An example of a system according to the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a shelf with a ribbon-like conductor along its edge and display devices associated therewith; and

Figure 2 is a perspective view of a conventional carrier strip capable of accepting a paper label and/or a ribbon-like conductor strip.

In the embodiment shown in the Figures, the ribbon 1 includes two parallel flat conductors that act as capacitor plates 2, the other halves of the capacitors being formed by suitably sized plates 3 provided in an electronic display unit 4, as seen in Figure

1. These plates 2, 3 are arranged to form the electrical circuit shown. By suitable electrical stimulation of the shelf edge plates

2, power and/or data may be transferred to the display unit plates 3, provided they are in close proximity. Clearly the form of the stimulation may be modulated in terms of frequency, amplitude or phase to carry said data.

The shelf edge capacitor plates 2 are preferably formed by a film of a conductive material applied to a thin substrate of an insulating material. Suitable insulating materials include synthetic plastics materials, as well as the traditional paper-like materials. An effective and low cost means of applying the conductive element forming the plates or plates 2 is to use printing techniques with conductive ink.

A conventional paper shelf edge label, on which price information can be written or printed, is about 30mm by 70mm. Such a label could be replaced by a ribbon conductor approximately 30mm wide

extending along the shelf edge in the carrier originally installed to carry the conventional labels. The ribbon conductor is wide enough to support two plates 2 of 12mm width, spaced by 2mm from each other and from the edges of the ribbon. By providing capacitor plates 3 on the display unit which are 12mm wide and 70mm long, and using an air gap of 1.5mm between the plates 2 and 3, then a capacitance of about 20 pF would exist across the plates. There are thus two capacitors effectively in series in the circuit giving a usable capacitance of lOpF. If the stimulation frequency were set at 32 kHz then the capacitive reactance would be about 0.5 HOhm allowing at least 6 uAmps to flow given a 3 Volts r s amplitude input. This approximate calculation shows that it is possible to also pass power to a display device provided that it incorporates low power electronics, CMOS and LCD technology for example.

Since the capacitive coupling is loose, the quantity of power that can be transferred is limited so that if the display device requires a lot of energy it must be self powered and the primary function of the plates 2 and 3 is to serve as a data channel only.

A beneficial arrangement of a complete system would be to have the display units designed as slave devices to a master device that manages the whole shelf edge. The master device would be responsible for handling communications with the main system controller and could employ any of the extant techniques for this purpose. Information would be relayed to the slave units by use of the contactless bus. The bus could also provide a path for the slave devices to suitably acknowledge the reciept of messages back to the master. In essence a two way communications channel from slave to master will be effected.

There are numerous existing designs of paper-carrying shelf edge label carriers, and thus the ribbon conductor would have to be designed to suit in each particular case. In the instance where the carrier is an integral part of the shelving metal work, the ribbon conductor could be applied in a self-adhesive form. This technique

would also be employed where there is no special adaptation of the shelf edge to take a paper label and where the labels are placed into individual plastic mouldings that simply clip to the shelf facing edge.