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flysideways
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PostPosted: Sun Apr 14, 2013 2:31 am    Post subject: RS-232 to USB Reply with quote

Which is your favorite. I would like one that works equally well in Gentoo, OSX and Windows. I still have RS-232 equipped desktops but would like to use my laptop with a couple of devices.

I tried one from Fry's, the only one they had, and it did not work. It was recognized as a Prolific chip but the Windows drivers, XP and 7, failed to start with an error that Prolific says is common to counterfeit chips.

Fry's, go figure, 580 Market, sure.
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pjp
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PostPosted: Sun Apr 14, 2013 3:38 am    Post subject: Reply with quote

I've used one from cables to go, but only under XP. When it worked/works, it seems fine. Its driver or Windows doesn't like it being unplugged too often, or Windows appears to lock up (I usually give up waiting and power off). I've also experienced random character gibberish, so trying to login or type commands becomes impossible. I haven't pinned down if that is a hardware of software problem (it isn't a configuration issue). Personally, just give me the rs-232 port.
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tylerwylie
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PostPosted: Sun Apr 14, 2013 5:27 am    Post subject: Reply with quote

I've used a bunch of random ones with success in all versions of Linux. Most are very well supported and show up as something like /dev/ttyUSB0 or what not. In Windows they suck complete ass. Your request for one that works in all 3 presents me with great lols. I wish you the best of luck sir.
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Naib
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PostPosted: Sun Apr 14, 2013 7:24 am    Post subject: Reply with quote

They are OK, most use an ftdi usb->parallel data chip or a prolific chip. Both can then be set into but bang mode from the drivers.


Be warned! Rs232 spec actually calls for -15 to +15v signals. These converters will at most give you 5v. That might be OK for you but if you have a piece of equip that is only sensitive to 15v it won't actually work.

The only USB to serial comma converter I have that works is one from NI it costs like £80 but is fully spec compliant (the driver ui has a 5v and a 15v option) and does rs485 and rs422 as well
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energyman76b
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PostPosted: Sun Apr 14, 2013 12:23 pm    Post subject: Reply with quote

in short, get a cardbus serial port card.
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pjp
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PostPosted: Sun Apr 14, 2013 12:33 pm    Post subject: Reply with quote

Wow. I didn't realize they still made PCMCIA cards.
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ratmonkey
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PostPosted: Sun Apr 14, 2013 1:55 pm    Post subject: Reply with quote

I still find the need for RS-232 all the time because I work with industrial control systems that have 15+ year life-cycles. The cheapo usb-serial converters just can't hang unless your device is only a few inches away. Like someone already mentioned, most of them only use +/-5V. I think the minimum spec on RS-232 is +/-3V for a high signal so it doesn't take much voltage drop due to cable length before you start flipping bits during transmission and get garbage on the other end. Typically if they come with a separate power supply, that's a good sign because as much as it's a clunky hassle, you're pretty much guaranteed that it will provide the appropriate voltage level.

I've had luck with Moxa's U-port line:

http://us-mkt.moxa.com/mus-english-ha-usb-to-serial/?_kk=usb%20to%20rs232&_kt=20d4aede-a39b-4dc2-876c-2b1bd7bf5333&gclid=CMqI1-WjyrYCFYHc4AodeCYA7Q

The other option is to just use an Ethernet enabled serial server. If it's a device I connect to often, this is the route I usually go. Then you can use simple apps like telnet or netcat to interact with the device with your network connection.
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pjp
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PostPosted: Sun Apr 14, 2013 4:23 pm    Post subject: Reply with quote

I've seen Moxa used in critical applications. That'd be the rack solution I'd go with if I needed one (or could implement one). Unfortunately, laptop / back of rack is where I've needed to use the usb "solution."
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flysideways
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PostPosted: Sun Apr 14, 2013 9:24 pm    Post subject: Reply with quote

Thanks for the input. I've just used the computer that still had the port. I also remembered that I still have an old Epia board that could do this duty.

Still looking at the portable solution but no hurry.
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Naib
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PostPosted: Sun Apr 14, 2013 9:38 pm    Post subject: Reply with quote

make your own :)
FTDI FT232 and a RS232 tranceiver chip plus some R,C,D and a connector
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eccerr0r
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PostPosted: Tue Apr 16, 2013 5:50 pm    Post subject: Reply with quote

I have three Belkin-branded USB-to-RS232 (two are built into an all-in-one usb hub). They seem to work perfectly fine for regular asynchronous RX/TX data with the generic USB-RS232 driver. I don't think they will work well if you want to bit bang the control lines or read the status lines to receive data at high speed...

I have not measured the high/low voltages on them though...
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