Electronic Design

A Digital Sign Of The Times

It should be simple: find a nice large display like Viewsonic’s 37-in N3752w, connect it to a compact motherboard like VIA Technologies’ EPIA EX15000G, and network it with Belkin’s 300Mbps N1 technology. Actually, it is fairly straighforward. But I turned to Logic Supply, a major distributor of Mini-ITX platforms, to find out about the problems and solutions that developers are running into when it comes to digital signage applications. What You See The most obvious component is Viewsonic’s 37-in N3752w HDTV display with a 1366-by-768 resolution. It can support 480i, 480p, 720p, and 1080i video. Video inputs include VGA, HDMI (with HDCP and audio support), composite, component and S-video. There is also a built-in ATSC/NTSC tuner. I liked the latter when testing the system as a TV, since it tunes both digital and analog channels at the same time instead of switching modes manually. The N3752w’s display is impressive. It has a 1000:1 contrast ratio and a viewing angle of 170 degrees. It is relatively bright (500 cd/m2) and the anti-glare, anti-reflective coating improves viewing in bright rooms. I found the N3752w to deliver excellent performance over a range of multimedia content, from movies and television to graphic and slide presentations. The built-in Speakers and dual 10-watt Dolby Digital sound system is sufficient for small- to medium-sized rooms. It can be driven by external inputs including the VIA EX motherboard. An infrared remote is provided and most options are also available from the side-mounted control system. These may be options that developers may want to disable depending upon where the display will be employed. The unit can be wall-mounted using a standard 200mm-by-400mm VESA mount. It is also possible to mount a control unit like the one we built on the rear, but it will not be possible to flush-mount the display on the wall. Of course, it is possible to place the control unit nearby but not immediately adjacent to the display. The N3752w is obviously targeting HDTV home environments but it works equally well for digital signage applications. Hardware Backend The N3752w can be driven from cable input but a more programmatic source using a PC platform. Typically the latter will not have the same peripheral complement unless the systems are employed in a kiosk-style environment. In this particular example we forego the use of keyboards and mice. This is reflected in the case chosen for the task: the Serener GS-L05 case. It has no front-panel connectors. The only thing on the front panel is a pair of LEDs. The rear of the unit exposes the standard Mini-ITX connectors that use a standard cover plate. The GS-L05 Mini-ITX case is designed for fanless operation. Its top cover is finned aluminum. It can handle a range of motherboards like VIA’s EX series used in this system. It requires removal of the normal heatsink that the motherboard is delivered with. This is replaced with a heat pipe system that draws heat away from the processor for dissipation via the cover. As you might have noticed, the configuration requires relatively precise clearances and the interior is tight. That’s where Logic Supply comes into play. I worked with them on system specifics, but had them deliver the actual product. They installed the motherboard, memory and compact power supply (See Tiny Mini-ITX Power Supply) and then added the heat pipe. The power supply has an external power brick as well. The VIA EPIA EX15000G runs a VIA C7 1.5GHz processor with a VIA CX700M2 chipset. It can handle up to 1Gbyts of DDR2 533 DIMM RAM. We used half this amount. The built-in display adapter is the VIA UniChromeTM Pro II 3D/2D AGP graphics with MPEG-2/4 and WMV9 video decoding acceleration. There is an on-board VIA VT1625M HDTV Encoder and the output connectors include a DVI, composite, component and S-video. The VIA VT1708A High Definition Audio Codec can drive the RCA stereo audio outputs or the S/PDIF coaxial or optical connector. I used the RCA stereo and DVI connections for this project since those were cables I had available. The motherboard includes the VIA VT6107 10/100 Mbps Fast Ethernet Controller. A 1Gbit/s Ethernet connection is optional. The motherboard also has a range of internal headers for audio and video. There is an LPC header and a connector for an LVDS panel. The PS/2 interface goes unused and the back panel USB connections were used for the initial software installation and for wireless support. Logic Supply did add a power switch on the back of the unit. I did not take advantage of the 1394 Firewire interface or the pair of SATA interfaces because this was a totally solid-state solution. Instead, Logic Supply installed a 4Gbyte Emphase FDM4000I flash disk in the IDE socket. This not only provides a more reliable system but it can be less expensive. 4Gbytes is more than sufficient for operating systems like Windows XP or Linux with enough free space for a good deal of multimedia content, although not enough for a full-length movie. If you decide to use a wired network you can take advantage of the Ethernet adapter’s PXE boot support. It is possible to set up the boot sequence to use this and fallback to the IDE flash drive. Of course, you might want to put the unit where wired connections are not available, in which case wireless is the way to go. Unfortunately, wireless PXE is not an option so the alternative is to always boot from the IDE flash drive.

Going With A Wireless Sign The EX motherboad has a single PCI slot. Had I used 802.11b/g then Logic Supply would have been able to provide a solution that would work within the confines of the GS-L05 case. Unfortunately I like to push the limits and wanted to stream HDTV content. For this, we turn to the pending 802.11n standard that will push data at speeds in excess of 300Mbit/s. Streaming video to multiple wireless digital signs will easily overwhelm 802.11b/g solutions. Belkin provided their F5D8231-4 N1 Wireless Router for this project. This triple antenna system employs MIMO (Multiple Input Multiple Output) spatial multiplexing. It can push data at speeds up to 300Mbits/s. It supports NAT (network address translation) and it can act as a firewall between a cable or DSL connection and the rest of the network. It incorporates a four port 100BaseT hub. It provided a great way of linking our lab network to the digital signage system. Unfortunately, the F5D8001 N1 Wireless Desktop Card was just a fraction of an inch too high to fit into the GS-L05 case. We did test it with the EX motherboard but you will need to utilize a larger, more expensive case like Logic Supply’s GD-L01. This approach adds space for more and larger hard drives as well as an optical drive, but tends to be overkill for this application. Also, the F5D8001 has external antennas. This not really a problem but makes it comparable to the solution we chose, Belkin’s F5D8051 N1 Wireless USB Adapter. The image shows the adapter with its desktop USB stand. The stand itself contains only the USB cable and connection. We actually used a standard USB extension cable and mounted the actual adapter, with a built-in antenna, to the top rear of the N3752w display with some Vecro. The USB interface is not quite as capable as the desktop card but the differences were not noticeable in our test environment. Still, we expect the desktop card to perform better when the router is a bit farther away. Digital Signage Software The initial setup is most easily done with a USB optical drive attached to the system. It is possible to copy an image onto the flash drive on another system but this tends to be rather tedious in terms of connection since it requires external power. It also means opening the system that Logic Supply sent. A USB keyboard and mouse were used as well. I loaded a stripped-down version of Windows XP for the project. I didn’t pull out my development tools to install Windows XP Embedded although this would likely be a good alternative for this type of application where you do not want someone playing with the system. If you do use a stock version of Windows XP, then make sure you disable the swap file since there is usually no need to thrash the flash memory in this type of application. I also disabled most of the automatic update features and notification since the system will usually run a dedicated signage application that displays data using a fixed script or streams data via the wireless network. Either the Windows XP remote desktop or VNC can be used to provide remote management. This will typically be the mechanism for performing maintenance since the case is normally put in an inaccessible spot without a keyboard or mouse. I also went with Windows XP as a software platform because of driver considerations. Belkin currently has drivers for Windows XP and Vista. Linux drivers may be available but not at the time I started the project. Of course, this would not be the case with the 802.11b/g alternatives including those from Belkin. I actually would have preferred using Linux for this project for its ability to set up a VNC that operates in the background. This would allow changes using a GUI while the main display runs. This can be done using Windows but the setup is a bit more difficult. The other alternative is to use a command line interface like SSH. This is available for both Linux and Windows. Of course, for general user configuration a web interface is the preferred mechanism. Running a web server on Windows or Linux is a trivial exercise. I won’t get into the actual signage related applications because of the variety of options available. It can be as simple as opening an application like Windows media player to stream data via the network connection. Overall, the EPIA EX motherboard has plenty of horsepower to deliver the multimedia content that this type of application requires. The Emphase flash memory proved to be the best option for this type of application. Logic Supply can deliver fully-configured systems made-to-order. All you need to do is add a display. The Mini-ITX approach to digital signage provides a quick way to deliver custom solutions. It’s not the only alternative, but it’s significantly less expensive than building a custom board and system. Related Links Belkin Emphase Logic Supply Microsoft Viewsonic VIA Technologies

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