Hi Dave,


thanks for your concern,

the voltage drop across the LED is an important issue here. if the voltage different across the LED is '0" then the LEd cannot be lighted up. a resistor in serial with the LED is to protect the LED when the high pulse current flowing through the LEd aND TO PROTECT THE PIC FROM HIGH IN PUT CURENT . so we do have to consider the voltage drop on the resistor.

in this case the positive pin of the LED is 1.65V, then the negative pin of the LED has to be '0' as set up. however the situation different, both side of the LED is 1.65 so it means that either open circuit (no current flowS through the LED) , the bad PIC or the program not well set up( i.e conf, ...).

I wish getting some suggestion , ideal from you,

thank agian