How to make a dual USB and serial cable from the Nikon Coolpix E990 USB cable.

Use this information at your own risk...
The Nikon Coolpix E990 camera has a built-in communications port that supports both USB and regular serial (RS-232C) connections but the camera is supplied with only a USB cable. The serial cable is, in most parts of the world, an expensive special order item. I decided to have a look at building my own serial cable. The connector on the camera end of the USB cable appears to be a custom part so making an entirely separate serial cable was out of the question. However, the connector does have all 8 pins installed while a USB cable like this needs only 4. The USB cable itself is made by LTK and has the following information silk-screened onto the insulation:


implying that this is a 4-wire cable with 1 twisted pair and two other conductors. Thus the remaining 4 pins are free and indeed represent the connections for a serial cable. This web page documents the project of converting the supplied USB cable into a dual-purpose USB/serial cable. IMPORTANT NOTE: This project requires work on a very dense connector with 28 gauge wire (very fine) as well as soldering in very close quarters. Be certain that this project is within your abilities before cutting up your cable; Take a close look at the pictures and compare them to your UC-E1 cable to get a sense of how small this connector is!

One of the reasons for attempting this modification in the first place, is that a number of nice software tools have been or are being written to access and control the Coolpix cameras via both the USB and the serial port. This software and other work going on around the net includes, of course, Eugene G. Crosser's original photopc and his protocol description Bruce Lightner is the provider of the official Windows 9x/NT and MSDOS versions of photopc. Bruce is also one of the creators of the PicoWeb embedded web server, a very neat product. John Bowman at the University of Alberta's Department of Mathematical Sciences, has updated both photopc and the protocol document with the USB photopc for the 950/990.
The group is also hard at work and gPhoto2 has been released and supports a wide range of cameras. There are also a number of frontends available for it.

Per Madsen is working on some programs (Windows only / no source is available) for controlling the E990 via the serial cable and also posted a nice diagram of the serial connector wiring. Per plans to charge for his software and it currently requires you to register or wait for a timeout when loading and for each snapshot. Also the downloads are rather slow but this is being worked on. Charlie Wallace also has a program, cPix , (Windows only / no source is available) which uses the USB connection instead. In fact my camera and laptop don't like NikonView via USB at all but work just fine with the USB photopc and cPix.
Another contributor to the Nikon Talk Forum on,  Didier, posted a good photograph with the pinout with labels for the camera-end of the both cables (this picture had one small error in that there is no connection between the GND and shield for the USB side.) Following our discussions, Didier has also now produced with a dual-purpose cable of his own, which you can view along with an earlier copy of my "Drawing 1" at his web site. His site also has some good pictures of the steps he followed in making his cable.
The current versions of my diagrams, Drawings 1 and 2, can be found here, near the bottom of this page.

The first order of business is to open the camera-end of the Nikon-supplied camera-to-USB cable. The outer plastic shell (cover) of the connector is separate from the inner connector and wire so it is possible to cut open the cover by carefully slicing along one side. (see the picture at the top of this page)
Once the slice is complete, the outer plastic cover can be removed revealing what appears to be injected plastic covering the wires and the solder tags of the connector. This inner plastic layer has to be carefully removed.

Whatever tool you use to remove the plastic, be patient and make sure the tool's cutting edge is very sharp.

By slowing working on this injected plastic with an X-acto knife and some angle cutters I was eventually able to free the actual connector assembly inside. I also unsoldered the wires once I had removed enough material to gain access to the solder points. Doing this allows you to more easily peel off the remaining injected plastic without having to worry about damaging the solder tags or the wiring. If you are going to make a single "Y" cable by adding wire to the existing configuration then you may want to leave the existing USB wires soldered to the connector, but you will need to be certain that none of the wiring has been damaged during the plastic removal.
However, the plan here is to make a multi-segment cable so all the wires need to be removed from the camera-side connector. As the pictures show, the connector has 8 solder tags, 4 each for the USB and the serial (what appears to be RS-232C) communications links.

