Need serial port advice (RDS)

[bhays]

Okay, I have an EDM-LCD-RDS transmitter, rds works fine via direct serial port connection with the supplied cable which has a DB9 on one end and mini-usb on the other.




However, I need to locate it physically quite a distance from the PC and wanted to use a serial over IP device to do so. I purchased a Startech RS-232/422/485 Serial over IP Adapter to use for that purpose.

I have the serial over IP adapter set up and working fine as well with the virtual serial port on the pc. After losing several hours fighting this, I have learned that the MiniRDS communicates using synchronous data rather than asynchronous as most serial devices. But, my Startech unit supports RS485/422.. which are synchronous, correct? So I should be able to make this work.
Here's the setup page from the Startech device and the pinout info from the manual.



So I guess I need to go to Ratshack and get a DB9 connector, but how do I wire out? Can anyone help?

[bhays]

On the forum at pira.cz someone told me that the problem is that the miniRDS communicates synchronously vs asynchronously and that no serial over IP adapter could deliver synchronous signals... but that doesn't make sense given that the converter is equipped for RS485/422 and they were not familiar with the Startech unit.

I am wondering if I just need to match the pinout from the RS485 terminal on the converter to the pins on the cable with the transmitter that has a 9 pin serial connector on one end and a mini-usb on the transmitter end...is it converting from asynchronous at the pc com port to synchronous on the transmitter end?

[tpctech]

On the forum at pira.cz someone told me that the problem is that the miniRDS communicates synchronously vs asynchronously and that no serial over IP adapter could deliver synchronous signals... but that doesn't make sense given that the converter is equipped for RS485/422 and they were not familiar with the Startech unit.

I am wondering if I just need to match the pinout from the RS485 terminal on the converter to the pins on the cable with the transmitter that has a 9 pin serial connector on one end and a mini-usb on the transmitter end...is it converting from asynchronous at the pc com port to synchronous on the transmitter end?

Brett,

Interfacing my MiniRDS to LOR is on my list to do this year! If the RDS is synchronous only. The best way to extend the wire so to speak would be a RS-232 to RS-485 and RS-485 to RS-232 convertor. This converters just change the transport from unbalanced to balanced and really don't care about syn or asnyc data. They don't convert the data at all.

B&B electronics has a good selection of convertors.

Depending on your cable run I had very good success running a long probably 200ft of CAT5 to my LED sign from the computer this past year. I use custom wired RJ45 to DB9 adapters. The way I wire these is the transmit pin 3 wire is twisted with a ground and the recieve pin 2 is twisted with a ground. I then use the other 2 cat5 pairs for the pin 5 ground and other pins if needed.


KEN

Lights on Bell Road

PS we met at the Indy Mini last year. Email me if you need more specific help. ken@tpctechnologies.com

Have you worked on the exact serial strings the MiniRDS needs? I used a static message is past year and have not looked at it yet!

[bhays]

Brett,
The best way to extend the wire so to speak would be a RS-232 to RS-485 and RS-485 to RS-232 convertor.

My situation is that my show computer is located in my office next to my other pc on a kvm switch.. two video cables on a splitter run from it for two projectors during the show.. so really would hate to move it.. the transmitter is in the garage next to the network switch and wiring panel for the house..I have network there, but no spare cat5 cable to run serial over.. (I could split the cable and use two pairs for network and two for serial and will do so if I must) Ken, that's when I will be asking for help because this stuff is all new to me in terms of synch/asynch...

So, I really need to figure out a way to use the network connection.

I am going to try a different approach. I have a usb-serial adapter that works fine with the RDS and from what I have read, usb-serial adapters work well with usb over ip.. so I am going to use usb over ip to get to the garage, then plug the usb-serial adapter into that.. should work from experience of others.

I've had to drag a serial cable across the room the last three years for X10 due to issues with the subpanel my office is powered from (bridge in the panel didn't do the trick).. so I am going to use the serial over ip adapter to move the CM11A out to a circuit off the main panel in the garage...

Plus, I use VGA Baluns to run video to the projectors.. so it's quite the complicated wiring mess...;)

[richms]

They are probably bitbanging on the serial handshake lines to send data out, not using the data lines - had a cheap personal organiser that did that and it wouldnt even work on a USB-Serial adaper as it was trying to toggle the handshake lines too fast. If it is slow enough then the USB-Serial will work, but the CPU use will be really high.

No idea for sure if it is bitbanging, but their blatent non standard use of a connector shows they dont care for standards in anycase. Find the pinout for the cable and that will show for sure, pins 2 and 3 are the real data pins. Chances are they go nowhere.

[bhays]

They are probably bitbanging on the serial handshake lines to send data out, not using the data lines

Bingo. I learned this on another forum:

But I will caution that it is more complicated than just sync vs async. As I understand it, the RDS data is not on the serial data pins at all. But rather, they are using the handshaking pins (CTS/RTS, or similar) to pretend to be an I2C communication buss. This implies that they have to be able to assert, or clear, or report the state of these pins fairly accurately through the remote solution. And they are exactly the pins that are generally considered lowest priority to pass along in a timely fashion...

The good news is that the usb over serial solution works just fine. I am using a DIGI USB/Anywhere device to get from the pc to the garage over the LAN and then I have a usb serial adapter plugged into it, then into the transmitter. It works fine this way by transmitting the usb signal over the network rather than the serial.

[Entropy]

You could perform the conversion using an Arduino or similar device, which has RS-232 serial along with I2C.

You just reminded me that I need to add my current "test master" firmware for my I2C RGB LED project to its github repository - that "test master" would be a good starting point for the Serial->I2C converter you would need to communicate with a MiniRDS.

[richms]

IMO its absolutly nuts that they have put that mini USB plug on the device, and to try and bitbang in this era of the OS preventing the accurate timing needed for that sort of thing to be reliable.

[Entropy]

I2C as a master doesn't really need accurate timing, since the master generates the clock and it's rarely ever a problem if the clock is slow or has insane jitter.

[richms]

If there are timeouts in the device then there could be problems. Any idea what chip is on the encoder?