Nokia USB Cable Is USB-to-Serial In Disguise

[Jethomson] worked out a way to use a Nokia USB cable at a USB to Serial cable. He was able to pick up one of these cables for less than $3 delivered. A little probing worked out which conductors go with the appropriate signals and from there he developed a way to protect the 3.3v signal levels with a voltage divider.

It’s not surprising that this works, having seen [Will O’Brien’s] post covering serial communications on Nokia phones. In that post we learned that the Nokia phones are using TTL communications. Once you’ve completed [Jethomson’s] modifications to the cable you can follow his examples for using this in conjunction with an Arduino.

43 thoughts on “Nokia USB Cable Is USB-to-Serial In Disguise

  1. another good place to source these are old pda stands, I had (evil laugh) a Compaq areo (or whatever) and I noticed that the “usb” connection was only transfering serial speeds

    in the little catalog I noticed the usb dock was optional, so bingo!

    anyway, if your too cheap for 3 bucks and shipping maybe a buck at the thrift store will yield good results

  2. @osgeld, that’s cool. Good to know.

    I wrote this article. I synthesized a few HOWTOs for adding a serial port to your router. Nowhere in the article do I say anything dumb like USB-to-FTDI. The poster came up with that title. I may call it USB to TTL, but that’s not strictly correct. It is a USB to Serial with 3.3V levels but works with 5V signaling. It doesn’t do everything an FTDI cable can , but if all you need is RxD and TxD (and DTR if you work for it) then this cable is good enough.

    @fdsa, Maybe you don’t mind paying $20 for an FTDI cable, but I’m sure others would like to save a few bucks.

    @Pete, That’s a good price. A BUB board from Modern Device is even cheaper. But I think you’ll agree if you want to leave the cable permanently attached to your project $3 is better.

  3. @jthomson

    I was not referring to your article but to this blog post. I’m quite familiar with FTDI’s chips, which is why I immediately read your article to confirm that it wasn’t an FTDI part (the voltage divider gave it away). Bad hackaday!

    For those less knowledgeable, the 3.3v FTDI TTL asynchronous serial and multi-mode chips are 5v input tolerant (at least for every chip that I used). 3.3v is also above the “1” level for 5v TTL logic, so using a 3.3v TTL FTDI chip to talk to a 5v part is OK! I abuse a FTDI 3.3v breakout cable like this at least once a week on random parts and have never had a problem. jthomson’s hack by adding a voltage divider to 5v intolerant parts is a classic technique, and one that works quite well.

    I’m a big fan of FTDI chips because of the functionality and reliability. That said, simple USB based serial connections are best with a PL-2303. They’re quite effective, well supported, and dirt cheap.

  4. Also note that “FTDI” may not necessarily refer to the controller; it can reasonably refer to the particular “FTDI pinout” used by FTDI’s USB-TTL232 cables. It’s becoming something of a de-facto standard among devices with TTL-level serial ports.

  5. It surprises me a bit that so many products of this type still revert back to simple, slow serial port type communication… I wonder why they don’t just fully utilize usb? Or at least max out the serial speed (aren’t many of these usb/serial converters capable of 1Mb+ ?)

    It’s just funny that rs232 seems tagged as a ‘legacy device’, when really that’s all their doing anyway.

  6. ^ duh (they’re)… damn noreaster storm knocked out my power and now I have no coffee or shower. Eco friendly wind power was blown off the mast, and it’s not sunny enough for solar. Guess I’ll increase my carbon footprint and burn some good ol oil.

  7. @Agent420, the problem is cost, including USB connectivity natively in a microcontroller would drive up the cost notably and needlessly when external cables from places like FTDI convert TTL-USB reliably – not all microcontrollers will ever need to be regularly or constantly in connection with a PC’s USB, so an optional cable is to the manufacturers the wiser (cheaper) solution.

    And devices that do use microcontrollers that need to be connected to a PC’s USB port regularly or constantly will have usually have the necessary USB capable chips onboard for highspeed connectivity, such as mp3 players.

  8. @Agent420

    Eh? most serial protocols look like RS232, just not using those crazy signalling levels. The serial hardware in micros isn’t just for connecting to a usb uart (spi, i2c, 1-wire..) hence you don’t get usb hardware in there unless you buy a micro that is intended to be used in USB designs.

    If micros were made in the way that you’re suggesting all of your once simple serial communicating onboard hardware would need to have usb controllers embedded.

  9. ^ No, I get all that.

    I guess I’m just thinking how rs232 has been deemed kind of ‘antiquated’, having been removed as a std feature on modern pc’s, when the reality is we have simply given the emperor new clothes.

    And while I understand that not all of the low end micros have hardware usb, more and more of them do; and many of the devices using these kinds of cables are ARM level or greater, where usb could be implemented. Yet I sense that rs232 is not going away any time soon.

