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Topic: Looking for the cheapest USB-Serial (TTL) around (Read 4553 times) previous topic - next topic


Aug 19, 2010, 08:41 pm Last Edit: Aug 19, 2010, 08:44 pm by Tchnclfl Reason: 1
Well, my little home-made Nokia USB-TTL cable looks like it finally gave out on me, and I'm looking for a replacement.

What I want is the cheapest USB-TTL cable/board available.  So far it seems to be Modern Device's USB BUB coming in at $14 + shipping (~3-4 bucks).

Are there any cheaper than this?  Please don't suggest the $3 Nokia cable again, I just don't have the patience for the drivers, etc.  It took over an hour last time just to get the drivers straight, and to top it all of my cable didn't have an internal wire for +5V...

Anything and everything is helpful :).  As a side note, I'll trade a new MSP430 launchpad + cash in as a trade for a good one if anyone wants to :P.


Aug 19, 2010, 08:45 pm Last Edit: Aug 19, 2010, 08:45 pm by kg4wsv Reason: 1
Hmm, you say
What I want is the cheapest USB-TTL cable/board available

then you say
I'll trade a new MSP430 launchpad

so, why not toss the MSP430 chip and use the USB/rs232 on the launchpad?  I mean, you've already got it, so it's cheap, right?



Aug 19, 2010, 08:50 pm Last Edit: Aug 19, 2010, 08:51 pm by Tchnclfl Reason: 1
Hmmm I hadn't thought of that.  Is it plausible?  I mean to say could i expect it to work?  The MSP430 board is designed as an emulator rather than just USB-UART...

[edit]Not to mention the fact that they're completely different architectures, and the MSP430 chip is completely erased and rewritten, rather than writing data without erasing the bootloader.[/edit]


Aug 19, 2010, 09:19 pm Last Edit: Aug 19, 2010, 09:20 pm by kg4wsv Reason: 1
The launchpad has a usb/rs232 chip separate from the microcontroller.  Of course, it's a TI chip, not an FTDI, but the basic architecture is the same as the arduino.

There even appears to be a dotted line, so you can hack the USB section of the PCB away from the processor section.



Aug 19, 2010, 09:45 pm Last Edit: Aug 19, 2010, 09:51 pm by Osgeld Reason: 1
already tried doesnt work

usb port <> ti usb chip <> another msp which is doing all the emulation / jtag crap <> you target chip via its own serial connection
(when you plug a launch pad in your talking to a mcu thats talking to your target mcu via its own separated (soft?) serial port )

ok so cut off the extra QFP msp chip, now you just lost clock to the ti usb chip as there is only 1 12mhz crystal on board, that goes to the other mcu, which is then piped out of a pin on that same mcu to the usb chip

ok crap, do you reprogram the ti usb chip so it will drive a crystal? or do you make a 12mhz clock source

at that point it hit the trash

if you want to get a 12mhz crystal oscillator you can cut off the larger of the 2 chips and attach it to the ti usb chip, but your soldering leads that make 30guage wirewrap look large



Hah that's what I thought :P.  Ah well, still in search :).


I use and love the USB-BUB from Modern Device.

ITead has the foca:


It's cheaper but more barebones and doesn't follow the "standard" pinout of the USB-BUB or FTDI cables have.


Hmm the foca is interesting!  I suppose I could slap a small piece of perfboard on bottom, and add my own headers fairly easily.  Plus it's TINY!


One option might be to find a cheap usb->serial cable, then hack the dongle end before the 9-pin DB connector. I've found a few such serial cables cheaply at Fry's Electronics; I've also found them dirt cheap at local Goodwill locations. I've never tried hacking them, though.

Maybe you should just break down and buy an FTDI breakout or cable and be done with it; they're not that expensive...

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


Yeah I'll probably end up getting the BUB, but I figured it might be worth looking around :P.


That foca thing does sound interesting! That's way cheaper than other breakouts I have seen, too! Thanks for posting it!


I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.



I think you should be able to pull off serial (3.6V) off of the launchpad pins labeled RXD and TXD, regardless of whether you're using the programmer section or the target chip at all.  As I understand it, the programmer/debug circuit and the "application uart" show up as separate USB devices (well, a single composite device), and normal windows utils will access the serial port just fine.  You might be out of luck if you have a mac, or linux, or vista, or W7, though.  TI's driver writers seem to be a bit behind the curve. :-(
And it'd hardly be convenient!


I'll give it a try a little later after work :P.


Aug 20, 2010, 12:21 am Last Edit: Aug 20, 2010, 12:22 am by Osgeld Reason: 1
I think you should be able to pull off serial (3.6V) off of the launchpad pins labeled RXD and TXD,

well (and I have been poking at this thing for well over a month now) the very first thing I did was jumper RXD and TXD together to form a loop back and brought it up in a serial terminal, you could send stuff to it all day long but it would never echo back

there is some voodoo going on with the TI software (which is a problem for a system) that QFP msp chip has multiple functions and I believe that unless you address it and tell it "yo be a serial port" it isnt going to be, its default state is the emulator, similarly its default programming seems to be jtag and not serial

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