Once all the extra plastic is removed and the wires unsoldered, the rebuilding can begin. It is important to note here that the serial communication link includes a short (electrical connection) between 2 of the pins on the camera's communication connector. This is how the camera seems to identify the serial cable connection. In making a dual-purpose cable, there is the need to ensure that only one type of communication connection is made at a time. This is the primary reason I decided to make a multi-segment cable instead of a one-piece cable with a switch. I chose miniature DIN-8 connectors for joining the segment halves together.
There are two diagrams at the bottom of this page which include all the circuit information and drawings needed to make a multi-segment cable. The following items are needed to make this dual-purpose cable:
  • the camera connector just removed
  • the remainder of the Nikon USB cable
  • one (1) mini DIN 8 receptacle
     (female/with sockets)
  • two (2) mini DIN 8 plugs
     (male/with pins)
  • a length of shielded cable with at
     least 8 conductors
  • one (1) DB-9 receptacle
     (female/with sockets)
  • wire strippers, soldering iron etc.
The mini DIN 8 connectors are available from a number of sources. I purchased very basic models from a local company and Digi-Key carries similar if not identical products from companies like CUI Stack.

Miniature DIN-8 Part numbers
 CUI Stack

The image on the left shows an example similar to the CUI Stack MD-80J part, the miniature DIN-8 in-line receptacle kit. The mating part, similar to the MD-80 plug, is shown in the picture below, on the right, already connected to the serial cable segment.
Drawing 1 (see also below) shows the solder tags for the pins of the camera connector, the circuit information for the existing Nikon USB and Serial cables and a table mapping pin numbers to communications functions. Note that my numbering of the camera connector's 8 pins is entirely arbitrary and is provided only as a build reference. Drawing 2 (see also below) represents the circuit diagrams for the each of the 3 new cable segments. As shown in the picture above, on the right, the new communications cable assembly includes a camera segment, a serial segment and a USB segment.
The serial segment includes a connection between pins 2 and 5 of the camera connector; this connection forms a circuit that tells the camera that it has a serial cable connected to its communications port. This is also why the USB and serial communications links must be used separately. For completeness I should mention that the wiring includes shielding which is connected to the metal connector shields at each end of the USB and the serial cables. The actual USB wire includes a foil, a braid and a ground wire. The ground wire is attached to the ground tab on the connector; the braid and foil are cut back. The wire I used for the camera and serial segments included the foil and ground wire but no braid.

As shown in Drawing 2, the camera segment has the Nikon camera connector on one end and the mini DIN 8 receptacle (female/with sockets) on the other; the serial segment has a mini DIN 8 plug (male/with pins) on one end and a DB-9 receptacle on the other; the USB segment has a mini DIN 8 plug on one end and the Nikon cable's USB connector on the other.
In order to make the wiring easy to follow I chose to wire the camera segment DIN 8 receptacle following my arbitrary pin numbers on the camera connector (shown in Drawing 1). Thus pin 1 on the camera connector is wired to pin 1 on the DIN-8 receptacle; pin 2 to pin 2 etc. The camera segment has all 8 wires (plus the shield/ground) while the serial segment uses pins 2,3,4 and 5 and the USB segment uses pins 1,6,7 and 8 on the DIN 8 plugs. NOTE that the diagrams show the connectors as they would appear from the mating or outer ends, not the wiring side. Also the receptacle and plug connectors will appear as mirror images of each other (reversed.)
I would be interested in any comments about the layout I used for these diagrams as well as any of the information provided; suggestions for making any of it more clear and easier to follow are welcome.

I have now done some initial testing with this new cable setup. Using a laptop I was able to get ~84kbps(kilo bits per second) with the serial cable setup and ~2Mbps with the USB cable setup. NikonView 3.0 and 3.11 were both used for the serial tests and photopc and cPix were both used for the USB tests. For some reason neither version of NikonView works for me with the USB connection.

I would prefer to find some better wire to use, particularly for the camera segment and I will need to look at a more permanent method to reclosing the camera connector shell once I'm satisfied with the cable assembly.

More news will follow...  


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