?? about Rs-232 to Ethernet converters.

Browsing the TWI site I see that at least one of their rs-232 interfaced stations needs a null modem cable to connect to the PC, so I think we need to confirm that we are connecting it the correct way.

DB9 Pin 5 is ground, and 2 and 3 are the data lines. Measure the voltage between 5 and 2, and 5 and 3. One should show very little voltage, that’s the data input, and the other should show +/- 5 volts or more, that’s the data output. If the station is continually sending data you may need to have the meter on AC volts, if it’s just waiting for instructions it will be a DC voltage. (If you have a 'scope then I’m sure don’t need to tell you want to do :wink: )

On the converter Pin 3 is the data input, Pin 2 is the data output. If the TWI is the same then you need the null modem crossover.

No scope, I know just enough about this stuff to be dangerous. :wink:

Not sure what you mean by sucking power from the serial port? If running the station from that, no it has a wall wort transformer.

Pin 3 on the TWI db9 measures 9.53v DC. Pin 2 @ mv.

Data output pin on the ethernet conversion card measures 5.3vdc.

Station came with a null modem serial cable, which is what I always used to the computer serial port. I’ve tried using same cable with the Ethernet converter, no luck.

In the picture’s, you will see the beige radio shack item which is a null modem adapter.

See pictures here:
https://drive.google.com/file/d/1K9uiyJnSW80-WcRGJol7VWB052E5KIZ7PA/view?usp=sharing
https://drive.google.com/file/d/1qWZ2d7qegEZqVjDdl6ORLeVMFc1zrN0aJQ/view?usp=sharing
https://drive.google.com/file/d/151Kii6-3qxnp9XeHQh-unmQL09jMx3-gzw/view?usp=sharing
https://drive.google.com/file/d/1ydW_Cr4GsY71FiEvhZSgiE0dctylv4MZDQ/view?usp=sharing
https://drive.google.com/file/d/176gjHUs6il3LCcpr_uBwndjqcp6Tw_DydQ/view?usp=sharing

“Pin 3 on the TWI db9 measures 9.53v DC. Pin 2 @ mv.”

“On the converter Pin 3 is the data input, Pin 2 is the data output.”

So TWI 3 needs to go to converter 3, and TWI 2 needs to got to converter 2, IOW, in this instance you need to be using a straight through cable, not a null modem.

OK, not an issue then. You can run very low power devices from one of the serial port control lines, but it’s a pretty flaky thing to do IMHO :roll:

I admit defeat. :?

I’ve tried without a null modem, and still no joy.

Any chance I damaged something by using the null modem when it shouldn’t have been used?

Plug it back into the computer serial port, and no issue.

Thanks for your help, it’s appreciated.

Dazed and confused.

Bummer :? It’s plug and play for the Davis, and I’ve used them with other serial devices too. I’m sorry it didn’t work out for you :dontknow:

I may call Twi tomorrow, and see if I can get any further info about their RS232 port. It is designed so it could use either a Serial Printer or a standalone dialup modem for report use sage as well as computer interface. There are some settings in the station that can change how that works. But they are poorly explained in the manual what exactly the settings do the to RS232 output.

And technically, all I should need is those 3 lines connected, correct?

I can say that almost all serial devices will communicate with only those lines connected, but now I’m wary of assuming anything about the TWI. Do remember that the testing showed you do not need the 2 x 3 crossover.

Reason I asked, grasping at straws here, that maybe the other control lines from the TWI is somehow confusing the serial port on the converter.

Odd finding, I can do the loop back test by using two instances of Hyperterm, like I did before. 1- hooked to serial, one hooked to ethernet. But for the first time, I attempted to connect it via RS232 for the setup program. Changed the CFG jumper as required, but the setup program fails to connect to the converter via serial, it’s times out.

Wasn’t able to call TWI today.

Thanks for tolerating my obsessive behavior with this. :oops:

I think the 3 wire connection is worth a try.

No problem, I would be exactly the same. Maybe you could measure the voltage on all the TWI DB9 pins (using 5 as ground) and that might yield a clue?

Only three wires is a no go.

