Strange title, but it's not a hard question I guess. I'm about to build my first Arduino (used a MIT handyboard before) and wan't to do my own board. The idea is to be compatible with the shields, but at the same time, as on the BBB, it won`t have USB nor RS232 serial interface, just TTL and I plan to use a cell phone cable to connect to the PC.
My only question (so far...more coming i'm sure) is:
"Can I connect RX/TX leds directly to the Arduino pins?"
I couldn´t find any implementation of this, on the RS232 boards, the Leds are handled from the PC side (Rx) or through the transistor (Tx) and on the USB versions the use the USB chip specific pins for the leds.
I can figure out why it shouldn´t work if connected directly, the leds should drawn more than 10 mA with the right resistors.... I guess.
There is an idea here, tested and working (Mr. BroHogan):
Is there a specific reason you want to do your own board? You could just buy one of the bare PCBs from a dealer like nkcelectronics.com or fundamentallogic.com, and steal the pads from the MAX232 area to mount your LEDs.
Putting an LED on the Tx line should definitely be okay, but whether it will work on the Rx side depends on what's driving it. If it's a cellphone cable, there's a good chance it doesn't have enough current sink capability to run the LED and provide a clean digital signal, because a cellphone would only need a small number of microAmps of digital input drive.
Thanks for the answers!
I pretend to do my own board for two reasons, one is becasue I live outside the US and prefer to avoid having to wait for the mail (but I reconsidering this...) and the second is to adapt the board to my needs ( I would like to add a socket for my bluesnirf module and add a connector por the cell phone cable.
Maybe I will ahve to add a couple of transistors if I want the leds to run ok.
I would recommend that you use some low current LEDs and then you will get an indication with only drawing 1mA of current (or less if you want it not so bright)
There are many distributors outside the U.S., if that's your main concern.
Since I am in the US, I don't really know who's good among them, but I'm sure you'll get answers from their customers if you ask.