Senior Design II paper
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- Sony/Philips Digital Interconnect Format (S/PDIF)
- Analog to Digital (A/D) Conversion
- Stellaris ARM Cortex LM3S1110
- Atmel Atmega328
- Not using Analog to Digital (A/D) Conversion
- Connecting the headphones to the television PCB
- Connection between the A/D boards to the Master Controller
Television Audio Adaptor
There are several different approached to transmit the audio from the televisions to the headphones. The audio would have to be routed from the televisions and into a microcontroller. The microcontroller would then transmit the data to a master microcontroller. The methods to transfer the sound to the microcontroller are Sony/Philips Digital Interconnect Format (S/PDIF), HDMI, and RCA.
S/PDIF is a special digital audio connection for most receivers, TVs, stereos, and movie devices.[11] It was invented by Sony and Philips to create a high definition sound that would replace analog sound connectors. The cable used for this connection was either a fiber optic cable or a coaxial cable. For the project, this presented a problem. Older televisions do not have digital audio connections. It is not financially sound to go buy newer televisions when the project already has older ones donated to the project.
High-Definition Multimedia Interface (HDMI) is a newer technology that eliminates many other cables as well as providing a clearer sound and video than older technologies.[12] However, this technology is not cost efficient for the project or compatible with the donated televisions. The cables alone are over $20. There are other complications with the technology as well. With HDMI, the video is included with the audio. Since the headphones receive only audio, separating the audio from the video stream will increase the workload of the team.
Radio Corporation of America introduced RCA in the 1940’s for radio phonograph consoles. The concept is still the same; however the technology has advanced somewhat since then. RCA adapters have been in home audio/video equipment since the 50’s. In fact, almost all televisions today still have RCA adapters. This is a large reason for the selection of using RCA connectors in the project. The televisions that have been donated to the project are older and do not have HDMI or digital audio. RCA cables and adapters are certainly much cheaper than HDMI. The analog output from the televisions is all that is needed to transfer the sound to the headphones.
The main function of the television PCB will be to convert the data coming from the television into digital data. Since the team is going with RCA (an analog audio output), the information must be converted into digital in order to transmit it to the master microcontroller. On Digikey.com the parts range from $3.83-$9.42. Luckily, all of the microcontrollers can be sampled and cost will not be an issue.
As shown in the Table 3, the MSP430 has 8 pins that are devoted to converting analog to digital [13]. After the microcontroller converts it to digital audio, the microcontroller will then prepare it for serial transmission to the master microcontroller. Luckily, the headphones will convert the sound back to analog for the user to hear the televisions.
Table : MSP430 A/D Pins
Another Microprocessor available to for this project is the Stellaris ARM Cortex. The advantage of the Stellaris is the 32-bit ARM Cortex M3 Processor Core.[14] The Stellaris provides more processing power than the ATmega or the MSP 430. As shown in Table 4, the Stellaris has two Analog Comparators. The Analog Comparators will take in the two analog RCA inputs and output a discrete signal. The discrete signal will then be transmitted by serial to the master microcontroller.
Table : Stellaris A/D Comparators
The Atmega328 is an 8-bit microcontroller that would work efficiently in the system without converting the analog data to digital data [15]. Although the Atmega328 has analog inputs (listed in Table 5), it does not have the processing capabilities that the master microcontroller would need. The cost, however, is quite low. At $3.83 on digikey.com, the price is phenomenal.
Table : Atmel A/D Pins
There is an available option to not convert the analog sound into digital sound. This process can save up to $50 in costs. It would allow the team not to buy microcontrollers, many different circuit elements, and many different connectors. Without the microcontroller to handle the sound, the only component that would be on the televisions is the IR receptors. The sound would travel from the televisions and be processed by the master controller.
Another option available to the team is to connect the headphones into the A/D circuit. With most retail RF headphones, there is a home base that connects directly into the television. However, the team needs to connect it to a microcontroller to have the GUI switch the television’s sound to the right headphone. A possibility is to attach the base to the same PCB that will be converting the television’s audio. Since the connector only uses one of the microprocessor’s pins [16], there will be enough pins to connect the headphone jacks to the board. After, the GUI will switch sound to whichever television a particular headphone is looking at. The command is then rerouted to the particular board with the specific headphones. The disadvantage with this system is how confined it is to the MSP430. The Stellaris and the Atmel only have two A/D convertor pins.
With the use of either Bluetooth or RF, the sound data can be transmitted wirelessly. After the sound is converted to digital by 3.2.2, the data would then be transmitted to the master board. After the transfer, the data would then be processed by the master board and would switch the sound to the correct headphone. The issue with the wireless connection is the possibility of interference. As well as the A/D to master transmission, the triangulation and the headphones will also transmit wirelessly. If there was not as much wireless technology being used, the wireless connection could be used in this project.
The other possible way to connect the A/D boards and the master board is through a wired connection. After the conversion from analog to digital, the data would pass through a serial connection and be transferred to the master microcontroller. This method will eliminate outside interference. This process is also more cost efficient. Cutting down on circuit components, such as wireless chips or modules, will decrease the cost of the device immensely.
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