How do I power an RS232-port device through a DAQ device?

[hyenah]

I am a student attempting to connect a digital thermistor to a NI USB DAQ device through its screw terminals and analyze its data using SignalExpress. The thermistor has a 9-pin RS-232 adapter that is designed to be powered through the RS-232 port on a PC, but I am unsure how to power it through the DAQ device. Currently I have wired the RS-232 adapter's ground, transmit data, and receive data pins to the DAQ device's screw terminals, and done "handshake looping" (by shorting pins 7 and 8, and shorting 1,4,6).  SignalExpress and MAX cannot acquire any data signals, and I believe that the problem is that the RS-232 adapter isn't getting powered.

Is it possible to power the adapter through the DAQ device? Is there some other way to power the RS-232 so that I can keep my other connections the same? I can't connect the adapter directly into my laptop because it doesn't have a RS-232 port, so I was hoping to get the thermistor data (along with that from other instruments) through the USB DAQ device to analyze.

Thanks!

[Dennis_Knutson]

Do I understand you correctly? You are trying to acquire data from an RS-232 device with a DAQ board? Powering the port is going to be the least of your problems. One, the voltage levels of RS-232 are not compatible with the TTL levels of the digital I/O of any NI DAQ board. Two, the timing requirements of RS-232 would require you do a lot of custom programming. That's if the digital I/O of the DAQ device is even capable of it. You don't mention which board you are using. If it's got static ditial I/O, forget about it. Even if you had power to the serial instrument, MAX would not recognize a serial device and neither would Signal Express.

A USB->RS-232 converter is pretty cheap. I've seen them range from $15-$25.

[hyenah]

Oh...okay. Sorry, like I said, I am a student and am just learning how to do DAQ. There seems to be an impressive collection of knowledge on these forums; could someone perhaps advise me on the setup?

I've been trying to figure out if I can still use SignalExpress if I get a RS232-USB converter; I'm still looking at how I might set up the step for something that doesn't go through the DAQ device. Just to check, I have another hardware component that outputs voltage. I hope that it is more straightforward to connect to my DAQ device (USB-6211). Is there anything not obvious that I should watch out for when connecting this? I checked the voltage input limits that is specified for the USB-6211, and my hardware component will be within that limit.

Thanks a lot for your help.

[Dennis_Knutson]

I've not used Signal Express. You can check the answer by Ebele in this post for information on how to create a custom step in LabVIEW and import it into Signal Express. You might have to do this for your serial instrument. The voltage measurement with the 6211 should be very straight forward.

[hyenah]

Thanks, I'm looking at the various links right now. I'm somewhat familiar with LabVIEW and have access to it on school computers, but I don't have it on the laptop on which I'm developing my project. It seems like in order to call a VI in SignalExpress, LabVIEW may have to be installed on the same computer; does anyone know if this is true? Otherwise, I might be able to create a VI on another computer, using the appropriate COM ports, and import it as a user-defined step in SignalExpress...

[Chris_R.]

Hi hyenah,

You do not have to have a development system of LabVIEW installed on the computer you are using user defined steps with Signal Express.  The LabVIEW Runtime Engine is required if you do not have LabVIEW installed.  Make sure you use the same version of the Runtime Engine as the version of LabVIEW the VI was created in.  Of course you will need LabVIEW to create the VI, but that can be done on a different computer.  

Have a great day!

[hyenah]

Is it true that I will need to develop the VI on LabVIEW 7.1 or later in order to create a user-defined step VI for SignalExpress?

[Chris_R.]

Hi hyenah,

Yes, that is correct as stated in the KnowledgeBase linked above.