goodbye ftdi, hello prolific

I said: "We gotta do something about these hard to obtain and pricey ftdi cables." Thanks to Jesse Welz telling me about old nokia phone cables with prolific usb to serial chip inside, and thanks to jake {jerkey} spaz for keeping it real simple with old ide cable cutups We now have $2/piece usb to serial cables at Noisebridge to use with projects like the Volksduino. Pictured below is the pinout for the prolific 2303HX, which is what I've seen used in the DKU-5 cables. It's connected to the Volksduino with an old IDE ribbon cable and a chopped IDE dual inline header with 6x2 plugs. The ribbon traces are doubled up. It fits great and is easily assembled. There's a spare Prolific pcb shown, they seem to have a little variety from part to part, but are consistent enough for someone to throw together a cable for their own Volksduino/boarduino/BBB cable in about 15-30 minutes. Prolific 2303 pinout cheapo usb-serial

Categories: General


  • Marius Kintel

    Woah, this looks nice. I’ve been looking into this as well, but got stuck on two issues. Some of you guys might be able to help me on those :)

    1) Where do you get $2 DKU-5 cables? I cannot find anything under EUR 5 here (Austria), not even in chinese eBay shops.
    2) I _can_ get hold of $2 Prolific usb-to-serial adapters (some PL2303 variant – not sure how to identify the chip under the black blob), but they all output the TTL serial inverted (active low instead of active high which is what AVR’s expect). Did you encounter smth. similar?

    Cheers from the Metalab

  • miloh

    hey Marius,

    The source for DKU-5 cables was an Ebay ‘buy it now’ auction in HK. The lowest price I have seen from ebay’s USA site is at $1.00US from China.

    As far as I can tell, the DKU-5 uses prolific 2303H or 2303HX (pin compatible to the older). It’s a chip on board blob, so I, like you, can’t tell for sure what it is. As far as the TTL serial being inverted, I haven’t had any trouble using the cables with Arduino softare and Volksduinos. Have you had trouble with a cable build?

    -r. miloh

  • Marius Kintel

    Regarding inverted TTL serial: As far as I can tell, the UART in AVR’s doesn’t support inverted serial signals. Of course, one could get around this by using bitbanged software serial, but then it’s getting a bit far from having an affordable FTDI cable replacement (which is my goal as well).

    Of course, this extends a bit beyond Arduinos as most WRT devices or other embedded computers also use TTL serial ports.

    If you link to a specific item in such a HK shop, I’ll buy the same cable and do some further tests on my side.

    FYI, this is the one I bought:

    ..might be the same as this one:

  • miloh

    Do your PDA-GPS cables report as PL2303? Interesting. Do you have any photos of the USB/pcb mounting board? If we want to get a more specific chip ID theres some EEprom on the Pl2303 to read. I’m not there yet, but could try that with some encouragement.


    DKU-5 on Ebay…

    There’s more information about modifying DKU-5’s and a good set of links at the end of this post:

  • Marius Kintel

    Thanks for the pointer – somehow the Austrian eBay shop filters searches in a weird way. Using the US shop and subsequently changing country to Austria yielded better results.. I’ve ordered a DKU-5 cable, as well as a CA-42 one – now I just have to sit here for an eternity and a half waiting for the goods to make its way across the globe. I’ll keep you posted.

    Anyway, looking at the link you posted, it appears to me that the DKU-5 cable contains a second chip in addition to the PL2303. Although it has no markings, I’d expect this to be an inverter, perhaps combined with a level shifter, perhaps to 3.3V if the PL2303 in question is the 5V version.
    Doing an oscilloscope test on the TX pin of the 2303 and the TX you give to the Volksduino should set this straight though.

    This discussion feels like it should be wikified btw…
    I’ll make some pics of my existing cable as well – tomorrow…

  • r. miloh

    Some extra points to mention: I got 30 DKU-5’s to work with at about $2.00 each, since learning more about them I think $1.00 is the most I would pay for them in volume, preferably less. The shipment included 2 types of DKU-5’s that I will document on the Noisebridge wiki. It doesn’t look like there are any inverters on the pcb’s.

    For now, zoom in on the photo in the blog post, there’s a spare pcb/usb DKU-5 that’s lying on the table. This pcb has markings for an missing 8 pin IC, making the blob chip the only chip used…

    -r. miloh

  • Marius Kintel

    Hi again,

    Some more info about my device:

    Descriptor Version Number: 0x0110
    Device Class: 0 (Composite)
    Device Subclass: 0
    Device Protocol: 0
    Device MaxPacketSize: 64
    Device VendorID/ProductID: 0x067B/0x2303 (Prolific Technology, Inc.)
    Device Version Number: 0x0300
    Number of Configurations: 1
    Manufacturer String: 1 “Prolific Technology Inc.”
    Product String: 2 “USB 2.0 To COM Device”
    Serial Number String: 0 (none)


  • blackthursday

    hey miloh,

    this is jason from oklahoma :) i just wanted to let you know that the cable you made me is working great. also, i found that you can easily make it look finished by adding a little sugru to the exposed wires.

    thanks for all the help earlier this month!

    we hope to have our space, OHM (, up and running soon!

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