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How to Make a 9-Pin Serial to Ethernet Cable

Picture of How to Make a 9-Pin Serial to Ethernet Cable
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These instructions will show you how to make a 9-pin serial to Ethernet cable. Serial cables are used to control and configure devices with serial ports. When converting one end to Ethernet, the signal is able to travel farther. When devices are spread out over a large area or placed inconveniently, such as ceiling-mounted projectors, being able to control multiple devices from one spot saves time and money. Only patience is required to make these cables; no prior knowledge necessary. It will take around an hour to complete a cable. After a few practice cables, they can be made in 10 to 15 minutes. With the ability to control devices from a stationary spot, you don't have to worry about searching for a remote or physically pushing buttons on the device.


Required Parts and Tools

Digital Multimeter
Wire Crimpers (Optional)
1 - RJ-45 connector (Optional)
Wire Strippers
Electrical Tape
[1]9-Pin Serial Cable
[1]Ethernet Cable
[2]4-Wire Splice Connectors
 
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Step 1: Strip the Serial Cable

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1) Cut the serial cable using the wire strippers, leaving a couple feet on the female end.

2) Using the strippers, remove roughly 2 inches of the cable covering on the cut end to expose the inner wires.

Step 2: Map the 9 Pin Holes to Inner Cables Using Multimeter

Picture of Map the 9 Pin Holes to Inner Cables Using Multimeter
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1) Set multimeter to smallest Ohms setting (symbol looks like horseshoe).

2) Insert either multimeter rod (red or black) into first pin hole of serial cable.

3) Make contact with inner wires (inside inner shield) with other rod one at a time.

4) When the multimeter picks up a reading, then the pin hole being used is connected to the wire being touched.

5) Repeat steps 2-4 until all inner wires are mapped to their pin holes.

Step 3: Remove Unnecessary Inner Wires

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1) Look in the device manual or online to find which pins are designated for the following:
a) Transmit
b) Receive
c) Ground (there may be multiple, pick only one)

2) Set aside the inner wires corresponding to the designated pins along with the bare wire (also ground).

3) Cut off the unnecessary inner wires.

Step 4: Strip the Ethernet cable

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1) Cut the Ethernet cable using the wire strippers, leaving the desired length to work with.

2) Remove roughly 2 inches of the cable covering on the cut end using the wire strippers to expose the inner wires (there should be 4 twisted pairs).

Step 5: Determine Designated Inner Wires for Ethernet Cable

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1) Place the tab on the end of the Ethernet cable face down with the golden pins face up.

2) Determine which inner wires are connected to pins 3, 6, 7 and 8 counting from left to right (usually green and brown pair).

3) (Optional) Use RJ-45 end and wire crimpers to recrimp the Ethernet cable if it's not standardized.

Step 6: Remove Unnecessary Inner Wires from Ethernet

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1) Set aside the 4 inner wires connected to the designated pins (2 twisted pairs).

2) Cut off the other wires, along with the inner plastic piece, if there is one (on most new cables).

3) Untwist both pairs.

Step 7: Connect Inner Wires of Serial and Ethernet

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1) Push the inner wires corresponding to pins 3 and 6 of the Ethernet cable into the same side of 1 of the 4-wire splice connectors.

Caution: Make sure to push wires as far back as they will go into the 4-pin wire splicers to ensure a proper signal flow and avoid malfunctioning cables.

2) Clamp down the used side of the 4-wire splice connector using the end of the wire strippers.

3) Repeat steps 1 and 2 for the inner wires corresponding to pins 7 and 8 of the Ethernet cable using the other 4-wire splice connectors.

4) Push the inner wire of the serial cable corresponding to the receive pin into the opposing slot of the 4-pin wire splicer containing the inner wire corresponding to pin 3 of the Ethernet cable.

5) Repeat step 4 for the remaining inner wires corresponding to the following pins:
a) Transmit pin of serial cable to pin 6 of Ethernet cable (clamp down completed side).
b) Ground pin of serial cable to pin 7 or Ethernet cable.
c) Bare inner wires of serial cable to pin 8 of Ethernet cable (clamp down completed side).

Step 8: Cover Connections Using Electrical Tape and Clean Up

Picture of Cover Connections Using Electrical Tape and Clean Up
1) Wrap electrical tape from the cut of the serial cable to the cut of the Ethernet cable, covering the 4-wire splice connectors, to secure and protect the connections. Usually you should try to match the color of the cables for best appearance. I only had red tape!

2) Clean up the mess and put away the tools; it's time to test the new cable.


Congratulations! You now have a (hopefully working) 9-pin serial to Ethernet cable. If there is a problem, it usually has something to do with mapping designated pins with correct inner cables. First, try to re-crimp the 4-wire splice connectors to ensure a solid connection. Then go back and check your cable mappings. Think of all the other cables you can cross with an Ethernet cable!
orator2 days ago

Why not just install a RJ-45 connector on the wires of the D-9 cable?

bradw6 days ago

The title is somewhat misleading. This isn't a serial to Ethernet cable; it's a 9-pin D shell to RJ45 cable with no serial to Ethernet protocol conversion. Which is still useful of course, since some devices (switches/routers is what I've seen) have serial ports with an RJ45 connector.