S/PDIF optical

From HwB

Optical S/PDIF circuits

Very cheap optical S/PDIF output

With TOSLINK modules available for as low as $10 it hardly seems worth it to bother with the trouble of making your own TOSLINK module due to the fact that the ones from Sharp have a built-in connector and are much easier to interface. But if you really want to make your own optical output interface, you can do it because S/PDIF optical (TOSLINK) transmitter is just basically a red LED coupled to the optical fiber. So to build a very basic output circuit you only need a red LED and a resistor, both available from any place where electronic components are sold.

The circuit is very simple:

                   _____
TTL signal -------|_____|---------
                                  |
                                 ---
                                  V  LED
                                 ---
                                  |
    Ground -----------------------

The idea of the circuit is that the digital data is fed through a series current limiting resistor to the LED (typically LEDs only require 5-30mA). A digital 0 is 0V and the LED is off. A digital 1 is 5V and the LED is on. That's it!

If for some reason the circuit does not work, try to change the LED and also try to connecting it better to the optical fiber. NOTE: Not all LEDs will work, so you may have to experiment a bit. Optimally, you want a high-brightness RED LED with a typical wavelength of 660nm.

If swapping the LED doesn't work, you might want to try using a hex inverter (7404 or similar IC) to buffer the signal. This might be good practice too, just in case the TTL SPDIF output of your source device isn't designed to handle a 20~30mA load this circuit generates.

Commercial modules

Contributors

Joakim Ögren

Sources

ePanorama.net: S/PDIF by Tomi Engdahl