Serial in (RX) intermittent on Arduino clone

Forum 2005-2010 (read only) Hardware Development
1

Hello

I've built an Arduino clone and all seems well apart from serial in on the RX pin appears intermittent (activity registered but garbled data) or non-functioning at all in some contexts (using a MIDI library). The odd thing is if I wire up my Duemilanove with same hardware and running same sketch all is well.

Is there something about the RX pin that my clone is missing? Pics attached.

Thanks
Jim

2

I wired up a new Arduino on breadboard to double check it wasn't a short or continuity error with my DIY board ... same problem!

I've looked at various schematics and board layouts (clones and official boards) and the RX pin goes direct to a wire pad, nothing fancy at all, just like my board.

At a loss ... anybody?

3

Needed 1k resistor between +5VDC and pin 0. See post here

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1294803960/0

4

You wouldn't normally need a pullup resistor on the RX pin, what's connected to it at the other end?

Rob

5

The output pin of a 4N25 opto-isolator that's part of a MIDI interface

6

The output pin of a 4N25 opto-isolator

That's why you need the resistor then as the opto OP is open collector, it either pulls low or is floating, so you need something to pull the line up.

It worked with a normal Arduino because there is a 1k resistor to the OP of the FTDI chip which will idle high, therefore you effectively have a pulll up resistor.

Rob

7

Thank you so much! That's great