WO2017130004A1

WO2017130004A1 - Colour-changing blocks

Info

Publication number: WO2017130004A1
Application number: PCT/GB2017/050228
Authority: WO
Inventors: Zakir MOHMED; Anthony Kemp; David Lock
Original assignee: Pling Ltd
Priority date: 2016-01-29
Filing date: 2017-01-30
Publication date: 2017-08-03
Also published as: GB2563759A; GB201601725D0; GB201813949D0

Abstract

In a self-enumerating colour-changing block, a processor uses (502) switches to sense a spatial arrangement of the block with respect to another block. An axis selector configures (504) a communication path along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement, so as to form a linear communication network, while supressing communication along any other axes. The linear communication network carries an communication bus, via at least some of the switches and along the selected axis in cooperation with the other block. The axis selector is operable to configure the communication path until a valid input is read from the other block over the path, before the network comprising the bus is formed. In order to use the bus to determine the count of blocks, the processor may receive the count of blocks from the bus. The processor uses (506) the bus to communicate a count of blocks connected to the bus (in a linear chain) along the selected axis. The processor controls the light source to make it change colour (508) in accordance with the determined count of blocks.

Description

COLOUR-CHANGING BLOCKS

The present invention relates to colour-changing blocks and method of self- enumerating illumination of a colour-changing block suitable as a learning resource for children.

Background Art

In the field of numeracy education, objects and images representing rows of blocks have been used as a learning resource for children.

Cuisenaire® rods are typically wooden rods of different colour and length, having a square cross-section, that represent numbers. Cuisenaire rods were devised in the 1920s by Georges Cuisenaire, a Belgian educator. Children learn about number relationships by comparing different collections of rods (e.g. placing an eight rod next to two rods of four). Each number is associated with its own colour. For example, 1 = white, 2 = red, 3 = green, 4 = purple, etc.

A problem with Cuisenaire rods is that they are fixed in the state of colour and number in which they are manufactured. For example a red rod stays red even when placed next to another rod to create a longer rod. The rods cannot be divided up to show the child the effect of subtraction. This means that the child must constantly compare arrangements of rods with other rods.

Digicubes is an app in which horizontal rods are rendered that children can build, break apart and put back together using a touch-screen interface, where rods change colour to keep the same quantity to colour relationship, such as in Cuisenaire rods. In use, a child can drag a single white square, representing a rod of unitary length, onto a working area of a touch screen. When the child drags a second white square and places it to the left or right and adjacent to the first white square, the software detects the arrangement of the squares, calculates that there is a horizontal rod of length 2 and changes the colour of the two squares to red, being the colour related to the number 2. Similarly if a third block is added by the child to either the left or right side of the red rod, then the colour of the extended rod changes to green, being the colour related to the number 3, and so on. As an example of splitting a rod, an orange rod of length 10 can be split, by pressing on and dragging to the right the ninth block along. The resulting rod of length 2 changes colour to red. The remaining rod of length 8 changes colour to brown, being the colour related to the number 8. Although a child can move rods around, they are unable to rotate the squares or rods in the 2-dimensional plane of the screen.

The problem with this 2-dimensional representation is that it does not fully engage the child by allowing the child to manipulate the squares or rods in three dimensions.

Children enjoy imaginative play with physical blocks in three dimensions where they can build tangible structures.

Magnetic toy blocks for building in three dimensions are known. US2006111010 discloses toy blocks held together with rotating spherical magnets. An embodiment of the block has rotatable magnets in the corners.

WO2013/066901 discloses a construction kit comprising building modules, wherein at least one of the building modules is functional and adapted to perform a specific behaviour. In some embodiments, each of the building modules includes at least one connection face adapted to pass either data or power from a first face of a first building module to a first face of a second building module. In other embodiments, each connection face of the building modules is electrically connected with each of the other faces. The kit includes at least one connector adapted to couple the at least one functional module to at least one other module while providing up to three degrees of freedom between the functional module and the at least one other module. The modules may also have components to interact with the physical world, such as an LED. A light/speaker block is disclosed that outputs coloured or white light according to its input.

The problem with the known magnetic blocks is that they do not allow a child to build, break apart and put back together rods of blocks, where rods change colour to keep the same quantity to colour relationship, as for the Digicubes app.

The Digicubes app itself is not usable for physical blocks because it has no way of detecting the arrangement of the physical blocks. Even if provided with an image recognition function to detect the arrangement, it does not have a way of addressing and communicating with the blocks to make them change their colour.

