Schematic Check, please

Forum 2005-2010 (read only) Software Development
1

Hello,

I am working on a schematic and humbly ask that anyone knowledgeable with schematics and/or Eagle to have a look and make suggestions before I work on the pcb layout.

The project is two arduinos with connectors on each (one also has a analog mux), one arduino sends serial to the other, the main arduino works with this data and sends to the computer.

So what I am really looking to have checked is my USB, FT232, and Arduino connections (not the connectors or mux). I made some assumptions on parts that I could leave out from the duemilanove schematic (wall power, on board programming, ICSP).

Thanks a ton for anyone willing to take a look!


2

How were you going to make it work with both a Mega TXD output and the FTDI TXD output connected together? I could see it working if you used a pair of diodes and a resistor (basically a diode-logic negative-logic OR gate) but unless you have some way to alternately enable either the FTDI chip or the other micro, I think you may have some problems.

3

How were you going to make it work with both a Mega TXD output and the FTDI TXD output connected together?

Thanks; I have it working on a breadboard right now, but only because I never send any serial to Mega1 from the FTDI (only send serial from the other Mega2). I mainly wanted this capability on the pcb for any problem solving - it (FTDI serial transmit) won't be connected if everything works a-o-k.

4

Any other suggestions, anyone??? Just trying to get smarter the easy way (not paying for faulty pcb protos!)

Thanks again.

5

Just a cost savings idea. I belive it's possible to use just one crystal and wire the osc out of one AVR to the osc in to the other AVR. The AVR data sheet should have examples somewhere in document.

Good luck

Lefty

6

I belive it's possible to use just one crystal

Thanks for the idea... I've seen the 'Dual Core Arduino' share a crystal in parallel, but that seemed like a pretty bad idea to me.

(http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1205243372/0)

So I would hook the crystal up to xtal1 and xtal2 (like normal) on the master, and connect xtal2 master output to xtal1 slave input?

7

...Or do I need to use the CLKO pin (Arduino digital pin 8 - PB0) and set a fuse bit?

Thanks

8

So I would hook the crystal up to xtal1 and xtal2 (like normal) on the master, and connect xtal2 master output to xtal1 slave input?

I think that is correct method, however I've never had the need to actually try it. Section 6 covers the clock options:

And the Atmel site may have simpler examples in their application documents. Not sure if the fuses have to be different for the second AVR or not. I know it can be done and have seen drawing showing such in the past somewhere, but might be better to test it on a breadboard first before committing to design. A crystal is not that expensive a component to worry about but the space savings might be worth it to you.

Lefty