The bench test 1: It takes two!

Together with the video monitors and entry panel, Comelit supplied two dedicated power supply units, the 1195 and 1246, plus the data/power mixer interface 4896 and numerous branch terminal modules, part 1214/2. For the purposes of the test, we used one video monitor handset and one audio-only handset.

   Two separate PSUs are necessary to power the Simplebus 2 system – the first, part 1195, feeds the front door panel plus the electric release and the other, part 1246, drives the Simplebus network, including the data/power mixer, audio handsets and video monitors.

   Both PSUs are 240v mains supplied, stepping down the operating voltage to a combination of low AC values. So the system has no capacity to operate during mains power failure.

Each PSU is compact and easy to wall mount, using a European style DIN rail to fix to the wall surface. Curiously, only the 1195 unit was supplied with a DIN rail, though this may have been an oversight by Comelit. Each of the connection terminals are protected by a screw-fixed cover plate, but as usual these do not allow for a great deal of spare wiring to be concealed within the unit. This may possibly be a problem over a period of years as the wires are disconnected, tested and reconnected during the life of the system. The covers do protect the mains terminals effectively and safely.

Each of the three output components, including the data/power mixer, is protected by internal electronic fuses. In the event of overload or short circuit they are re-settable by clearing the fault condition followed by down-powering for a short period. The measured AC voltage outputs were found to be slightly higher than described in the manual, though this should not present a problem. There are no user adjustable potentiometers to 'tweak' the voltages for longer or shorter cable runs, so installers will need to adhere to the table of operating distance versus cable type as given by the manufacturer, again in the manual. There are no on-board LEDs to give power output confirmation to users.

   Comelit manufactures a range of speech panel types, including a vandal resistant finish. Our supplied kit is called the 'powercom' type, and is a modular construction of call buttons, camera modules and speech units combined and fixed into a housing frame and finished with a metal surround to tidy up the arrangement.

Each of the call buttons has a translucent cover to allow a nametag to be inserted. They are unusual in that they are backlit by blue (!) LEDs. Not to everyone's taste, but certainly different.

The speech/camera module has a louvered arrangement of holes to allow for clarity of sound while giving some protection from the weather. The on-board camera uses a fixed focus lens with a ¼-inch CCD chip giving 'medium' resolution at 300 TVL. Comelit has wisely included a set of six 'black' LEDs surrounding the lens to illuminate the subject matter during darkness. Aesthetic quality is always subjective, but we found the overall package of a chrome speech module, blue plastic call buttons and a diecast stove-finished metal surround to be less than harmonious. Italy: nil points, as Katie Boyle might say.

This being a two-wire system, installers would be forgiven for thinking only two conductors are necessary to feed the front door panel. Wrong.

The system power must be supplied separately from PSU1195. Furthermore, the electric release wiring pair is also driven by the speech panel, necessitating two more conductors in place from panel to electric lock. In practice though, this is not usually a problem due to their proximity (a good reason to locate the front door panel adjacent to the opening edge of the front door).

   The audio handset is a standard vertical wall mount type in cream coloured ABS plastic finish. The unit comes complete with a lock release button and one further face mounted button to connect to other services, such as lighting relays or an additional electric door release.

The printed circuit board includes two potentiometers to trim the microphone output level and, very usefully, call tone volume. (How many times have you finished an installation to be told by the customer the call tone is too loud, or indeed too quiet?) Comelit: dix points, as Katie would be happy to concede.

The square design has a lightweight plastic feel, and looks how door entry telephone handsets have looked for the past 20 years. The video handset is naturally a larger device that snap-fits on to the wall mounted backplate containing the connection terminals and the Simplebus interface components. The video screen is mono and measures four inches diagonally across. The picture can be called up manually by pressing the correct button, and remains in view for approximately 80 seconds.

It is also a beast, with unnecessarily spaced out press buttons and a dull, unpleasing look that, again, is loosely based on every other video handset you have seen in the past 20 years. The camera illumination LEDs operate at a wavelength beyond the range of human sight (i.e. they do not give off any red light) and were found to be effective in complete darkness to a range of about 1.5m. That is just adequate since the camera and four-inch mono screen on the hand-set are medium resolution devices and are too small to make sense of anything further away than that.

We set up the equipment using short lengths of single core alarm cable wiring, even though the installation manual gives a tabulated scheme of all the possible types of cable that can be used: standard telephone twisted pair; shielded twin cable; CAT 5e unshielded twisted pair; 1.5mm mains twin & earth. They all work well, even 'figure of eight doorbell' type cable, which raises the question: can this system be used to replace and upgrade a conventional doorbell to a video entry system without re-wiring the premises? Answer: er … almost. That is providing the cable runs are not too long and notwithstanding the earlier mentioned requirement to power the front door panel with an additional feed pair.

The speech quality was fine, with no discernible hum or interference, and a good balance of internal/external volume levels was achievable using the trim 'pots' in the handsets and speech module. The equipment does not include a 'privacy of speech' function, so end users should be made aware that their conversations can be heard by anyone who chooses to pick up a handset. Overall, the team felt that the equipment was well conceived and worked adequately but was let down by poor aesthetic design. The main system overview, wiring diagrams and component descriptions are contained within the Simplebus 2 'Bible' (the MT/SB2/01), available in seven languages.

The English section lies second (after the Italian section of course) and comprises 20 pages. You wouldn't think a set of instructions for a two-wire video entry system could be stretched as far as 20 pages of A4 sized paper. That's not to mention the booklet that accompanies each component part, of at least four pages of A4 paper. The explanations are good, but no troubleshooting advice is provided.

What the manufacturer says ...
IN 1999 Comelit group began cutting installation costs by reducing cabling and termination time and making the job of the installer easier without compromising the quality of the products. The result was Simplebus door entry, a patented system based on two-wire digital technology.

This system not only allows you to carry out new installations in the easiest and quickest way but also allows you to replace existing bell or audio systems by video entry without replacing the existing cabling infrastructure. In the past few years Simplebus has been copied but so far all the two-wire systems on the market require either a local power supply unit connected to the monitor or a central power supply unit plus two additional wires in the riser which is not therefore a true two- wire system.

Simplebus 2 is a genuine two-wire system, power supply of the monitors included. With Simplebus 2 it is possible to carry out video door entry systems where the monitors and handsets are connected with only two wires. The two wires (which are non-polarised and do not necessarily have to be twisted) carry not only the audio and video signals, but also data and power for the monitors. This revolutionary technology allows you to further reduce both the cabling and the equipment costs as well as the number of wires required. In addition, a handset can easily be replaced by a monitor in mixed door entry systems.

Concierge switchboards, no limits to system configuration and a large choice of entry panels make Simplebus 2 a flexible and highly performing system, suitable for any kind of door entry installation.