Serial RS232 directly to a USB DAQ?

[jeanlucpicard]

Hello,

I have a question regarding serial communication: is it possible to directly hook a device via RS232 serial to digital pins of a USB-6211 DAQ? (Or maybe even a USB-6008?)

If so, where should I wire the pins to?

If not, could you recommend me a not too expensive, yet functional RS232 to USB adapter which could work fine? (I am planning to interface a Datex capnometer or a Fresenius Pilot C infusion pump first, however if I could find a relatively well-priced multi-port adapter I would go on with both. BTW, can I include more NI-VISA queries in parallel in LabVIEW?) 

Thanks

[Dennis_Knutson · Accepted solution]

No, you cannot use a daq device to simulate a serial port.

I don't have a specific recommendation for a vendor but I've had much better luck with adapters built with a chip from ftdi than from others. Google 'usb to serial adapter'.

You can have multiple communication threads with multiple adapters.

[jeanlucpicard]

Okay, then I should proceed with the adapters. With these I had a bit difficulty:  I find plenty of devices which support USB to UART RS232 (based on FT232RL and FT232RQ chips), however I guess, that these are not suitable for my needs. Am I right?

[Dennis_Knutson]

No, you are not right. Why do you think the ftdi chips you mention are not suitable? What sort of 'difficulty' do you have?

[jeanlucpicard]

The main difficulty is that I am not familiar with these devices. I thought it was not suitable because all the pages say that cables based on these chips are for 3v3 to 5v connections between an arduino and a pc, while there are some more expensive cables which do not mention uart or 3v3 connection.

Should I worry about this or can I go on with these chips?

[Dennis_Knutson]

If you buy a cable that says it is USB-RS232 compatible, then you are okay. The voltage levels of the chip itself is level shifted. Look at the specs for the assembly for compatibility.

[jeanlucpicard]

Okay, thanks 🙂