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Configuring the Digital Output in the USB 6009

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I have a USB 6009 DAQ card. It appears that the when the DAQ card is powered up, it always defaults to a digital output signal of 'High' or 'Floating'. I want it default to 'Low'. Is there some setting that will allow me to "program" the DAQ device to have all outputs set to low when powered on? Right now I have to manually go into MAX and set the output to 'low'. Thank you very much for your help. 

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In a nutshell no.  The 6009 is designed as an ultra low cost device.  It does not have programable power-up states or many other features available to more costly devices.  The device will power up with all digital pins floating (internal pullup to 5VDC through 100K Ohms)

 

You could place all outputs low byu hacking in through NI Device monitor but, then no other program would be able to access the device.  If you must power up with a low on all pins you need a solution in hardware.  Either a different device or some signal conditioning.


"Should be" isn't "Is" -Jay
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Jeff...Thanks a lot for your prompt and detailed response. Appreciate it. 

I researched further on this and one of the solutions to override the default digital high is through the use of a resistor. What I am told is I could place a 10k resistor between the specific digital output and the ground on the digital terminal block. That will prevent that particular digital outputs to go high by default. I will have to verify how this goes. 

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The internal pull-up resistor in the USB-6009 is 4700 ohms. Connecting a 10000 ohm resistor to ground will result in 3.4 V at the terminal.  This is still High!

 

To get the input below 0.8 V (to guarantee that connected devices will see it as low) you must use a smaller resistor.  The largest standard resistor which will get the voltage below 0.8 is 820 ohms (nominal V = 0.743 V).  This will draw about 6.1 mA of the 8.5 mA capability of the device so the current drawn by any load must be less than the difference.  You must configure the output for active drive (push-pull) or the output will always stay low.

 

Lynn

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@johnsold wrote:

The internal pull-up resistor in the USB-6009 is 4700 ohms. Connecting a 10000 ohm resistor to ground will result in 3.4 V at the terminal.  This is still High!

 

To get the input below 0.8 V (to guarantee that connected devices will see it as low) you must use a smaller resistor.  The largest standard resistor which will get the voltage below 0.8 is 820 ohms (nominal V = 0.743 V).  This will draw about 6.1 mA of the 8.5 mA capability of the device so the current drawn by any load must be less than the difference.  You must configure the output for active drive (push-pull) or the output will always stay low.

 

Lynn


Please do read the device spec for the 6009.  (Lynn is not someone I choose to argue with without facts but 4.7kOhms seems a bit "Stiff" for the device's rated output current as I remember it, I may be wrong - really it does happen!)


"Should be" isn't "Is" -Jay
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Jeff,

 

I had the USB-600x documentation open when I wrote that.  I do not know who decided to use that value for pull-up, but it was probably the same @%#!$%#$! who designed the analog input with 144000 ohms to 1.4 V.  Those two design choices have little if anything to do with keeping the cost down but do a lot to reduce the value of the devices.

 

Lynn

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What's been said is correct - there's a 4.7kΩ pull-up resistor at each digital line. 


When the device initializes, it defaults to All-Input and the pullup brings everything high. 

 

Use an inverter, SN7404 or similar, to invert the output if a high on init is hazardous.

 

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Isn't the resistor value of 820ohm a little too low...meaning that it is going to be pulling down the output pretty hard and therefore take a lot of effort (current) to pull it back up. Do you still think this is the way to go? I have to put these resistors across 6 of the digital outputs I am using to turn high from low, in a programmed sequence. The default/initialized high is what I want to overcome. Thank you so much for your guidance. - Sid

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Lynn:

 

I think some one has been listening to our gripes! I just came across a new product announcement for the USB-6000. >1Meg analog input impedance (only 10Ks/s), digital outputs are pulled low.

 

http://www.ni.com/pdf/manuals/374113a.pdf

 

I was quite impressed by this offering from DataQ, $149 only 4 differential analog ins (however +/-2.5V to 50V ranges), and the specs on the voltage and current rating of the digital I/O and pretty solid. Same price as the USB-6000, Would be nice if NI could offer such I/O ranges on the low end (and other) devices.

 

http://www.dataq.com/support/documentation/pdf/datasheets/di-155ds-usb-data-acquisition.pdf

 

-AK2DM

 

 

~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
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Solution
Accepted by topic author Sid05

Sid05,

 

Yes, 820 ohms is low. Unfortunately the way the device is built, that is about the only choice you have without building external circuitry such as SnowMule suggested.

 

AK2DM,

 

Thanks for pointing out the USB-6000. At last a real, if limited, DAQ device.  Too bad it only has 4 DIO lines.

 

Lynn

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