1) serve as usual external USB audio card with headphone/line output and audio line input
2) can transmit the digital audio data at relatively long distance (20m -100m)
3) can receive and process the digital audio data send by the similar card and either transfer it through the USB to the PC, or convert it to analog audio signal
As long distance transfer media was chosen the POF.
A short explanation of the POF technology will be presented:
What is POF?
POF stands for plastic optical fiber with the term plastic being used a vulgarization for polymer materials.
The 1mm fiber diameter is about 500 times thicker than a glass optical fiber. 96% of the cores cross section conducts modulated light for data transmission similar to glass optical fiber applications. The maximal transmission distance amounts to about 100m without active repeaters. Polymer fibers are used for high speed data network in homes, commerce and industry as well as in cars and airplanes. POF is often regarded as an optical home network because POF is easy to install. The fiber is thin, can be shortened to the desired length by a sharp knife and requires no connectors on its ends. Anyone can set up a robust, high performance and Ethernet compatible network without any special tools.
The key advantages of POF networks are:
- No electromagnetic radiation
- Electrically isolated network
- Immunity against electromagnetic coupling
- No electromagnetic cross talk
- Flexible, reliable and maintenance-free
- Low weight
- Resistant to humidity, heat and vibration
- Visible light that is eye-safe
Target Markets and Applications
POF is an excellent solution for multimedia and intelligent home networks. In particular, POF is suitable as network backbones to mutually interconnect TV, set top boxes, NetTV, gaming, PCs, network attached servers (NAS), internet and VoIP. Carrier Networks POF is an attractive solution for telecommunication companies, cable networks and infrastructure providers to offer a completely optical solution (Vertical installations GOF (glass optical fiber), Horizontal (floor level) POF). As an electrically non-conducting and against electromagnetic interference immune “cable”, POF is the only cost-effective solution that suits both to old and new buildings.
POF is also a smart alternative to copper cabling in commercial environment. Compared to copper, POF has the following advantages: POF is thin and therefore easy to install and hide. POF is also easily extensible and upgradeable, robust, electrically non-conducting and reliable. Industrial Networks
POF already has a track record for connecting Ethernet-based industrial applications, such as control units within the manufacturing process, industrial control modules and links in the control room. POF is often the only affordable solution to meet the mechanical, electromagnetic and chemical challenge of an industrial environment in a spark-free manner. Car, Aircraft and Train Networks POF does away with the boundaries of today's copper cables in mobile applications by its unique advantages such as like low weight, requires least space, immunity against vibration and humidity.
Further information about the POF and some high speed solution can be found here:
An internet research for audio codec suitable for the realization of the project showed, that the best solution would be the Texas Instruments (Burr-Brown) chip PCM2906.
Here can be seen the chip information: http://www.ti.com/product/pcm2906c
For the POF transmitter/receiver part was used the Firecomms Optolock FC3000T. It includes the transmitting LED and the receiving PIN photodiode in one package. More information about the device can be found under the link: http://www.firecomms.com/ . The used Optolock is analog. Under desire a different type can be used (there are some which contain the receiver part embedded inside the same package), but the schematic and the PCB of the current implementation must be changed according the new requirements (in some cases differential to single ended conversion must be done).
The opamps and the linear regulator used are also products of Texas instruments. (For the audio amplifiers better to use OPA2353UA instead OPA2340UA as given in the Eagle files)
The micro switch comes from http://www.te.com . The electrolyte capacitors are tantalum. The resistors metal film devices.
The Schottky diode requirements are: VF ≤ 350 mV at 10 mA, IR ≤ 2 μA at 4 V. I have used BAT43.
The audio jacks are from the type MJ-352WO (MJ-352). Can be ordered at http://www.farnell.com – article # 1267400.
For the project can be used 12MHz quartz crystal, different from the one I used (NMP120 from Saronix), but the oscillator capacitors must be used according its datasheet.
The project was developed by the use of the CadSoft Freeware software Eagle Light edition.
It can be downloaded here: http://www.cadsoftusa.com/download-eagle/freeware/?language=en
The schematics and the PCB views are presented on the pictures.