SPEEDING UP RS232

[moldmaker]

I would like to speed up my rs232 connection
that goes from my computer to my CNC milling machine. Im at 38.8 right now. I would like to double that speed. From my computer to my machine
is about 200 feet.
I was thinking about using beefer cables. Im shure it will help but I dont know how much.<p>thanks

[Mike]

I think something like this is what you need:<p>http://www.ramelectronics.net/html/EXT-RS232.htm

[moldmaker]

Mike,<p>I think that is for long distances and not for speed

[Mike]

I believe it allows long distance without speed loss like you are experiencing

[philba]

It doesn't spec a speed. I'd be wary when details like that are left out.<p>You could get rs232 to rs485 converters for each end. rs485 is a lot more resilient to noise than rs232 and is spec'd for a lot longer runs. You can probaly use the same wiring. Especially if you can live with half duplex operation. I've not bought from these people but they have a pretty wide selection and fairly decent prices. http://www.rs485.com/pconverters.html You could build your own, for a lot less, though.<p>Another approach is to use ethernet and a serial to ethernet converter. A driver on the PC creates a virtual com port and the serial/ethernet converter presents a serial interface. You can buy them for $300 and up (sometimes cheap on ebay). They are often called serial hubs. lantronix, comtrol, equinox and others make them. Or, you can build one with the lantronix xport or other similar devices. XPORT
These are pretty easy to use and the xport is spec'd up to something like 900Kbps but i suspect you'd see somewhat less than that... The xport costs $50 and you'll need an rs232 driver and a beefy power supply. lantronix only support windows, no linux driver.<p>Phil

[dyarker]

Mike is right, the RS232 spec suggests the max distance for 9600bps is 75ft.; and as speed increases the distances decrease due to cable capacitance and noise pickup. At 38.8 (I think you mean 38.8Kbps) over 200ft. of cable you are lucky it works. To get reliable data flow at higher speeds and/or longer distances you need converter/driver units like Mike suggested, or change to a different standard like Phil suggested.<p>To double the speed and stay with RS232 you need three things; a prayer, more good luck and 22AWG low capacitance shielded cable. Use 2 wires for signal ground. The cable shield gets connected to chassis ground at one end only, either the PC case or the mill.<p>Good luck,<p>[ June 30, 2005: Message edited by: Dale Y ]</p>

[philba]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Dale Y:
...
To double the speed and stay with RS232 you need three things; a prayer, more good luck and 22AWG low capacitance shielded cable. Use 2 wires for signal ground. The cable shield gets connected to chassis ground at one end only, either the PC case or the mill.<p>Good luck,
<hr></blockquote><p>If you want to try the shielded cable, I suggest you get 8 conductor twisted pair shielded. If it doesn't work (and I suspect prayer will be as effective as the cable), then at least you could use ethernet or rs485. Worth a try (the shielded cable) but you don't have great odds on your favor. You can improve your odds by routing the wire away from power cables, electric motors, flourescent lamps, phone lines and so on. 200 ft is pushing it pretty hard. <p>By the way, rs485 is a very common solution for the problem you describe.

[Gorgon]

Hi,
To use a shielded cable / twisted pair on RS232 normally makes things worse. The problem with speed and distance for RS232 is the inbuilt short circuit protection in the drivers. Together with the capacitance in the cable the flanks on the signal is gradually changing to sawtooth shape. When the speed increases you loose the bit pattern. Its a low-pass filtering. It's possible to boost the signal some, but I don't think its possible to increase the speed much from 38.4kBd on 200ft. I once installed a 19.2kBd sync connection on 350ft of cable, but this was just on the border of the RS232 capability.<p>The best solution is to convert from RS232 to RS422 and reconvert from RS422 to RS232 in the other end. Depending on how many signals you are using there are several ready made boxes on the market.<p>Or, you could make it yourself if you are so inclined. I think we could support you with schematics and advices.<p>TOK

[Newz2000]

Just a question...<p>What about something like these serial over RF/BlueTooth modules? I was reading about some over at spark fun... here's a link to notes about range. Here's a list of some of their products and an article that *seems* like what you need.<p>I get the feeling that the serial transfer they talk about is not RS232 but something like uControllers use, but would this be of any use?<p>Baring that, how fast do these devices go that let your satelite receiver connect to a phone line using the power outlets? Can't those be used for serial connections?<p>You know, 5 years ago, serial terminals (used for green screen terminals) were extremely common and there were a ton of devices out there that let you locate these things in warehouses, guard shacks and other remote locations. There really has to be something that will let you get a connection out 200 feet. I've even seen devices that send serial connections over a TCP/IP connection for connecting terminals up in remote offices using a T1.<p>[ July 01, 2005: Message edited by: Matt Nuzum ]</p>

[philba]

The spark fun stuff is RF. I wouldn't use RF for this unless wiring wasn't an option. Clearly that's not the case here. Also, distance vs speed is even more severe an equation than with rs232.<p>Gorgon, why 422 and not 485? I think either would work. Is there a reason for one over the other? <p>Building a 422/485 interface is pretty easy, there are lots of companies that make chips and plenty of designs on the internet. By the way, I tried to sample several maxim transceivers for this a few weeks ago and they didn't have any. The chips are suprisingly expensive ($5 or so), as chips go.<p>Phil

[dyarker]

When I suggested shielded cable I mean NON-twisted pair. Twisted pair is BAD for RS232 because of the shared signal ground.<p>The units Mike suggested probably use RS422 like Gordon mentioned.<p>At 200ft, staying with RS232 on cable is shaky

[Gorgon]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:

Gorgon, why 422 and not 485? I think either would work. Is there a reason for one over the other? <p><hr></blockquote><p>The main reason is that the RS422 is point-to-point and RS485 is half duplex multidrop. Electrical, its about the same. Both are balanced and use twisted pairs. RS422 has separate drivers and receivers and RS485 transceivers. You can of course use RS485 circuits and simulate RS422, but I think its more expencive.(I have not checked!)<p>On top of this you also have the RS423, a unbalanced version of RS422. (Like a 5v RS232)<p>In this case I would use a RS232-to-logic(like MAX232) and a RS422 driver/receiver in each end.(maybe 2 of each for the RS422 if you need RTS/CTS control) You also need a 5volt supply.<p>TOK

[ezpcb]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by philba:

Building a 422/485 interface is pretty easy, there are lots of companies that make chips and plenty of designs on the internet. By the way, I tried to sample several maxim transceivers for this a few weeks ago and they didn't have any. The chips are suprisingly expensive ($5 or so), as chips go.
Phil<hr></blockquote>
It's interesting, Maxim offers free samples here when ever you need, but when you place mass order the trouble comes, lead time is terribly long.<p>422 interface is extreamly easy to built, and the network cable could be used. Once we use networking cable to transfer SPDIF signal to 1km peer, it works perfectly in the lab, but when we install the cables in the building the signals goes wrong. So I think for hi-speed long distance signal transmitting, try to avoid the interference is also very important.

[thesprocket]

For noisy environments, you can completly skip the copper, forget the RF, and move right on to optical fiber.<p>http://www.moxa.com/product/TCF-142.htm#