Summary of invention

According to a first aspect of the present invention, there is provided a colour-changing block comprising:

a spatial arrangement sensor operable to sense a spatial arrangement of the block with respect to another block;

a connector, arranged to hold and locate the block to the other block;

an axis selector, operable to configure a communication path along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement, so as to form a linear communication network along the selected axis in cooperation with the other block; and

a processor operable to use the linear communication network to determine or communicate a count of blocks connected to the linear communication network along the selected axis; and

a light source operable to change colour in accordance with the count of blocks. Preferably, the connector comprises a magnet.

Preferably, the connector comprises a plurality of magnets.

Preferably, the axis selector is operable to configure the communication path along the selected axis with respect to the block, while supressing communication along any other axes.

Preferably, the spatial arrangement sensor comprises a plurality of electrical connectors. Preferably, the linear communication network comprises at least some of the electrical connectors. Preferably, the spatial arrangement sensor comprises a plurality of switches.

Preferably, the linear communication network comprises at least some of the switches.

Preferably, the connector comprises a plurality of magnets and the switches comprise the magnets.

Preferably, the connector comprises a plurality of magnets and the magnets are located at corners of the block. Preferably, the axis selector is operable to configure the communication path until a valid input is read from the other block over the path.

Preferably, the processor is further operable to configure a communication path to present a valid pattern on an unconnected face in an opposite direction to the other block along the selected axis.

Preferably, the processor is further operable to transmit over the linear communication network a signal that enables another block to determine a count of blocks connected to the linear communication network along the selected axis.

Preferably, the processor is further operable to:

generate or update a count of blocks connected to the linear communication network along the selected axis, responsive to the spatial arrangement sensor; and

transmit the count of blocks over the linear communication network.

Preferably, the linear communication network comprises a bus. Preferably, the bus comprises an l²C bus or an RS-485 bus. According to a second aspect of the present invention, there is provided a method of self-enumerating illumination of a colour-changing block, the method the comprising the steps of:

sensing a spatial arrangement of the block with respect to another block;

configuring a communication path along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement, so as to form a linear communication network along the selected axis in cooperation with the other block; and

using the linear communication network to determine or communicate a count of blocks connected to the linear communication network along the selected axis; and

operating a light source to change colour in accordance with the count of blocks. Preferably, the communication path is configured along the selected axis with respect to the block, while supressing communication along any other axes.

Preferably, the step of configuring the communication path is performed until a valid input is read from the other block over the path.

Preferably, the method further comprises the step of configuring a communication path to present a valid pattern on an unconnected face in an opposite direction to the other block along the selected axis. Preferably, the method further comprises the step of transmitting over the linear communication network a signal that enables another block to determine a count of blocks connected to the linear communication network along the selected axis.

Preferably, the method further comprises the steps of:

generating or updating a count of blocks connected to the linear communication network along the selected axis, responsive to the spatial arrangement sensor; and

transmitting the count of blocks over the linear communication network. Brief description of drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which:

Figure 1 illustrates, in schematic form, a block in accordance with an embodiment of the present invention.

Figure 2 illustrates, in schematic form, closed and open magnetic switches in accordance with an embodiment of the present invention.

Figure 3 illustrates, in schematic form, a cut-away view of two blocks in contact in accordance with an embodiment of the present invention. Figure 4 illustrates, in schematic form, the electronics in a block in accordance with an embodiment of the present invention.

Figure 5 is a flowchart in accordance with an embodiment of the present invention. Figure 6 is a more detailed flowchart in accordance with an embodiment of the present invention.

Figure 7 is a truth table of the switch states used for sensing the spatial arrangement and configuring the communication path in accordance with an embodiment of the present invention.

Figure 8 shows examples of adding and subtracting with blocks in accordance with an embodiment of the present invention. Figure 9 shows examples of building and fragmenting structures with blocks in accordance with an embodiment of the present invention.

Figure 10 illustrates, in schematic form, a block having a "bull's eye" electrical connector in each face, in accordance with another embodiment of the present invention.

Description of embodiments Figure 1 illustrates a block in accordance with an embodiment of the present invention. The block 100 is a plastic cube that has rounded edges 102 and, at the corners, metal switches 104 containing magnets. The faces 106 of the block are flat.

A partially assembled block 108 is shown, with half of the translucent enclosure 110. Two interleaved PCBs (Printed Circuit Boards) 112 and 114 intersect and have the switches 104 mounted on them, four on each PCB, that is eight in total.

