>. Am I supposed to use some current limiting resistor on the led?

YES. The problem you are seeing is that the voltage on output pin is
dropping to the level of the LEDs forward voltage (Typically 1.5V-2V). A
suitable series current limiting resistor will ensure that the output pin
voltage remains at 5V, which can then be used to drive the next stage
succesfully.

Ian Rozowsky
Engineering Manager
Centurion Systems
P.O. Box 506
Cramerview 2060
South Africa
Tel   : +27-11-462-4499
Fax   : +27-11-704-3412
e-mail: roz@centsys.co.za
web: http://www.centsys.co.za

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