Pull up Resistors Rx, Tx on MCU

Thread Starter


Joined Jul 6, 2023

I want to add to design LED indication for Rx, Tx over pull up resistors, please refer picture for more detail.

I do not know is this good idea or is better to add two dedicated outputs on MCU only for RX, Tx LED management.

Please share pros and coins for solution on picture.



Joined Aug 27, 2009
Sure, a separate driver gives you external indicator options but I wouldn't say you can't do it with the right leds if all you need is a PCB indicator.
I use the tiny 0603/0805 low-current SMD leds for direct to pin rx/tx logic indicators as most proper receiver modules and devices have Schmitt trigger inputs. The 1-2mA drive requirement (adjust the current limiting resistors appropriately) is well within most I/O port drive current sink specifications (the MAX chip MCU I/O can easily sink 30mA and still meet proper logic levels). It's common to see i2c pullups in the 2K range for bit-banged gpio, well within the range of low-current led limiting resistors.
Last edited: