The making of an entirely separate serial cable is illustrated in this hacking of a USB cable that came from the Nikon Coolpix E990 camera which has built-in communications port that supports both USB and regular serial RS232C connections. The connector on the camera end of the USB cable appears to be a custom part and contains all 8 pins installed while a USB cable like this needs only 4. The USB cable is a 4-wire cable with 1 twisted pair and two other connections. The connections for a serial cable will be represented by the remaining 4 free pins as shown below.

Opening the camera-end of the Nikon-supplied camera-to-USB cable, just like the image below, is the first order of this hack. It is possible to cut open the cover by carefully slicing along one side since the outer plastic cover shell of the connector is separate from the inner connector and wire as shown in the below image. The outer plastic cover can be removed to reveal what appears to be injected plastic covering the wires and the solder tags of the connector once the slice is complete while carefully removing the inner plastic layer.

The actual connector assembly inside can be freed by slowly working on the injected plastic with an X-acto knife and some angle cutters. To gain access to the solder points, the wires were unsoldered to allow more easily peeling off the remaining injected plastic without damaging the wiring of solder tags. All the wires need to be removed from the camera-side connector in order to make a multi-segment cable. Since the connector has 8 solder tags, 4 will go each for the USB and the serial communications links. The rebuilding can begin once all the extra plastic is removed and the wires unsoldered.

For the camera to identify the serial cable connection, the serial communication link will include a short electrical connection between 2 of the pins on the communication connector of the camera. There is a need to ensure that only one type of communication connection is made at a time in making a dual-purpose cable. The segment halves were joined together using the miniature DIN-8 connectors which are available from a number of sources. The image below shows the camera segment, serial segment, and USB segment.

The miniature DIN-8 in-line receptacle kit is shown in the image below which is similar to the CUI Stack MD-80J part. The next image shows the mating part similar to the MD-80 plug that is already connected to the serial cable segment. A connection between pins 2 and 5 of the camera connector is included in the serial segment. A circuit is formed by this connection which informs the camera that a serial cable is connected to its communications port.

At each end of the USB and the serial cables, the wiring includes shielding which is connected to the metal connector shields. A foil, braid, and ground wire are included in the actual USB wire wherein attached to the ground tab on the connector is the ground wire. the wire used on the camera and serial segment does not contain braid but includes ground wire and the foil.

The first drawing 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. For each of the 3 new cable segments, the second drawing illustrates the circuit diagrams.