Quote:
Originally Posted by Al Skierkiewicz
Keith,
There are a few other threads were this is discussed. The DIO comes directly from the NI digital module that is speced at +/- 2ma and is pulled up to +5 on the DSC through a 10k resistor.
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This is a fine point I reckon (and a very understandable mis-interpretation) but my advice comes from a detailed reading of the NI 9403 spec. The DSC is NOT strictly spec-ed for 2mA per DIO output. The DIO channels on the DSC are directly connected to the 9403. The 9403 is spec-ed for 64mA total on 32 channels and TEST data shows 4.4V out when driving a 2mA load (on a single channel). It does NOT say that sinking more than 2mA will drive a single channel into over-current protection mode. And this type of spec is pretty typical. Page 8 of the NI 9403 Operating Instructions and Specifications shows an example driving an LED. So one can drive a few very high-efficiency LEDs (2-5mA) and be careful not to exceed the total 64mA. I have a few chip LEDs on a board laying around, tried this real quick and it works fine.
DIO is not the best way to go though. I would not recommend a team w/o an EE mentor use the DIO channels for LEDs. The solenoid outputs or relays or custom circuits are better choices. For example, it would be easy to drive scores of LEDS with some I2C high-current latches.
HTH