Clock & Timer Circuit DiagramsSignal Generators

Optical S/PDIF Output Schematic Circuit Diagram

Expanding Digital Output Access

The purpose of this compact circuit is to extend the functionality of a computer’s CD or DVD drive by offering external access to an unused digital output. Notably, it creates an electrically isolated interface for improved connectivity. Moreover, this circuit proves to be quite practical for linking a portable MiniDisc (MD) recorder, as these devices typically feature solely optical digital inputs.

Optical S PDIF Output Schematic Circuit Diagram

Optical S PDIF Output Schematic

Enhanced Toslink Transmitter Module Circuit

This circuit represents a conventional application of the Toshiba Toslink transmitter module. Due to the substantial interference prevalent in the PC environment. Additional decoupling for the transmitter module is incorporated through L1, C1, and C2. A small PC power connector can be affixed to the pin header K1 (attention to orientation is crucial; +5 V corresponds to red). The cable from the S/PDIF output of the CD or DVD player can be linked to K2. Ensuring accurate connection of the signal and ground leads is vital. Typically, players equipped with an S/PDIF output come with a suitable screened cable. Alternatively, one can craft a custom single-lead screened cable featuring a two-pole connector for a pin header at each end.

Optical S PDIF Output Schematic Circuit Diagram 2

Direct Connection to Toslink Transmitter

In most cases, drives offer a standard logic level at the digital audio output, allowing direct connection to the Toslink transmitter input without any necessary modifications. The circuit consumes approximately 13 mA. However, it is worth noting that specific CD and DVD drives emit a signal from the S/PDIF output only during CD playback. In the absence of a disc, there is no S/PDIF clock signal present.

This behavior leads to a minor issue for recorders, as they may miss a small portion of the signal when an audio CD begins playing. This occurs because the PLL of the clock extraction circuit must re-lock to the clock signal after the playback starts. Unfortunately, the PCB illustrated here is not readily available pre-assembled through the Publishers’ Readers Services.


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