TWI DB9 Pin Volt measurements with meter black lead remaining on Pin 5. With nothing but the meter attached.
1: 7mv
2: 5.9mv
3: 9.53vdc
4: 9.17vdc
5: grnd
6: 2.2mv
7: Negative 60mv to 299mv, always changing.
8: Negatvie 24mv to 100mv, always changing.
9: 2mv

Ok after further head banging on the wall moments and a lot of digging, I find that the USR RS232-24 only use’s the tx rx and grnd pins. Nothing else is active on it. Using an ohm meter on the USR to trace pins to the circuit board pretty much confirms this.

I ran across the following article that leads me to believe some subset of what he say’s may be used in my case by jumpering pins on the weather stations RS232 port.

Article:
A Null Modem is used to connect two DTE’s together. This is commonly used as a cheap way to network games or to transfer files between computers using Zmodem Protocol, Xmodem Protocol etc. This can also be used with many Microprocessor Development Systems.

Null Modem Connections
Figure 1 : Null Modem Wiring Diagram

Above is my preferred method of wiring a Null Modem. It only requires 3 wires (TD, RD & SG) to be wired straight through thus is more cost effective to use with long cable runs. The theory of operation is reasonably easy. The aim is to make to computer think it is talking to a modem rather than another computer. Any data transmitted from the first computer must be received by the second thus TD is connected to RD. The second computer must have the same set-up thus RD is connected to TD. Signal Ground (SG) must also be connected so both grounds are common to each computer.

The Data Terminal Ready is looped back to Data Set Ready and Carrier Detect on both computers. When the Data Terminal Ready is asserted active, then the Data Set Ready and Carrier Detect immediately become active. At this point the computer thinks the Virtual Modem to which it is connected is ready and has detected the carrier of the other modem.

All left to worry about now is the Request to Send and Clear To Send. As both computers communicate together at the same speed, flow control is not needed thus these two lines are also linked together on each computer. When the computer wishes to send data, it asserts the Request to Send high and as it’s hooked together with the Clear to Send, It immediately gets a reply that it is ok to send and does so.

Notice that the ring indicator is not connected to anything of each end. This line is only used to tell the computer that there is a ringing signal on the phone line. As we don’t have a modem connected to the phone line this is left disconnected.


nullmode.gif

If I understand it correctly, with just a 3 wire null modem (2x3 crossover) connection, the station doesn’t communicate with the PC - right?

If so I would try the 3 wire null modem connection to the PC with those links added, and see if that works. If it does then uncross 2x3 and try the same with the adaptor.

3 wire connection null or nor straight does not work, correct.

The TWI does not use pins 1 & 9 on it’s DB9 for anything.

So, In my mind, tying pins 4 & 6 together on the TWI, and 7 & 8 on the TWI could/should make it work, right?

And not fry anything in the process?

1: 7mv
2: 5.9mv
3: 9.53vdc
4: 9.17vdc
5: grnd
6: 2.2mv
7: Negative 60mv to 299mv, always changing.
8: Negatvie 24mv to 100mv, always changing.
9: 2mv

4 looks like an output, and 6 an input so I would try that link first, not sure what’s going on with 7 and 8 but the voltages are so low I doubt it would cause any harm.

“And not fry anything in the process?” - RS232 ports are usually pretty robust and to me it seems like a reasonable thing to do, but it’s your station.

We have lift off!! WOOT!

After finally getting a hold of someone at TWI that understood what I was trying to accomplish, they confirmed that tying pins 4 and 6 together on the weather station would cause no harm. And that was the solution! 8)

Thanks for tolerating all my questions Niko!

Wow good job :occasion5:

Those converters are great, especially now they are less than $20. I was surprised nobody was interested when I posted the “how to” for the Davis :dontknow:

Brian has WD all fixed to work with my station and the TCP converter! WD has been running via the TCP for 4 days now, no problems. Technology is great…mostly. :wink:

I agree, these are a great for eliminating serial cables and solving distance problems.

Wifi version would be great if you don’t already have network cables everywhere.

Thanks for the heads up on these Niko!

I do have a Chinese WiFi/RS232 module, but just reading the instructions is enough like ](*,) that I haven’t taken on the challenge of getting it to work yet :roll: It seems to want to be a wireless AP/router instead of a simple network client :? One day…

Finally got around to mounting this to the back of the station, instead of it just floating free.
Finished project.


project.png