NI435x DIO input lines won't work with a pull-up resistor

[JAH 312]

Hi,
I'm using an NI4351 PCI DAQ card with the Ni435xn driver and LabWindows/CVI v5.5 (on Windows 98) to digitally control a power supply unit (PSU). The connections are made from a TBX-68T terminal block. The PSU generates a logic high (> 4.3V) under 'current overload' conditions and I want to capture this event by polling one of the DIO port lines configured as an input through software. Any DIO line 'latches' high when I momentarily connect it directly to 5V and 'latches' low when I momentarily connect it directly to ground. However these logic states don't change if I connect a DIO line to 5V or gnd via a pull-up/pull-down resistor (even 4.7Kohm). The PSU uses a FET switch connected to 5V via a 10Kohm pull-up
resistor to generate the current overload signal. The FET switches on for a logic low output and off for a logic high output (via the 10Kohm pull-up). According to the manual, the maximum specified input current drawn by each DIO line is 10uA @ 5V, so I don't think the 10Kohm pull-up should cause a problem. Furthermore, a logic high is read as >= 2V. I would be grateful for any ideas on how to successfully read >= 4.3V through the 10K resistor as logic high, when the PSU FET is switched off.
Thanks.

[dhuff]

It sounds like you need some sort of buffer or trigger signal, one that will isolate your pull-up circuit from the DIO lines. I would recommend a Schmitt Trigger circuit, or possibly using a 7404 inverter.

A Schmitt trigger is a comparator circuit, if the input goes high, the output switches high until the input goes below the low input level. Since the circuit uses external resistors, you can use variable resistors to tweak the circuit to your liking.
check the following link, or do a web search for information <>

A 7404 inverter is essentially the same idea, except it is done using standard TTL or similar voltage levels. The resistors are internal to the chip, and are not changeable. The exa
ct trigger levels will depend on the chip type. The problem is that the signal out of the inverter is inverted, (5v in gives 0v out), so if you run the digital signal thru 2 gates it comes out OK. (there are usually 6 inverter gates on each 7404 chip so you only need 1 chip)
check the link for a desription, or do a web search. <>

[hemantbhati]

Sir I want to interfacing stepper motor by NI 4351.... but MAX is not detecting the device...please guide in this regard....

[hemantbhati]

Sir I want to interfacing stepper motor by NI 4351.... but MAX is not detecting the device...please guide in this regard....

[Ed W]

Hi hemantbhati,

Thank you for posting to the NI forums.  Does Windows Device Manager recognize the device?  If not, then there may be something wrong with either your device or your PCI slots.  I would recommend changing the slot where the device is inserted.  If this doesn’t make a difference, try the device in a different computer. 

If Windows does recognize the device, then what version of the Traditional DAQ driver are you using?   Depending on your operating system, you may be able to upgrade your driver, which often resolves these types of problems.  The driver download page for PCI/PXI devices, including the NI 4351, is located below.

NI-DAQ Driver Support

Best regards,

Ed W.

Applications Engineer
National Instruments

[hemantbhati]

Sir we are using labview 7.1 and our window is xp .....we are getting the digital output from the NI4351 but we are not able to produce the data continuously to run the stepper motor i.e .( 09 05 06 0A) for the clockwise rotation.....I want a program for motor running...

thanking you for nice reply.....

waitng for the next reply....

[Abhinav T]

Hi,

Please see the following post of the 4351 and stepper motor control.

http://forums.ni.com/ni/board/message?board.id=250&message.id=29683#M29683