 2) a DB9F to RJ11F cable. The latter would be ideal as it would allow any standard phone cable to hook into the micro controller on the robot. Unfortunately, I cannot find either of these cables.

Questions:
1) For people who are using a direct serial interface from the computer, how are they doing it?

2) How much faster is the download time? (In other words, how important a problem is this to solve?)

Thank you,
Josh
FVC Team 78

[Mark McLeod]

My laptop has a DB9 Male serial port and I use a standard DB9 Female/Male serial cable to connect to the Vex programming module.

Look for a standard DB9 cable that has two mounting screws on each end rather than any posts and they won't obstruct connecting, e.g., http://www.cablewholesale.com/specs/10d1-03203.htm
They can be found at CompUSA.

Downloading is 10-20 times faster with a native serial port than it is with a USB-to-serial converter like the one that comes with the Vex programming kit. It's most noticable when you're making lots of changes rapidly and trying to download them all.

[DonRotolo]

Originally Posted by Josh Adelson

I tried setting this up however the DB9 serial interface supplied by Radio Shack does not fit the DB9 serial interface on my computer, because it has two female screw threads in the way (they hit up against the two female screw threads on the male serial interface on my computer).

Josh, look closely at that cable, you will see that the female nuts on the cable can be unscrewed and removed - they are just little nuts that are about 1/4" long, not a permanent part of the cable. Hold nut with pliers, turn screw with fingers....

After removal, you have male screws on each end, just what you need.

Don

[Josh Adelson]

Mark, Don, thank you both for your responses. I actually had tried removing the nuts - on my unit they turn but they don't unscrew. I will try that DB9 M/F cable.

[BradAMiller]

Originally Posted by Josh Adelson

Mark, Don, thank you both for your responses. I actually had tried removing the nuts - on my unit they turn but they don't unscrew. I will try that DB9 M/F cable.

In the demo at WPI this past weekend we were just using very inexpensive DB9 male to DB9 female cables. That solves the clearance problem with using the orange box directly.

[Kingofl337]

You can also goto www.newegg.com and Search for PCMCIA RS-232.

That is alot faster then a USB adapter.

[Roger L. Ruszko]

Josh, FVC Team 78

Questions:
1) For people who are using a direct serial interface from the computer, how are they doing it?

Serial interfaces have been with us much longer than USB. There are cables with either type of connector (male pins, female sockets) on each end. Plus having either the male screw pins or female nuts. Watch the wire configuration in the cables from pin to pin. There are also cables out there that look like serial cables but serve as Null Modem Cables. You just have to spend some time hunting through cables (new or used) until you find one that fits your needs.

You may be able to pull some of the nuts off or screws off of the cable connectors and thus allow the cables to plug into the connectors. You may not get a "permanent" connection of cable to computer or cable to adapter. However the connection can be make and the mission accomplished.



2) How much faster is the download time? (In other words, how important a problem is this to solve?)

You very likely need to solve this problem if you are using an older computer not equipped with a USB port. For some its not a question of time and speed it is a question of need.

Roger L. Ruszkowski

[Josh Adelson]

I got the right cable at the last retailer I tried... Radio Shack! It does download much faster now. Thanks everyone for your help.

[dez250]

Like Adam said, If you are looking for an efficient way to add a serial port to a laptop that doesn't have one i would recommend a pcmcia to rs-232 adapter over a USB adapter.