Long story short, I used a cheap ($3 on ebay delivered) Nokia CA-42 cable knockoff as a USB to serial adapter for another project (adding a serial port to a Buffalo Linkstation Live Network attached storage LINK BELOW).
Would it be possible to do something similar for use with a boarduino? Most of the cheap cables are based on a Prolific PL2303 (datasheet LINK BELOW) chipset which is supported under Windows and Linux.
Seems like a great way to get a cheap USB to 3.3V TTL...
This sounds like a good idea. I bet the prices (on ebay) will jump very soon.
It should be possible, although it looks like those are strictly 3-wire serial implementations. That means that the auto-reset feature won't work, and you'll have to push the button just like in the good old days.
If anyone is interested, I cut the end off of a CA-42 cable and discovered the following pinout:
yellow -> common
blue -> arduino TX
green -> arduino RX
red -> unknown
I downloaded the driver from Prolific's site mentioned earlier (2nd post). Version 1.0.2.5 worked for me in Vista x64. I was able to program my BBB freeduino and monitor returning serial data for debugging.
There are a couple disadvantages, the first being no 5V power to run the 'duino off of and second, you have to manually press the reset button. The second is actually a non-issue for myself as I don't like the auto-reset feature resetting my 'duino every time I start the Serial Monitor or plug in the USB cable or start the Arduino compiler. Then, there is the advantage of price, I paid just shy of $5 USD per cable shipped.
note: my cable runs at 0-3.3V on the TX line
Nice - Just ordered one from Hong Kong - $3.24 shipped.
Update: I found out that the usb end of my cable is not an injection molded plug, but with some prying I could pop it open. I then proceeded to solder the red wire to a +5V contact and behold, it now powers my Arduino too!! Now if only I could get the Arduino to bake me a cake....
For those that want the 5V power or auto-reset, you may want to look into hacking one of these: http://www.dealextreme.com/details.dx/sku.2537
$6.68 shipped
I apologize, again, for my newness. I just read this thread (thanks westfw) and the linking pages: Does that mean I would just solder the appropriate ends of this cable to... a board...somewhere? I'm confused.
Backstory: I have an arduino project, that takes Pushbutton triggers, and sends data over the USB connection. I'd like to make more, without buying separate arduinos for each ($30) or using boardino/BBB solutions with breakout USB ($20-$25)... if I can cut my Serial connectivity cost from $12-$15 to just $3, that's a big enough deal for me to do it, I just don't understand exactly what I would be connecting where...
Thanks guys,
Phil
I soldered on an end that was compatible with most of the Arduino clones out there, a BBB in my case, also compatible with the FTDI cable pinouts. See the photos, the first one is the CA-42 stock, and the second is after I have modified it.
when you say you soldered it to your BBB, where did you solder? I am a little lost there...
I soldered on an end that was compatible...
See the photos, I did not solder the cable directly to my BBB, I soldered on a connector that plugs into the 6 pin header that most people would plug their FTDI USB to TTL cable or a USB BUB into.
example of FTDI cable: http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtf8aSAtgR7DpPMdam/we00
USB BUB: http://moderndevice.com/connect.shtml
Hi
I want to clarify something....
These USB-to-Serial cables, even if they have the PL2303 chip, are they TTL compatible?
I asked because I always thought serial port specifications are not TTL compatible...
so if it is a USB-to-Serial cable, can you just connect the serial side to the Arduino? Don't we need some form of level conversion like using MAX323?
LiveRock, most of these cables (for example the one I linked in post #7) use the PL-2303 for USB , and a Maxim chip for the RS232 level conversion. The PL-2303 operates at logic levels that are compatible with the arduino pins. There is a datasheet here: http://user.chollian.net/~mines/pl2303.pdf
I wrote an article for uC Hobby with step by step instructions on how to
use one of the cables with an Arduino breadboard setup. I modified the
cable to provide USB power and auto-reset. Here's a link:
https://web.archive.org/web/20210308144706/https://www.uchobby.com/index.php/2009/10/04/diy-usb-to-serial-cable-for-3/#more-492
my hack for taking an actual PL2303 from ebay ($5 or less) and tapping into tx, rx, gnd, vcc and DTR (for reset).
yup, reset works, too. windows does not init the device ('it wont start' in windows terms) but linux sees it just fine and the IDE downloads code over this link perfectly.
unlucky for me, the DTR pin (2th down from top) did not go anywhere convenient (like a big solder pad). I had to tap onto the chip pin itself. just barely, too 
but it does work. the wire tapped on the 4th pin from the bottom is CTS and I'm not sure I need to tie that to ground but its commonly done so I did it, too.
some ebay rs232 dongles are not actual PL2303 chips but if you look carefully for ones that call it out by name, you can find them for $5 and less.
its not FTDI but its just about as good and the rest line works fine if you can find DTR or RTS.