Why can i not get elvis DIO to turn on an LED?

[PCM]

I have been tring to bypass elvis and have my DAQ (USB-6251) write directly to the ELVIS DIO pins (I want to be able to write fastr than ELVIS alows).  I an so far unsuccesful.  So I thaoght I would try a digital write using the DIO writer and reader.  This works fine, the DO pin can write to a DI pin and ELVIS is happy.  But when I connect the DO to an LED it will not light.  When I measure the voltage with the ELVIS DMM the voltage measured is only mV and not the expected 5volts.  The ELVIS DI reader will see a high level DO but as sonn as I connect the meter the DO sees a low voltage level.

[Broken_Arrow]

I'm not familiar with the ELVIS system, but check/consider these things:

1) You are hooking up a DIO (in this case an Out) directly to an LED? Check the current capability of the digital out. You may need a driver chip to light the led - maybe ELVIS uses drive chips or TTL buffers to boost the current of the incomming DIO's.

2) Do you have a valid return path, i.e. is the GND refernce on the LED the same as the GND reference of the DIO. If you are only measuring in the mV, then this could be the case.

3) Assuming you do have enough current, then consider the resistor you have hooked up to the LED (330 ohms would be good). Observe polarity of your LED, etc.

# 2 and 3 are sort of "stating the obvious"