LED (Light Emitting Diode) light sources (not shown) are placed in the centre of the block. There may be two multi-colour LED light sources either side of the main PCB. In order to assist with effective light dissipation the PCB may include cutouts. An internal diffuser may also be provided to dissipate light from source LEDs more evenly across the enclosure.

The block is easy to manufacture and it has a robust construction. The enclosure comprises two identical halves 110 made from injection moulded POM

(Polyoxymethylene), utilising additives including UV (Ultra Violet) stabilisers and blowing agent for stability. All edges are interlocked with the opposing half to improve structural rigidity and LED light dissipation (light bleed though edges). Snap fit is achieved in three places for each half, by snapping around the switch caps in the corners. Using this disjointed construction it is possible to remove tooling draft problems, which introduces the possibility of having external block surface textures and logo detail without the need for complex split tooling or non-perpendicular draft angled faces for mould release. The snap fits may be removed, to reduce injection mould tooling cost, and replaced with one snap fit in the centre hole of each half.

Magnets integrated into the block provide a simple, child-accessible, and safe means of physically connecting cubes together on any of their six faces. Magnets when loose can be a health hazard if a pair are ingested, potentially leading to intestinal

perforation. The design affords complete encapsulation of the magnets and thus avoids possible ingestion by a user. In alternative embodiments, mechanical connectors are arranged to hold and locate a block to another block. The mechanical connectors may be used alone or in

combination with magnetic connectors. Examples of mechanical connectors are peg and hole connectors (like Lego™), hook and loop (such as Velcro™) and jack plugs/sockets. In the latter example, the jack plugs may also provide the electrical connection for the communication bus.

The block 100 is cubic in shape, although other shapes including other polyhedra may be suitable. Figure 2 illustrates closed and open magnetic switches in accordance with an embodiment of the present invention.

Switch 200 is in its closed or on position. Switch 202 is in its open or off position.

The switch 200 comprises an external non-magnetic electrically conductive metal shell 204, a magnetic ball bearing 206 magnetically connected to a magnetized dowel pin 208. Around the dowel pin 208 is a magnetized cylinder 210. Between the magnetized cylinder 210 and the metal shell 204 is an electrically non-conductive polymer insert 212.

The metal shell 204 and magnetized cylinder 210 are both independently soldered to the PCB forming the circuit for the switch. The polymer insert 212 and magnetized cylinder 210 snap fit into the PCBs in eight corners. Using a metal shell advantageously reduces the distance between attached magnetic ball bearings when compared to a polymer shell. This is due to reduced material thickness as a result of improved material strength. The reduced distance increases the magnetic force attracting the blocks together. The rubberized polymer 212 insert advantageously acts as a shock absorber for the PCB when the block impacts a surface on its corner.

The switch 200 is shown activated when the magnetic ball bearing is attracted to a stronger magnetic force than the magnetized cylinder. In this arrangement, the switch 200 is closed, with the conductive circuit from the metal shell 204 to the magnetised cylinder 210 completed by the magnetic ball bearing 206 and magnetized dowel pin 208.

The switch 202 is shown unactivated with the magnetic ball bearing 214 attracted to the magnetized cylinder 216 so retaining the magnetized dowel pin 218 in the magnetized cylinder 216. In this arrangement, the switch 202 is open, with the conductive circuit from the metal shell 218 to the magnetised cylinder 216 not completed by the magnetic ball bearing 214 and magnetized dowel pin 218.

The stronger magnetic force experienced by activated switch 200 can be provided by another adjacent block's magnetic ball bearing, as shown in Figure 3.

Figure 3 illustrates a cut-away view of two blocks 300 and 302 in contact. The switches 200 are closed where the blocks are in contact, by mutual attraction of the magnetic ball bearings 206. The remaining switches 202 remain inactivated and open-circuit.

Figure 4 illustrates, in schematic form, the electronics in a block in accordance with an embodiment of the present invention. All blocks can have the same electronics and same software loaded into their processor. This is advantageous because a child does not have to be concerned with selecting a "master" or "controller" block. If one block is not used, is lost or loses power, then the others will still function autonomously.

The switches are arranged in two banks. The first bank 402 has switches SW1 to SW4. The second bank 404 has switches SW5 to SW8. The switches at the corner of the blocks act as part of a spatial arrangement sensor operable to sense the spatial arrangement of the block with respect to other blocks. The magnets in the switches are arranged to hold and locate the block to other blocks. The combination of magnets and switches into one component reduces the complexity of the system. In alternative embodiments, other spatial arrangement sensors may be used. For example inductive sensors, capacitance sensors, light sensors and/or RFID devices may be integrated in the block. For example, one such sensor can be placed in each face of the block, with six in total able to sense the proximity or contact of a block in each of the six directions of each face. In conjunction with axis selector (for example using the corner magnet caps not as switches to sense spatial arrangement), a proximity or contact sensor on each internal face of the block can provide information to the processor on whether a block has been attached or detached. The proximity or contact sensor can inform the processor that a block has been found or has left a linear chain. The processor would then only respond to information from that and the opposing face.

