Tuesday, February 16, 2010

RS-232 - 253 = RS-485

If RS-232 isn't enough fun for you, you can always try RS-485 to get around its limitations. The main benefits of RS-485 are longer range, higher speeds, higher noise rejection and support for multiple end-points. The main downside is that it cannot support full duplex communications. This tutorial has some information about why you might want to consider RS-485 for your next project.


Fozzillo said...

In my experience I have been using RS-422 to control multiple pan-tilt security cameras at distances exceeding 1200m. The controller was developed by the company I was working for.

I Heart Robotics said...

I think 1200m is one of those best guess estimates for an environment with reasonable amounts of interference.

Were you also sending video over the RS-422 link?

Did you have issues with termination?

I remember how bad the termination issues were with old SCSI-1 drives.

Fozzillo said...

It was more than 10 years ago, but I remember that, for long distances, the termination wasn't nominal, it was chosen by trial and error procedure.

No video, only control commands at 9600 BAUD, sometimes less. The video signal was transported by standard coaxial cables, but we boosted the signal to 50% more than 1V. Our competitors used a proprietary video signal at 2V, they won when it came to making the system for Italian highways video monitoring.

At the time digital video (over IP) was possible but the standard analog way was considered more reliable, so we developed all kind of systems, to switch and multiplex analog video signals, we had a motion detector that was incredibly expensive and complex 10000$/channel), now any freeware
software is better than it was.

We did manage the installation only for big projects like highways, once I sold and installed one in a oil refinery, no sparks allowed.

I first started as the instruction manuals writer, then I became a seller for the company. We also produced broadcast monitors (with added OSD infos), medical monitors, airport monitors.

We were the last company to produce monitors in Italy, now it's all from Asia.