USB port identification

[andrewlapham]

Hey, i picked up this GPS receiver from the second-hand store today and realized the USB cable wasn't included. i wanted to replace the female port with a standard mini USB port but quickly ran into a problem. the USB port in the device only has 3 wires attached to it and after inspection, i found some pads under a sticker that looks like a USB header but it still doesn't look right as it has 6 pads.  any ideas about what I'm dealing with here?

[ejeffrey]

Usb <= 2.0 only has 4 pins.  5v, 0v, d+, d-. A usb target (not host) that is self powered only really needs to use the three pins.

[viperidae]

That rdc r1120 MCU doesn't appear to have a USB peripheral. The proprietary USB cable may be a USB to UART adopter.

Edit: the sp385 is an rs232 level translator
The other 2 visible chips are the GPS chip and an SRAM. I don't see anything on that PCB with a USB controller.

[andrewlapham]

so I'm guessing this needs an additional TTL Serial to USB bridge?

[MarkMLl]

It looks to me as though five pins have traces or nearby vias on that connector, including gnd and 5V in the middle which is rather unlike USB. I've seen something (although I forget what) recently which used a USB connector for low-voltage serial, and this might be doing the same.

MarkMLl

[andrewlapham]

So i just found the for the manual for the device and it originally had a 1394 (firewire) to PS/II --PS/II to USB. (the PS/ii to USB is what I'm missing)

[angrybird]

The 5 pin connector that is unsoldered(unpopulated) looks like a standard USB connector to me.  The 5th pin is the ID pin - Relevant specs: USB 2.0, USB OTG, USB BC1.2

If this device is self powered, it's unlikely that it uses the ID pin, however I do see a trace running to it so maybe there are multiple flavors of this device.

[angrybird]

Also it's relevant to mention that while only 3 pins may be required for communication w/o power, a peripheral still needs the power pin to allow for attach detection.  There are some other methods like DCD (Data Contact Detect) but they are not terribly reliable.  The attach->connect event is started by the peripheral seeing the 5V input rise >= 4.01V, without this pin it can't detect this.  I suppose it could blindly leave its pull-up (Rpu) enabled all the time, or wait to see the termination resistors on the host side, but this would violate USB specs and it wouldn't pass compliance testing.

[MarkMLl]

@angrybird: OP's already determined that it's not USB:

> So i just found the for the manual for the device and it originally had a 1394 (firewire) to PS/II --PS/II to USB. (the PS/ii to USB is what I'm missing)

MarkMLl

[angrybird]

I should have specified "in the picture" -> There are PCB lands for an unpopulated 5-pin USB connector on the PCB shown in the picture.

[MarkMLl]

If that were USB one of the middle traces would not be prominently labelled "5.0V".

MarkMLl

[angrybird]

Oh!  That's a SIX pin connector!  DOH!  I swear I saw five!!!   

[MarkMLl]

[Nod] with vias on the outer pins, so they're probably not shield. Some one-of-a-kind internal connector, with what OP describes as a "PS/II" involved.

"Connector golf" can be a fun occupation, until one is doing a field job and finds that the schematics available aren't remotely like the hardware :-)

MarkMLl

[angrybird]

At least the pin density on this one is reasonable!  I've been handed the task of tacking very fine mag wires (~36AWG if I remember correctly) onto one of the inner layers of the multi layer ribbon cable going to an Apple device screen...  Honestly, I don't know what was more difficult, soldering them on in the first place, or working out strain relief so that they wouldn't break off during testing...

[andrewlapham]

Ok, guys. I'm still stuck trying to interface with this device. I'm going to need USB as an interface medium for use with my laptop but as i stated before i am missing the 1394(firewire) to the USB connector. I've included a picture from the manual to show all the different interface mediums available to the device such as RS-232 serial, CF-PCMCIA compact flash, and USB.

I was thinking of pushing the serial DB9 connecter through a TTL serial converter to use it as a USB interface but I'm not sure how to power the device if i do it this way or if it's even possible.

DB9                     USB TTL
Pin 2 (RX)      --    TX
Pin 3 (TX)      --    RX
Pin 5 (GND)   --    GND
               --    VCC (3.3 or 5)

I've included some images of the hardware I'm planning on using.

[MarkMLl]

So "PS/II" comes into it purely because they've used a PS/2-compatible cable as an extension, with a mini-DIN at each end. You might be able to hack it using something like an FTDI adapter, I suspect that "1394(firewire)" might indicate simply the outline of connector they'd used rather than suggesting signalling levels and protocol.

It's the middle cable of the ones shown in your photo that gives the useful info: it looks as though it's intended to plug into a PC's keyboard or mouse connector to get power and then puts some unspecified signalling level onto the 9-pin D connector... you could usefully check what that level is.

I'd be inclined to try an FTDI but to be prepared for something to blow up, but allowing for the commodity nature of GPS receivers and FTDI adapters these days it's not worth putting a great deal of effort into.

MarkMLl

[pcmad]

that port looks like the connector from older cameras that had the feature of svideo combied with that connector

[angrybird]

This picture is very helpful!  I suspect you will find an RS232 level serial interface and nothing more!  The adapter pic you posted looks like a TTL level converter, you might want to also get an RS232 level converter, I kind of suspect this is what you will find based on the pics (The PS/II to DB9 connector hints towards this)