USB-6008 digital output (TTL) to control balloon-type valves

[Tredude]

Hello,

I am trying to build an application which controls the state (inflated v deflated) of two balloon-type valves using this external device:

Product information - http://www.rudolphkc.com/pdf/691112%201208%20G.pdf

Service manual - http://www.rudolphkc.com/pdf/691113%200902%20H.pdf

When I open the test-panel in MAX, I am able to output a TTL signal to the external balloon-controller. However, the LED indicator corresponding to each balloon lights up briefly, and gradually dissapates over a few seconds. Then, if I switch the digital output off and on again, nothing happens. When I turn the external balloon-controller off for a few moments, and then back on again, the TLL output lights up the LED indicator briefly and then dissapates.

Is the USB-6008 device capable of generating a TTL output to the external device with enough current? Or must I use some external circuitry to successfully actuate the balloon-controller? I would have thought that the spes of the 6008 (capacity to sink 0.6mA without external pull-up resistor) should match the signal input requirements of the balloon-controller (0.2mA per input channel)

Cheers!

Message Edited by Tredude on 10-06-2009 08:39 PM

[CWolf]

Is your USB 6008 set as open collector or active drive?  The default is open collector, and if your valves are also sinking that could be a problem.  There is a property node in LabVIEW that can be used to set whether the 6008 is sinking or sourcing.  Here is a KnowledgeBase article that shows how to set it.  Also, have you monitored the current while switching the 6008 line from low to high and turning your device off and on? 

-Christina

[Tredude]

Thank you for your reply! I have tried monitoring the current from the TTL output of the 6008, but it reads close to zero (even when switching between high and low). I tried the link you posted to the KB article, unfortunately it says that I am not authorised to view the document :-S

[CWolf]

Sorry about the link.  Try this one. 

-Christina

[AnalogKid2DigitalMan]

Christina:

Please correct me if I am wrong, but I think the 6008 is strictly open-collector. It is the 6009 that you can select open-collector or active drive. Link to the 6008/6009 manual:

http://www.ni.com/pdf/manuals/371303l.pdf

-AK2DM

[AnalogKid2DigitalMan]

Tredude:

Do you have a connection between the DAQ digital I/O GND and the valve controller ground (common)?

-AK2DM

[Tredude]

Yes I do, I have the GND of the DAQ DIO connected to the common ground of the valve controller.

Should I look at putting a pull-up resistor on the digital output line?

[CWolf]

AK2DM:

Thanks for pointing that out.  You are correct.  The 6008 is strictly open collector. 

Tredude:

Yes, you will need to add a pull-up resistor to the output line.  Here is a KnowledgeBase article that mau be useful to you. 

-Christina