Constant Voltage output via USB

[Jeff G]

I am attempting to control a home-made constant wattage power supply using USB.  The power is set by a voltage input (via the output channel of the USB) that is of the same magnitude as the desired power.  How can I use LabVIEW to get a constant voltage output over the correct USB channel?

I have used LabVIEW with GPIB a bit, but I haven't the faintest idea what to do when it comes to USB.

Thanks for any help you can give me!

[Dennis_Knutson]

USB doesn't work that way. A USB device sends and receives a digital bit stream and not varying analog voltages. Check the specs for USB at http://www.usb.org/developers/docs/. There are development kits available that help you get started with USB communication.

[Jeff G]

One of my professors pointed me to a website (USB in a Nutshell) and that was one of the first things that was explained.  I am still not clear on how to communicate with a device using USB and LabVIEW, but the constant voltage output is definitely not going to work.

[tbob]

To put out a constant voltage, you need some type of equipment, like a power supply.  Are you trying to communicate with the power supply through USB?  Or maybe you just want to set the USB data line high all the time?  Explain more.

[Dennis_Knutson]

About all I can say is that some of my co-workers developed some USB boards around the Cypress AN2131QC (EZ-USB) chip.

[Bruno_Cesar]

Hello all,

Do you know if there is a way to set the USB data line high or low, using LabVIEW? Maybe by calling a DLL or something.

I intend to use it as a single digital line. I does not have parallel or serial port available.

Please, if someone knows how to do it, let me know.

Thanks in advance.

[Dennis_Knutson]

I don't know if you can do anything on the USB without a device actually connected to it. The LabVIEW VISA functions require that but maybe there is a very low level windows function you can call. If there is, I would suspect that you couldn't have any other USB devices like a mouse or keyboard attached. The USB org at the likn above has a forum and you would probably get an answer there.

You could also just buy an inexpensive USB-RS232 converter. They cost around $20-$25. You could even get a chip from http://www.ftdichip.com/FTProducts.htm and make you own.

[tbob]

Trying to use a USB port to perform the function of a digital output is going to be difficult.  Your best bet would be to buy a USB-DIO.  Measurement Computing makes one for $99 I believe.  Works right out of the box and comes with Labview drivers.  Look at their website for the USB-1024LS or the USB-DIO24/37:

 http://www.measurementcomputing.com/cbicatalog/directory.asp?dept%5Fid=415&top%5Fid=403&dept%5Fname=...