The Green School Campaign Phase 2, 2012 to 2014 had slightly different hardware choices - 1) standard / full tower desktops or 2) small form factor desktops (Dell Optiplex). Both were based on PC / Windows (Windows Vista) running Google Chrome. However, both the PC / Windows desktops were using VGA interface.
The VGA (Video Graphics Array) is an analog signal, video only, RGB video, 15 pins, NOT hot pluggable and male connectors at each end that has been with us for more than 20 years. While the transmission bandwidth of VGA is high enough to support resolutions of 1080p and higher, there can be picture quality degradation depending on cable quality and length. A short VGA cable can manage 1920x1080 without trouble. A long VGA cable (up to 5m) may top-out at 1024x768. VGA cables are more susceptible to electrical disturbances and noise compared to DVI or HDMI. Always use high quality cables that provide good, thick insulation. High-end VGA cables with adapters, boosters and / or repeaters can reach 50m in single cable length.
HDMI (High-Definition Multimedia Interface) is a proprietary audio/video interface for transferring uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television or digital audio device. HDMI is a digital replacement for analog video standards. HDMI implements the EIA/CEA-861 (Consumer Electronics Association) standards, which define video formats and waveforms, transport of compressed, uncompressed and LPCM (Linear Pulse Code Modulation) audio, auxiliary data and implementations of the VESA (Video Electronics Standards Association) EDID (Extended Display Identification Data). The HDMI standard is capable of providing high-definition (HD) video at resolutions of 1,920 x 1,200 pixels and 8 audio channels simultaneously. HDMI 1.4 is limited to 4K resolution at 30 FPS and while HDMI 2.0 supports 4K up to 60 FPS. HDMI cables are less sensitive to crosstalk but can suffer interference from electromagnetic fields.
We did our shopping at LowYat Plaza - beware of wide variance in quality! A lot of time (and money) was wasted at work-site due to these DUDS - the packaging LIES!
We selected HDMI V1.4 for all HDMI cables and extenders - these had the best compatibility and quality. HDMI cables of different brands or from different manufacturers show-up in quality and reliability for anything more than 5m.
The HDMI Extender allows you to transmit a Full HD 1080p HDMI signal over Cat6 up to 60m. It includes a sender on one end and a receiver on the other end. Again, HDMI Extenders of different brands or from different manufacturers show-up in quality and reliability when the Ethernet cable length gets more than 30m (just half of the claimed 60m)!
We selected Cat6 / RJ45 for Ethernet cables, up to 50m run and 4 Twisted Pairs i.e. CONNECTING ALL 8 WIRES! Again, Ethernet pre-fabricated cables of different brands or from different manufacturers show-up in quality and reliability in use. We actually got caught with a "Cat6" pre-fabricated cable with only 2 pairs / 4-wires connected, another "Cat6" pre-fabricated cable with only 6-wires connected and yet another another "Cat6" pre-fabricated cable which was more like 30AWG (thin as hair)! The pre-fabricated patch cables were all duds! In the end, we bought cables (PROLINK 24AWG) and RJ45 (Dintek) connectors and crimped the cables ourselves.
Differences Between Categories of Cables : Design, Characteristics
CAT3
|
CAT5
|
CAT5e
|
CAT6
|
CAT6e
| |
|---|---|---|---|---|---|
Maximum Data Rate (1 Twisted Pair)
|
10 Mbps
|
100 Mbps
|
1000 Mbps
|
10 Gbps
|
10 Gbps
|
Maximum Frequency
|
16 Mhz
|
100 Mhz
|
350 Mhz
|
250 Mhz
|
750 Mhz
|
Typical Distance
|
100 m
|
100 m
|
100 m
|
100 m
|
100 m
|
Maximum Distance at Maximum Data Transfer Rate
|
50 m
|
55 m
|
We used an el-cheapo (RM23) Cable / LAN tester to check our cable and connector crimping. This Cable / LAN tester works on continuity test - it just confirms that your crimping is correct.
We were free issued 42" LCD TVs as our monitor. These were either Haier or Sharp brand and came with 2 x HDMI inputs. The settings below allowed us to align the display and fine-tune the borders. It was different for each brand and it was also different when the lengths of the HDMI cable changed!
Since the 1) standard / full tower desktops or 2) small form factor desktops (Dell Optiplex) were installed in Malaysian weather without any air-conditioning, the max setting I used was "config_hdmi_boost=5". I was cautious to NOT overuse the "config_hdmi_boost" parameter as this would cause HIGHER operating temperatures.
Only in 1 site (school), did I set "hdmi_mode=4" (720p, 60 Hz). At this site / school, we were using the HDMI Extender and the Ethernet cable length was ~45m.
In this project, I used commands for ON/OFF of the LCD TVs article as cron scheduled tasks (see Raspberry Pi for Kiosk application). I used the command "sudo tvservice -o" to OFF the LCD TV (the LCD TV goes into standby mode). However, I could NOT ON the LCD TV with the command "sudo tvservice -p". It's a known bug. For now, the workaround is "sudo tvservice -p && fbset -depth 8 && fbset -depth 16 && xrefresh" to re-enable the frame buffer and then force an X11 redraw. Another recommendation was "sudo xset dpms force on". Yet another recommendation was "sudo tvservice -p && chvt 1 && chvt 7" but I have NOT tried any of above.
Extended Display Identification Data (EDIDs) are data structures that reside in a display device - commonly referred to as “sinks” in HDMI and DisplayPort standards documents - such as an HDTV or a computer monitor. They are intended to be read by a “source” device (e.g. set top boxes, DVD players, PC graphic cards) in order to simplify user operation and to ensure that the user’s viewing experience is optimal. EDIDs are stored in an EPROM of an audio or video rendering device. EDIDs were created by Video Electronics Standards Association (VESA) to support “plug and play” on PCs when VGA monitors supported multiple video resolutions. They were then incorporated into consumer electronic devices by the Consumer Electronics Association (CEA). The VESA EDID standard has been updated to support digital PC monitors and HDTVs using DVI, HDMI and more recently DisplayPort. Both VESA and CEA are involved in setting standards for EDIDs.
You can find more information at eLinux.org.
If you want to see all the tvservice command options, just type "tvservice" in Terminal.You can find more information at eLinux.org.
Usage: tvservice [OPTION]...
-p, --preferred Power on HDMI with preferred settings
-e, --explicit="GROUP MODE DRIVE" Power on HDMI with explicit
GROUP (CEA, DMT, CEA_3D_SBS, CEA_3D_TB)
MODE (see --modes) and DRIVE (HDMI, DVI)
-c, --sdtvon="MODE ASPECT" Power on SDTV with
MODE (PAL or NTSC) and
ASPECT (4:3 14:9 or 16:9)
-o, --off Power off the display
-m, --modes=GROUP Get supported modes for GROUP (CEA, DMT)
-M, --monitor Monitor HDMI events
-s, --status Get HDMI status
-a, --audio Get supported audio information
-d, --dumpedid <filename> Dump EDID information to file
-j, --json Use JSON format for --modes output
-n, --name Print the device ID from EDID
-h, --help Print this information
After my project was completed, I found these VideoCore commands for ON/OFF of the LCD TVs which are more efficient (doesn't require the frame-buffer re-initialization and doesn't change the resolution). Furthermore, it is said to be quicker than tvservice.
vcgencmd display_power 0
vcgencmd display_power 1CAUTION: Your circumstances, connections, interfaces, options and versions may differ and needs to be re-evaluated for your specific application.
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