An use of a proximity or contact sensor in conjunction with axis selector is to provide a checksum. If two blocks were connected or disconnected, the proximity sensor would register this event. It can inform the processor of this event. As the processor has already been informed by the axis selector of this event, it could serve as a checksum.

An example use of a proximity or contact sensor is in detecting shape configuration changes. For groups of blocks assembled into 3D shapes, the proximity sensor may serve as a wake-up sensor. As well as or instead of using the corner magnet caps to poll, once a shape has been in position for a certain amount of time, the blocks would switch off processing and the processor could await the input of the proximity sensor changes before waking up.

The block has an axis selector, in this example implemented with the CD4052 ICs 405 labelled U1 to U4, under control of the processor 406 labelled CPU.

Each CD4052 IC has:

- Inputs X0, Y0, X1 , Y1 , X2, Y2, X3 and Y3 connected to the switches.

- Control inputs A and B connected to the processor.

- Outputs X, Y connected to the processor, e.g. U1 has U1X and U1Y.

The axis selector is operable to configure a communication path between the processor and switches along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement.

Communication along any other axes is supressed. A linear communication network, in this example an l²C bus, is formed via the switches along the selected axis in cooperation with the other one or two blocks adjacent along the axis. Another suitable bus is the standard RS-485 bus, which can implement linear bus topologies using only two wires. To select the axis, the processor applies a binary count to the AB channel select input pins of the CD4052s to configure the communication path until a valid input is read.

The binary count in effect rotates the communication path from the processor to the switches. For a first switch bank, with its switches around a first cube face, the communication path is rotated around an axis extending from the centre of the first face to the centre of the cube. For a second switch bank, with its switches around a second face opposite the first face, the communication path is rotated around the same axis. If the cube is viewed from a direction perpendicular to that axis, one of the other four faces may be viewed face-on. Communication paths from the four switches on that other face, straddling the two switch banks, may be also reconfigured by a binary count being applied to the CD4052s of each of the two switch banks.

Then the l²C bus is formed along the selected axis in cooperation with the other one or two blocks adjacent along the axis. The processor determines whether the l²C bus may be formed along the selected axis by reading the state of the switches. The processor stops the binary count when the state of inputs to the switches is in a valid pattern, as defined in the Data Output column in the table of Figure 7.

It will be appreciated that the linear chain of blocks and linear network may be curvilinear or not in a perfectly straight line.

I²C is a true multi-master bus providing arbitration and collision detection. It uses only two bus lines. In this application, when considering the four corners facing an adjacent block in the linear chain along the selected axis, two switches provide the two bus lines and the two other switches are common. I²C works on a master slave principle, If a master is talking to a slave a line is held low and this is first looked at by other devices on the bus and they will wait until the line goes high. The protocol is designed to allow two or more devices to share a bus so there is no output collisions. A device can be a master or a slave and can changeover mid-stream and have unique addresses which is selected by the master.

The processor 406 in the block is operable to use the l²C bus to determine or communicate a count of blocks connected to the l²C bus (in a linear chain) along the selected axis. The LED light source 408 is operable to change colour in accordance with the count of blocks, under control of the processor.

In order to use the l²C bus to determine the count of blocks, the processor receives the count of blocks from the l²C bus. The processor thus receives a signal using the l²C bus that enables the processor to determine the count of blocks. In the embodiment described with reference to Figures 5 and 6, the signal comprises the count of blocks

In alternative embodiments, the signal may comprise a unique identifier. The unique identifier may be allocated to the block at the time of manufacture. The unique identifier may be generated randomly from a sequence large enough that there is a vanishingly small probability of a matching identifier being generated by another block. In order to use the l²C bus to determine the count of blocks, the processor in a block receives the unique identifiers of other blocks using the l²C bus and counts the number of different unique identifiers received.

In other embodiments, the signal may be unique in its timing rather than its content. For example, the processor may communicate a signal, such as a pulse, with a random timing, so that there is a vanishingly small probability of overlap or confusion with a signal from another block. In order to use the l²C bus to determine the count of blocks, the processor receives the randomly staggered signals from other blocks using the l²C bus and counts the number of distinct signals received.

