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DAQ 3.3V TTL Output

Updated Jun 6, 2018

Reported In

Hardware

  • USB-6509
  • Digital I/O Device

Driver

  • NI-DAQmx

Issue Details

I have a National Instruments DAQ product that supports digital operations at 5 V TTL logic levels. I need to drive 3.3 V TTL. Is there anything that I can do?

Solution

Almost all of National Instruments digital DAQ products support only 5 V TTL logic, as this is the most prevalent. If you need to read 3.3 V signals as an input, you may generally directly connect the signals to the DAQ board because 5 V TTL considers anything above 2.2 V to be a logical high. However, if you are outputting signals to a device that requires 3.3 V signals, you will need to reduce the voltage. The best way to do this is to use a bus transceiver with voltage shifting, such as these:
     
    These can also be used for voltage shifting on input, should it be necessary.

    Additional Information

    There are 3.3 V devices that are 5 V tolerant. For those devices, you can directly connect the digital output without any bus transceiver. Also, both R Series and HSDIO products support 3.3 V natively.

    The PXI form factor for the NI-6509 directly pulls the 5V value from the backplane which is why it can only supply 5V.

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