Post by thread:LED display without current limit resistors ?

Happy New Year PICLISTERs I am interfacing a PIC 16C84 to a multiplexed Common Anode 3 digit 7 segment LED display. Power for the circuit is 2 'AA' battery cells (nominal 3V). Each LED segment is rated for a maximum forward voltage of 2.8V. QUESTION: Do I really need current limiting resistors ? The individual segments are pulled down by the PIC port B outputs, which introduce some voltage drop. Each common anode is driven by a 2n3906 transistor. Its voltage drop will vary around 0.2 volts depending on how many segments are turned on. This will result in some variation in intensity, but I think I can compensate for this by varying the mux duty cycle depending on the number of segments turned on. QUESTION: Has anybody tried this ? Anything I am missing here ? Randy Howe

Randy, I am new. I mailed a letter to: spam_OUTpiclistTakeThisOuTmitvma.mit.edu titled pic damage, watchdog... Did you receive it? If yes/no, let me know. I will act accordingly. Jean