How to make Dell CT109 serial to PS2 cable – Learn how to build a custom Dell CT109 “Serial to PS/2” cable in this step-by-step guide. Discover pin layouts, tools needed, and pro tips for a hassle-free DIY.

If you’re working with older Dell computers or legacy peripherals, you might run into the Dell CT109 port—a compact, proprietary connector that often doubles as a “serial-looking” interface to support PS/2 mice or keyboards. Although it looks like a standard serial (DB9) port, the CT109 can carry PS/2 signals through a custom pin layout.

In this DIY guide, we’ll walk through the process of creating your own Dell CT109 “serial to PS/2” cable. We’ll cover what tools you’ll need, the general wiring principles, and essential tips to make sure your cable works smoothly. Please note that wiring can vary depending on the exact Dell model, so always check your motherboard or device-specific documentation when possible.

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Why the Dell CT109 Connector Exists

Back in the late 1990s and early 2000s, certain Dell laptops and desktops minimized their port real estate by using proprietary connectors. Instead of giving you separate PS/2 mouse and keyboard ports, Dell sometimes combined those signals into one small port (the CT109). By default, you would need a Dell OEM “Y-cable” or serial port to PS2 adapter out of this single plug. Nowadays, finding ps/2 to serial adapter can be challenging or expensive on the secondhand market, so building your own cable is a budget-friendly solution—especially if you’re comfortable with soldering and following pinouts.

Disclaimer and Safety First

1. Voltage and ESD Precautions: PS/2 lines carry +5V power. Always power down your PC and unplug it from the wall before you start wiring or plugging things in.
2. Tool Safety: Use a well-ventilated area for soldering and wear appropriate safety gear (goggles, gloves).
3. Check Device Documentation: Different Dell systems can have slight variances in pin layout. Confirm your specific computer’s manual or motherboard reference if you can.
4. Proceed at Your Own Risk: Incorrect wiring can damage your devices. If you’re unsure, consult a professional or search for an official Dell adapter.

Tools & Materials You’ll Need

1. Dell CT109 Connector: You’ll either need to salvage one from an old cable/adapter or purchase a compatible 9-pin connector that fits the Dell port (not all 9-pin connectors will physically match the proprietary shape, so be sure it’s specifically CT109-compatible).
2. PS/2 Connector (Mini-DIN 6): For the mouse or keyboard plug end. You can also get a “Y-split” PS/2 connector if you want two ports (one for mouse, one for keyboard).
3. Wire and Heat Shrink Tubing: Gauge-wise, 26–28 AWG is usually sufficient for low-power PS/2 signals.
4. Soldering Iron & Solder: For solid, durable connections.
5. Multimeter: For checking continuity and ensuring correct pin-to-wire mapping.

Understanding the Pin Layout

The critical part of building your own Dell CT109 to PS/2 cable is matching the correct pins on the CT109 connector to the correct pins on the PS/2 connector(s).

Here is a general reference for many Dell CT109 ports (note that “Serial to PS/2” here is actually a proprietary arrangement where the signals are PS/2-level, not RS-232 voltage levels):

Note: The actual pinouts may differ depending on your device. Some CT109 cables are purely for a single PS/2 mouse, while others split into two PS/2 ports (keyboard + mouse). If you’re making a single-cable solution (one PS/2 device), you will only use the lines for one set of Data/Clock pins, plus +5V and Ground.

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9 Steps to Make Dell CT109 Serial to PS2 Cable

1. Prepare Your Work Area

• Lay out all components: the CT109 connector, the PS/2 connector, your wires, soldering iron, and multimeter.
• Ensure your PC or device is unplugged and powered off.

2. Identify Pins on the CT109 Connector

• Look closely at the CT109 connector to identify each pin by number. Some connectors are labeled; others you may have to consult a diagram or reference photo.
• Use your multimeter in continuity mode to test which physical pin on the connector corresponds to each wire if you have a breakout or pigtail.

3. Identify Pins on the PS/2 Connector

• PS/2 connectors are usually a 6-pin mini-DIN. The pins can be tricky to see, so be sure to have a pin diagram handy.
• If you’re doing a “Y-cable” for both mouse and keyboard, you’ll have two mini-DIN connectors, each labeled or color-coded (green for mouse, purple for keyboard in many standardized sets).

4. Cut, Strip, and Tin Wires

• Carefully trim the wires to your desired length.
• Strip off a small amount (about 3–4 mm) of insulation from each wire end.
• “Tin” each wire by applying a small amount of solder to make final soldering easier and more reliable.

5. Solder the Connections

• Following your pin mapping chart (and any Dell-specific documentation you have), solder each wire from the CT109 side to the corresponding PS/2 pin.
• Double-check each connection before applying heat shrink tubing. A single wrong connection can render your cable useless—or worse, damage the peripheral or port.

6. Use Heat Shrink Tubing

• Slide a small piece of heat shrink tubing over each solder joint to protect and insulate the connection. Use a heat gun or your soldering iron (carefully) to shrink the tubing in place.

7. Check Continuity

• With your multimeter, verify that every pin on the CT109 side properly corresponds to the correct PS/2 pin(s).
• Make sure there are no shorts between power and ground lines.

8. Final Cable Assembly

• Gently reassemble any connector shells and strain relief (if provided).
• Label the finished cable so you (or someone else) know exactly what it is later on.

9. Test the Cable

• Power on your Dell system and connect your PS/2 peripheral to your newly made cable.
• Look for standard PS/2 detection in BIOS or in your operating system. If the mouse/keyboard isn’t detected, power off again and re-check your wiring or consult additional documentation.

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Troubleshooting Tips

1. No Device Detection
   • Make sure you’re using the correct pins for Mouse Data/Clock or Keyboard Data/Clock.
   • Verify your operating system still supports PS/2 hot-swapping. Some older systems require powering down to recognize a newly plugged-in PS/2 device.
2. Device Works Intermittently
   • Check for loose solder joints or frayed wires.
   • Ensure you have a stable +5V supply going to the PS/2 port.
3. Wrong Dell Model
   • Some Dell laptops use a different proprietary pinout or require a special combination of signals. Always verify if your particular system has the exact same CT109 layout.
4. Damaged Connector
   • If your CT109 connector or the laptop port is worn out, you may need to source a new or good-condition used part.

Final Thoughts

Creating a custom Dell CT109 to PS/2 cable can be a lifesaver for retro-computing enthusiasts or technicians maintaining older Dell hardware. While it involves carefully matching pinouts and a bit of soldering finesse, the satisfaction of getting your vintage keyboard or mouse up and running is well worth the effort.

Remember to always double-check pin mappings for your specific Dell model and practice safe handling procedures. If you run into issues or you’re unsure about the wiring, consult official Dell documentation or seek advice on retro-computing forums. With patience and careful craftsmanship, you’ll be able to breathe new life into your trusty Dell system and keep those classic PS/2 peripherals working smoothly!

Keywords: Dell CT109, Dell CT109 cable, DIY Dell adapter, Dell proprietary port, Dell serial to PS/2, PS/2 mouse, PS/2 keyboard, legacy hardware, retro computing, pin mapping, how to make Dell CT109 cable, step-by-step guide

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