Tech-tips : DB-9 Connectors

Continuing our series of useful best practice articles in co-operation with InfoComm International, this month we focus on the correct termination of the DB-9 connector. Whilst IP-based control may eventually supersede it, the humble serial connection is here to stay for the foreseeable future.

The DB9-type connector is commonly used in the AV industry for terminating shielded twisted pair cables for serial control connections such as RS-232 and RS-485. It has 9 pins, but you should follow carefully the manufacturer’s instructions for any devices you are connecting as you may not have to always terminate all of them. In a DB-9 RS-232c serial connection, pins 2 and 3 are used to transmit and receive data to/from another device, while pin 5 is the ground reference. Equipment will vary as to which signal is present at which pin/socket. The critical thing to remember is that the Tx signal on equipment A will need to be connected to the Rx signal on equipment B. (See fig. 1)
Additionally, some connectors may come packaged with their pins separate and needing to be inserted into the connector shell. It is best to install unused pins to assist in lining up the connectors during mating.

A. Verify that you have all the connector components you need before you begin. (See fig. 2) Then slide any heat shrink tubing over the cable that you intend to use as strain relief

B. Trim the outer jacket so the individual wires can fit within the connection area without sharp bends. The outer jacket must fit within the strain relief after the job is completed. Trim the inner conductors so that they are easily placed into the solder cups. The insulation should be held back from edge of the solder cup a distance no greater than the diameter of the wire.

NOTE: The DB-9 connector can become quite crowded. It is a good idea to include some form of insulation between connection points after the soldering has been completed. Slide some heat sink tubing over the individual wires or at least every other one.

C. Most technicians prefer to start soldering with the inner pins and work outwards. After soldering is complete, use a multimeter to test for shorts between pins. (See fig. 3)

D. Slide the heat shrink tubing over the solder cups, and heat with a heat gun. Install the strain relief onto the cable jacket and assemble the hood components to complete the connector. (See fig. 4)

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