DIY Datalink Adapter

Arduino Uno based Notebook Adapter compatible with original Timex Datalink software that eliminates the requirement of syncing with a CRT monitor


  • Arduino Uno
  • Arduino software to upload to an Arduino Uno
  • Software libraries for Arduino (see below)
  • RS232 TTL hat (I used Anmbest MAX3232 3.3V to 5V DB9 Male RS232 on Amazon)
  • Red LED (with 1k resistor on GND between LED’s ground wire)
  • 4 short wires with Dupont connectors that are male on one end, female on the other
  • Null modem cable to connect TTL adapter to PC
  • Windows 9x PC or virtual machine with serial port and Timex Datalink software installed (verified with 2.1d)
  • Timex Datalink watch (tested with Datalink 150)

Libraries Used

This currently requires two Arduino libraries, add them with the Library Manager in the Arduino software.

  • AltSoftSerial (tested with version 1.4.0)
  • DigitalIO (tested with version 1.0.0)

Connecting it all

Connect the Arduino Uno to RS232 TTL adapter using wires with Dupont connectors. Add an LED with 1k resistor. Power the Arduino Uno via USB. Connect null modem cable from the PC to the TTL adapter.

  • Connect pin 9 on the Arduino Uno to TX on the TTL adapter
  • Connect pin 8 on the Arduino Uno to RX on the TTL adapter
  • Connect 5V on the Arduino Uno to VCC on the TTL adapter
  • Connect any GND on the Arduino Uno to GND on the TTL adapter
  • Connect pin 12 on the Arduino Uno to the postive/longer leg on the red LED
  • Connect any GND on the Arduino Uno to a 1k resistor and other end of resistor to the negative/short end on the red LED
  • Connect USB type B to power source (does not currently use USB for data/communication)
  • Connect null modem cable between TTL adapter and PC

How to use

Right now you need to reset the board after each usage (including watch test). Just use the reset button on the board, no need to unplug the power. Otherwise, use as you would the official Datalink Notebook Adapter, following in-app directions.

Special Thanks


Timex, Datalink, and DATA LINK are the registered trademarks of Timex Corporation. This project is not associated with or sponsored by Timex.


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