DAQCARD AI-16XE-50 software trigger OR Alternative solution?

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I've created a completed, debugged and working two channel analog input chart recording .VI that also outputs a raw ascii data file and a .LAS format data file.  I'm using Traditional NIDAQ 6.9.3 and Labview 6.1 running on a ruggudized touchscreen laptop under Windows XP operating system and using a DAQCARD AI-16XE-50. .  Everything is perfect EXCEPT

   the DAQCARD lacks analog triggering and despite hours and hours of trying; I just can't get  a digital software trigger to work.  If only someone could tell me how to configure an example .VI such as   Acquire N Multi Analog Software Trig.vi I would be extremely gateful.  I have been able to have this digital trigger example run  with only a timeout error using Trigger Channel PFI7 connected to Pin 38 of an SCB-68 breakout box.  This pin imust be connected to a single pole on/off switch feeding a Max6816 CMOS debouncing switch that outputs the TTL level +5 Volt waveform. It just doesn't trigger and acquire data from the analog input channels.

   Note:  the debouncing circuit works fine, but pin 38 on the breakout box has a + 5 Volt signal whether the switch is connected or not.  I just don't know if I'm missing something in MAX digital channel configuration or should be using DIO lines etc. The AI Read .vi  doesn't contain the configuration data for trigger channel etc. I would expect when it is running; but again there are no errors.  What are the proper setup values for this  Acquire N Multi Analog Software Trig.vi example and what trigger channel should a person use with the DAQCARD AI-16XE-50?

 I could post and share my .VI if someone might help complete this .VI   Thanks in advance.

[F._Schubert]

This card only supports digital triggering. The newer card (M Series 6281) supports analog triggering (but the ADC for analog triggering is 10 bit and not the 18 bit of the main ADC).

For digital triggering, you can use any of the PFI terminals and route it to the trigger logic. But I'm not sure how this would be done in Traditional DAQ (I'm only using DAQmx). There also is a default assignment of the PFI terminals.

Felix 

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Thankyou.  I realize that the DAQCARD AI-16XE-50 does not support analog hardware triggering; and so am trying digital triggering and using something like the PFI7 line.  Am I missing something in Traditional MAX 2.2  and/or manually configuring some of the code in an example like  Acquire N  Multi Analog Software Trig.vi.  Hints are much appreciated.

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With my switch circuit disconnected from the PFI7 line (pin 38 on SCB-68 breakout box);  why would there still be a 4.90 Volt signal on pin 38?

[F._Schubert]

Just a guess: There is an internal pull-up resistor. (alternatively, a pull-down resistor would result in 0 V). Check the documentation about this.

Felix

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Thankyou.  The DAQCARD AI-16Xe-50 user manual talks about a 50K ohm pu for Bias (pullup resistor) for the PFI7 (SCANCLK) line.  Does this mean I might add a 50K resistor between DGND and the pin 38 (PFI7). ?  How would that "pull-up" a line that already seems to have a nominal +5 Volts on it.  Please excuse my electronics knowledge shortcomings.  I try not to "tune for maximum smoke". 

[F._Schubert]

The pull-up resistor is already internally connected to the 5V, so if the pin is not connected to anything, it will be pulled up to 5V throw a small current flowing through that resistor. You can easily calculated the limits of the current: I=U/R=5V/50kOhm=0.1mA. This is done to have a defined state (low/high), as CMOS circuits might get destroyed in an undefined state (both complementary MOS-FETs conducting).

If you now place the same 50 kOhm between pin and ground externally, you would get a level of 2.5 V at the pin and this would give you an undefined state, hence a good candidate for 'maximum smoke'. If you place a smaller resistor, such that the voltage devisor would give you a low (lets say 0.5 V -> use about 5kOhm) you should have a safe pull-down configuration (I have already sean recommended values in an NI manual).

So, that's electronics for today. It only explains why you see +5V on the pin if it isn't connected. You most propably never need to change it to a pul-down configuration.

Back to the main problem, you need to assign the terminal (PFI7 or any other PFI) to AI Start (this is the start trigger for analog input).

Felix

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Excellent explanation.  I think I'll even be able to understand it.  I've  posted a NI .vi example (filled in with my parameters as best I can) in a seperate post.  This is in case someone can pick out further code problems; in addition to what is now an obvious hardware resistor problem in my electronics.  A sincere thankyou.  

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Just thinking

  Is there any reason a person couldn't tempoarily use a single pole switch between pins 38 and the DGND pin; in order to test the digital triggering.  When the switch is open there should be an open circuit and the PFI7 would be high.  With the switch closed the resistance should be near zero and the line should be pulled down to near zero volts.  I'd temporarily put up with any extra samples caused by any momentary bouncing of the switch contact .

  My guess is that in my actual debounced switch  (using the Maxim MAX6816 integrated circuit) that the output has a very high "output resistance" and that the +5V on the PFI7 line never changes state even when the Max6816 output is connected to the DAQCARD.  Am I possibly on the right track; and will have to eventually add a 5K pulldown resistor to my final switch circuitry.

  If so; you have taught me more about this subject than I have learned in 60 years of electronics tinkering.  Best wishes. 

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I created another thread "Can Anyone Successfuly run this .vi".  (basically an adapted NI example ofAcquire N Multi-Digital-Trig.vi).  With some time and maybe luck it seems to work fine and is posted within the above named thread.   No one seems to have ever come up with this particular solution; at least they have apparently never posted it to the WEB.  I  tested it with a SPST (single pole single throw) switch connected to PFI7 pin 38 and DGND pin 39.; and it successfully controls analog data acquisition from two channels on the DAQCARD AI-16XE-50.

  Now that this works I should only have the implementation of the Maxim 6816 debounce switch chip in place of the SPST switch used in this test .vi.   Unfortunately  the MAX6816 (being a CMOS output) is not directly compatible with the TTL levels of the PFI7 line.  Could I again impose on the readers of this forum to offer up your hints and solutions to this interface problem.  Thanks