Objective – Provide a turnkey product design package
Services – Electrical Design, Firmware Design, & Mechanical Design
Industry – Corporate Communications
Application – Multimedia Switching
Other – Integrated Third-Party Remote Controller

Overview
All Communications (All) sought a device enabling it to add value to the video teleconferencing systems it provides to customers. This device would give All a product with its own private branding to be associated with the sophisticated systems it was integrating. They selected to build an Audio/Video 1-of-4 Selector Switch. Subsequently, All sought a company with an existing technology to leverage previous knowledge and experience to minimize the development effort as well as time to market.

All found a company with a 1-of-4 Switch that could switch mono audio and was controlled via RS-232 serial communications. However, All was having a custom IR (infrared) Remote control designed to integrate the control services of the equipment used in its systems and desired to have the IR Remote remotely control the A/V switch. Additional functionality included terminating S-Video or NTSC composite video on each input and output automatically, switching stereo audio, and up to four remote IR inputs.

Situation
All Communications provides high-end teleconferencing systems to national top 100 companies. This includes the design of the telephony and networking systems required to integrate various multimedia presentation devices including document cameras, conferencing cameras as well as PC’s. All was interested in establishing a brand of its own that would integrate and compliment its systems.

In an effort to add value and reduce cost, All embarked on acquiring a privately branded OEM product, if it existed. This device would be instrumental in the technical integration and control of the various multimedia presentation devices.

All identified a company with a 1-of-4 Switch capable of switching video and mono audio, controlled via RS-232 communications interface. At the same time All was having a custom IR Remote Control device designed and developed to combine the control services of the equipment that was currently used in their systems. Consequently, All desired to have the remote also be capable operating the A/V Switch.

Additional functionality included accommodating either S-Video or NTSC composite video at each input and output automatically, ability to switch stereo audio, and handle up to four remote IR Detector inputs. Lastly, All was looking for a custom enclosure with a high-tech quality look and finish that was comparable to the equipment it sold and installed at customer sites.

Solution
Development of the VS-4 began in the spring of 1999 after it was determined that the identified off-the-shelf OEM switch was not easily nor cost effectively modifiable. A manufacturing cost ceiling was established that drove the requirement for a high level of integration throughout the various subsystems while maintaining the degree of functionality being sought. Couple this with a 60-days-to-prototype schedule and you’ve got a challenge at hand.

The starting questions posed were; how do we handle the fact that either composite video or s-video may be present at any given input? How does Dynazign accommodate either without user intervention? How do we minimize the need to perform extensive multiplexing?
First, Dynazign modeled the sheet metal enclosure and all exterior features such as buttons, power and I/O connectors and indicator lamps. We in turn used this for both virtual proof of concept and generation of pre-sale literature via 3-D photo-realistic rendering. After the enclosure design was approved, we generated the appropriate mechanical drawings and started architecting the electronics.

Second, we selected an appropriate video decoder capable of terminating s-video or NTSC, with six individual video input ports and had a complementary video encoder matched to operate with the decoder. Finally, we needed a video chipset that was low power since our budget was tight for a power supply that met both national and international safety standards.

By devising a scheme of using two s-video cross point matrices optimized for s-video and terminating the NTSC ports directly into the video decoder, we were able to utilize all six input ports into the video decoder chip. The cross point matrix, decoder and encoder were each controlled via I2C interface. Thus, only three lines were required from the processor for the subsystem communications and control. The cross point matrix chips were specifically designed to have available two user-settable bits for driving an audio multiplexed switch and therefore did not require any additional lines from the processor.

Ultimately, only four lines were required to drive the entire 4-to-1-Selector audio and video functions. An additional four lines were used to receive the IR inputs from the remote IR detectors. Level translation was required to terminate the 12V IR Detector input signal since the detectors could possibly be in excess of 100 feet from the switch.

The microprocessor utilized was a low cost PIC microprocessor from Microchip Technologies. The device was capable of capturing real time IR remote input codes while constantly evaluating video input status from the decoder via continuous I2C interrogation. The microprocessor chosen did not have an on-board I2C port and therefore was implemented in firmware. Due to the processing overhead of the I2C routines running continuously, a low overhead finite state machine executive was implemented to guarantee that no asynchronous IR commands would be missed.

Technology & Development
By utilizing a highly integrated video decoder/encoder chipset from Philips Semiconductor, the task of managing either mode of input video was simplified while keeping component count low. In addition, the implied higher quality s-video signal integrity was maintained in lieu of simple wired OR mixing of the chrominance and luminance signals. Using a video cross point matrix and a “clickless” audio mux specifically designed for such an application also helped to keep the parts count to a minimum while simplifying layout requirements.
The PICMicro RISC processor used is among the lowest cost most widely used in industry today. Firmware development was performed using the LabICE 2000 Emulator development system. All firmware application code including all video encoder and decoder initialization code (384 bytes) was stored in the OTP (one-time-programmable) devices.

Power was managed via a combination of a switched inverter (for –5VDC) and distributed isolated low dropout linear regulation (for +5VDC analog & digital, +3.3VDC analog & digital, +8VDC video muxes and +12VDC mains).