  10. @Agent420

    Using huge voltage swings to push data a few feet is antiquated yes.. PCs don’t have RS232 serial ports anymore, but even if they did you couldn’t wire them to a micro. An FTDI USB uart can’t drive RS232 devices without a level converter either..
    sending data serially without a clock is always going to look like what RS232 looks like, there’s no getting around that. So “RS232” won’t go away.

    FTDI do parallel devices too, and you can hack a JTAG cable out of them. Maybe that’s what you’re thinking about when you talk about ARM devices? N.B. You can get some ARM micro’s that are on the same level as ATmega, I wouldn’t being ARM based means it’s a really powerful chip.

  11. I used to think hack a day was cool, then I started reading it every day.

    Jesus, this guy brought a USB to serial cable and then used it as a USB to serial cable? Welcome to the new millenium, even if you are 10 years late.

  12. Man, you guys who have known about this forever are awesome! If only we could all be as cool as you.


    There are people out there (especially kids and students) who *don’t* know this stuff, and we should help them learn rather than being elitist tards. Some people *haven’t* been in this scene since the hacking of the WRT54GS. If you’ve seen this before, scroll to the next article. Do you complain about the evening news because it summarizes news reported earlier in the day that some people might have missed?

    If you want a blog that only reports brand new, cutting-edge hacks – start your own. So tired of your crap in comment sections that should be used for helpful discussion.

  13. @pc486
    I knew you were being helpful. I was trying to address the inaccuracies of the summary which I didn’t write. The RxD pin of certain versions of the PL2303 is 5V tolerant, so the voltage divider isn’t always necessary.

    Everything pc486 has said is clearly stated in the article. If you mean the summary, I have no argument with you.

    Your article was one of the sources I synthesized into my article. You’re in the links sections. Thank you!

    @ all those who say this old news
    It is old news for router hackers, that doesn’t mean it can’t be new to an electronics hobbyist playing with a micrcontroller. I wrote this article because I myself had a hard time finding a cheap USB to TTL cable for Arduino. I wanted to do Arduino as cheaply as possible. I only lucked on to the router articles after a lot of searching. Sometimes information gets trapped in small circles. Hack a Day will broaden that circle. A couple of bits that aren’t in the router articles are adding DTR and USB_VCC.

  14. Why not, you elitist paraquad? One persons microcosm is a pretty small sample – Common might not be the correct nomenclature. Let’s try hard to be friendly and inviting. Just because our nerd-genes has wired us to behave like anti-social ass-burgers doesn’t mean we really have to.

    On topic, I just ordered a couple of these:

    It ain’t 3 bucks, but it isn’t far off. The USB-end easily cracks open, to reveal which lead has what function.

  15. @Hitek146
    It’s not a repost. I searched the archive before submitting. Here’s a similar article:

    If you just came here to comment “Simpson’s did it!”, let me go ahead and do that for you so you don’t have to. I’m just thinking of the SNR.


    Can anyone comment on using an EEPROM to change the Configuration Descriptor MaxPower? This will make the chip report as a USB High Power Device allowing up to 500mA to be drawn. I’m looking at page 11 of the PL2303HX rev.A datasheet.

  16. > Sooo… Are we supposed to repeatedly keep reposting common knowledge every few years or so, just to make sure noobs keep informed? Just asking…

    There are so many people here that can’t grasp the simple concept that stuff is only common knowledge if you’ve been told it first.

    Once you didn’t know this obvious stuff. You weren’t born with the knowledge…

    If I ran this site I’d switch the comments to moderated mode to cut out the elitist rubbish, it’s just so unhelpful and makes us all look like selfish idiots. It’s verging on YouTube quality at times (which is almost as bad as Slashdot)…

    Surely we should encourage the ‘noobs’ so that there are more people who want to take stuff apart and void their warranties, etc. The new engineers of the future have got to come from somewhere…

  17. I wouldn’t say lame but we have been using these cables for serial connections to routers for a couple of years now, it’s not jtag but it will get you there sometimes (in a brick situation).

  18. This seems to be the oldest news posted here since hackaday started. I mean literally, not even the oldest posts at hackaday are older than the well known fact that mobile cables are nothing more (or less) than serial converters.
    Bad job at editing, seriously.

  19. The CA-42 cable is a component of a known fix for repairing faulty firmware on a series of Seagate hard drives (7200.11)

    I have used the cable and hyper-terminal to fix a couple 720.11’s so far

  20. So annoying that paypal has such horrid things in it’s user-agreement making it impossible for me to sign up, because so many nice sites with cheap gadgets insist on paypal, and so does ebay now for new users, although the EU anti-competitive people are looking into that to see if they can allow it now.
    I guess after hearing experiences people have with paypal I should be happy the ULA stops me though.

    Locally these cables run between $10 and $23 though, outrageous bastards to dare to ask more than $20 for what they buy for $2.50.

  21. maybe hackaday should start a new section “things you should know” or “common knowledge”

    @whatnot: your charged $23 because you don’t have the risk associated with paypal’s ula. how much is not dealing with paypal worth?

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