Two PCs, Two serial USBs, One Arduino, via CA-42?

I’m currently asking around about hardware debuggers for the Arduino (http://arduino.cc/forum/index.php/topic,66736.0.html) but in the meantime, I was wondering about using a second (software) serial port to output debug information (I’m planning a project that involves tying up the built in USB serial).

Of course, if the CA-42 is no good, can anyone recommend an inexpensive ttl-serial device - I’ve been scanning ebay but the huge selection and features is mind numbing…

  • Can I add a ttl-serial usb connector and use it to 'talk' to a second computer while still using the first USB as normal?

Yes you can use a second converter chip as you suggested for debugging or whatever. Most of those will work if you can locate the proper PC USB driver for it and you don't require the DTR signal for auto-reset function for uploading a sketch.

Here is a list of nice inexpensive USB ttl serial converter chips on e-bay:

http://shop.ebay.com/i.html?_trkparms=65%253A12%257C66%253A2%257C39%253A1%257C72%253A5049&rt=nc&_nkw=USB+TTL+serial&_sticky=1&_trksid=p3286.c0.m14&_sop=15&_sc=1

The CA-42 does work - I've got a bunch of them - but it is unreliable at higher baud rates (not an issue for you since you're using a soft UART).

Also, make sure you use NewSoftSerial, not the built-in SoftwareSerial: NewSoftSerial is interrupt driven and much more reliable than SoftwareSerial.

[quote author=David Pankhurst link=topic=66825.msg490527#msg490527 date=1310945348] can anyone recommend an inexpensive ttl-serial device - I've been scanning ebay but the huge selection and features is mind numbing... [/quote]

The FTDI interface used on some Arduinos is also available as a separate board, or as a cable. For example, http://www.sparkfun.com/products/9716

Thank you for the different options - esp. the links and the personal experience of the CA-42.

One other question - as long as all the grounds are connected, is there any electrical issue with connecting the two Arduino usbs (new+old) to two separate computers?

If you want to be ultra-cautious, here's what I'd do: Measure the voltage (V1) between the (unconnected) grounds of the 2 PCs -- ac + dc. Then connect the 2 grounds together via a resistor (R, approx. 1k) , and remeasure the voltage (V2). The current which will flow when the grounds are shorted together is I = (V1 * V2) / ( R * (V1 - V2) Unless it's more than a few mA, go ahead: connect the Arduino and common the grounds.

Just be sure that the 5V connections from the 2 PCs remain separated - ie. don't connect the Vcc pin on the second serial interface.

Thanks - I'll take care to check the grounds out that way