Analogue output with NI USB 6009

[lmateos]

Hi  everyone, 

i am using USB 6009 to generate a voltage to 5 identical LEDs in parallel. i need the value of the current to be canstant at about 150mA.

anybody knows how to set the current to a certain value?

thanks 🙂

[Kevin_Price]

A 6009 isn't made to generate constant current.  It also isn't capable of sourcing 150 mA per output channel.  At minimum, you'll need alternative or additional hardware. A quick search shows that LED drivers are readily and cheaply available.

-Kevin P

[F.Morandat]

Hi Imateos,

See the datasheet http://www.ni.com/datasheet/pdf/en/ds-218, the output current drive of the USB-6009 is 5mA.

For 150 mA, you can use a stabilized current generator or contact the NI commercial service to help you to find the product the more suitable for your needs.

[loubnaDZ]

Hi Kevin, thanks for your reply. 

I need to control the voltage across the LEDs to use it for PID temperature controller. Each LED needs a voltage of about 5v and current of 30 mA. I don't think I can use LED drive as the voltage across the LEDs can not be controlled through labview in that case as far as I understood. If not, can u please guide me to a way of doing it? 

Thanks 🙂 

[loubnaDZ]

Hi Morandat, 

thanks for your reply. 

I can't use a current generator as I need to control the value of the voltage across the LEDs through labview. Can you please further explain that if it is possible? 

Thanks for your help. 

[Kevin_Price]

Well, PID control is quite a different need than constant 150 mA current.  You're still gonna need some kind of other hardware to source your current.  There are probably many options but I don't have any particular expertise for guiding you on that part.  Hopefully others will chime in here with more useful advice.

The other thing worth mentioning is that USB is not typically a good choice as a platform for a software control loop due to latency and variable timing.  You might be ok for temperature control though, especially if your control loops can run in the <10 Hz realm.  (Number is an educated guess, not a known hard limit.)

-Kevin P

[loubnaDZ]

Hi Kevin, 

thanks for your help and for all the information provided. If the USB is not a good control system, is there any alternative that functionalises similar the USB 6009 but provide a good control? 

Thanks, 

[Kevin_Price]

There are other options, from desktop MIO boards to cRIO and more.  And there are many tradeoffs -- budget, timeline, capability, learning curve, etc.

USB might work for you if your system response is slow and your control limits aren't too tight.  You'd get significant improvement in latency with a desktop MIO board, but still have some timing variability under Windows.  A cRIO system would be more costly and have more learning curve, but you could get more consistent loop timing.  Either of those will (likely) still require external hardware to source the current you need.

It may be good to focus first on finding off-the-shelf devices that are designed to source current and be controllable.  I'm afraid I don't know the field at all really, and can't point you toward anything specific.  Maybe someone else here has some good ideas?

-Kevin P

anyone?  anyone?  Bueller?