How to build an optical SPDIF bracket

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WARNING:

Creating, testing and using home built electrical circuits and connecting these to your computer's motherboard may pose the following risks: - electrical fire - toxious fume inhalation - burning of skin or face by using a soldering iron - damaging perfectly working parts of youyr motherboard or audio equipment ..however that being said, this procedure should be feasible with average technical skills and little tools and equipment

Introduction

Most MythTV systems these days are built using a motherboard with integrated audio and video. However, the SPDIF signal is unfit to be wired directly to a SPDIF compatible digital audio receiver. The reason is that the signal is a TTL signal, while it should be a signal swinging between -0.5V and +0.5V. This requires that a simple circuit be built, using some resistors and a capacitor, but the signal can not be used to drive a long cable and thus additional components like a 74HCT04 are needed to amplify this signal to acceptable levels.

This article describes how you can build a SPDIF TOSlink transmitter circuit, using just two components.

Advantages - Optical link means no GND loops, total isolation can be achieved with your receiver (however, your DVI cable will contain a GND connection to your TV, and if these share connections, there will be at least a common GND signal anyway) - no electrical interference possible - cheap, simple Disadvantages - optical TOSlink cable needed - receiver needs to have a optical TOSlink input (most modern ones have that)

Requirements - Motherboard must have a SPDIF header - SPDIF should be unmuted (see other articles about the software setup)

Hardware needed - 1 SPDIF optical transmitter unit, this article describes the Toshiba TOTX173 - 1 8.2K ohm resistor, 1/4 watt 20% tolerance - 4 pin header, commonly supplied with the motherboard for interconnection of SPDIF to DVI - heat shrink isolating sleeve 3mm diameter - thin solid core copper wire - soldering iron - soldering tin for use in electronic (resin core, not acid core)

Literature needed: - Application sheet from Toshiba for the TOTX173, download it here - manual for your motherboard showing the pin layout for the SPDIF. This one is important, don't guess which pin is which, it may damage your motherboard)

Procedure: -

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