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Anyone have any recommendations on a good rs232-to-usb converter. There are a lot out there and from the looks of it some are hit or miss.

Good driver support is a must.

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I hope you mean USB-to-serial (in which case the anwers below apply)? rs232-to-usb would imply that your PC has an RS232 connection and you want to convert it to a USB connection. AFAIK such a gadget does not exist. –  Wouter van Ooijen Jan 12 '12 at 12:24
    
if you have access to a ATMEGA8 and usbasp programmer , you could build one yourself. there is a VUSB project which is a USB to rs232 converter. But it wouldn't convert the logic level to RS232, instead you need MAX232 like charge pump circuit for that. –  Standard Sandun Feb 21 at 3:21
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5 Answers

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Any FT232 chip is good(ie FT232R). The drivers are publicly available and windows will download automatically.

It will show up as a serial port and there are many pre-built solutions available. The Company that makes the FT232 chips, FTDI, will sell many solutions they developed in-house, also.

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One note: The FIFOs on these chips tend to be pretty deep (as in 512 or 1024 characters deep!). That's good for most uses (obviously it keeps the data moving better), but if you want to receive single bytes with low latency, it can be a problem. I don't know how to adjust this for Windows, but if you need help with Linux, search the linux-serial mailing list for my name (Kohne) and you should find my relevant hacks. –  Michael Kohne Dec 3 '09 at 2:55
    
Yes, the other issue here is people forget often that USB is not like serial, it is not a dedicated connection with instant bus arbitration. If you are using USB, you must accept that there is a latency involved with it. We end up with a 20-100mS latency normally, a real serial port would be preferable, but what customer will have one. –  Kortuk Dec 3 '09 at 3:00
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+1 -- I was going to say the same things. I've used FTDI chips successfully with 921.6 Kbaud and yet have rarely run into any buffer overruns on my PC, so they've done a good job with both the hardware and Windows drivers. –  Jason S Dec 3 '09 at 5:14
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@Michael K: FIFOs won't affect your latency unless they're badly designed. The latency with any USB <-> RS232 converter is primarily due to the inherent USB timeslot restrictions, as Kortuk points out. –  Jason S Dec 3 '09 at 5:16
    
Yes, we have also implemented very very high baud-rates, it has been excellent so far. –  Kortuk Dec 4 '09 at 1:04
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USB-to-serial adapters live and die by their driver support. In my experience, FTDI has great support on all three OSes (Mac OS X, Windows, Linux), but the chips are a bit more expensive. I remember Prolific having great support on Linux, but the Mac drivers kinda sucked.

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I use them for the drivers, which is why I make my choice, if a single client has a problem, it makes all of the cost saved go out the window. –  Kortuk Dec 3 '09 at 1:42
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I have used the Prolific chipset in this product and it is extremely reliable. Like the FT232, it shows up as a serial port. I have used it in many of my projects without problems, the best example would be this one where it survived me pulling the rs232 end apart to connect directly to some of the pins.

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Are you looking for a chip, or an actual device? Keyspan used to make great devices - usually a USB to DB-9 adapter. I haven't had cause to buy a new one lately.

On the chip front I've been nothing but happy with the various FTDI based solutions I've tried (though they were all going to TTL-serial, instead of RS-232).

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Keyspan's OK, we have those at work and they're one of the few non-FTDI devices that has worked well for me. it didn't go up to the baud rate I had hoped though. –  Jason S Dec 3 '09 at 13:50
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CP210x from Silabs is a great product. It's difficult to solder, but have lots of tutorials teaching this on Google.

The advantages is that don't need crystal and uses only some capacitors.

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