In other embodiments the processor may use standard network discovery techniques supported by the linear communication network protocol to determine the count of blocks.

The processor also generates or updates a count of blocks connected to the l²C bus along the selected axis, responsive to the state of the switches. After a reset the processor generates a count of 1 if one block is connected and generates a count of 2 if a pair of blocks are connected on either side of the block. In updating a count, the processor updates (increments or decrements) the count of the number of blocks adjacent on the selected axis increases or decreases. In the embodiment described with reference to Figures 5 and 6, the processor then transmits the generated or updated count of blocks to the l²C bus. This is done with the block as bus master and the count is received by the other blocks on the bus (as slaves), which use the value to determine the number of connected blocks. In the alternative embodiments, as discussed above, the processor transmits other signals (such as those having unique content or timing) that enable the processors of other blocks to determine the count of blocks.

Figure 5 is a flowchart in accordance with an embodiment of the present invention. At step 502, the processor uses the switches as a spatial arrangement sensor to sense a spatial arrangement of the block with respect to another block.

At step 504, the axis selector configures a communication path along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement, so as to form a linear communication network, while supressing communication along any other axes. In this example the linear communication network carries an l²C bus, via at least some of the switches and along the selected axis in cooperation with the other block. The axis selector is operable to configure the communication path until a valid input is read from the other block over the path, before the network comprising the l²C bus is formed along the selected axis in cooperation with the other block.

In order to use the l²C bus to determine the count of blocks, the processor may receive the count of blocks from the l²C bus. When the processor determines (in response to the spatial arrangement sensor) that the number of blocks connected to the l²C bus along the selected axis has changed, it generates (setting to 1 or 2) or updates

(incrementing or decrementing) the count of blocks. The first axis chosen by the user by placing the initial pair of blocks (and therefore selected by the axis selector) becomes the 'command' direction for that particular build or play session. That choice determines the colour-changing behaviour in all subsequent directions and choices. At step 506, the processor uses the l²C bus to communicate a count of blocks connected to the l²C bus (in a linear chain) along the selected axis.

At Step 508, the processor controls the light source to make it change colour in accordance with the determined count of blocks.

Figure 6 is a more detailed flowchart in accordance with an embodiment of the present invention. The flowchart of Figure 6 handles one switch bank. The other bank may be handled for example by a parallel branch (not shown) having a copy of steps 616 to 624. If one bank reaches a valid switch state before the other, then it may terminate the other bank's cycling through its switch states.

At step 602, the process starts. At step 604, the processor is in sleep mode. At step 606, if no corner switches are connected, the processor remains in sleep mode 604. Otherwise, at step 608, the processor is awoken from sleep mode by an interrupt. At step 610 the processor initialises and runs the program.

Before a bus connection is set up on a switch bank, a 001 1 pattern is asserted on the switches by pull up/down resistors connected to VDD and VEE on a CD4052. At step 612, the processor receives a block count value from the l²C bus (as slave) and saves the result in the in a block count memory. At step 614, the processor illuminates the block according to the block count value received over the bus. Although steps 612 and 614 are shown at this point in the main program loop, they may be placed at different points or may be in separate routines triggered by an interrupt. Each block is capable of transmitting (step 630 below) and receiving (step 612) the block count value.

At step 616, the processor reads the switch state via the CD4052s of the switch bank, e.g. U1 and U2. At step 618, the switch state at the CD4052 output is tested, in accordance with the valid patterns in the Data Out column in the table shown in Figure 7. If it is not valid, the processor uses CD4052 AB channel select pins to cycle through switch states at step 620. It does this by incrementing a binary count applied to the AB pins of U1 and U2. The switch states correspond to potential communication paths. The processor then loops back to step 616 to read the switch state. Thus the axis selector is operable to configure the communication path until a valid input is read from the other block over the path, before the l²C bus is formed along the selected axis in cooperation with the other block or blocks along the selected axis.

If the switch state is valid, at step 622, the processor establishes an l²C bus on the newly connected face. Cycling through the switch states until a valid input is found thus configures a valid communication path, ready for setting up the bus, so as to form a linear communication network along the selected axis in cooperation with the other block. In an optional step 624, the processor can use the AB channel select pins on the other switch bank to present a valid 0011 pattern on an unconnected face in the opposite direction along the selected axis. The 0011 pattern may be maintained by pull-up and pull-down circuitry connected to the switches. At step 626, the processor determines if the number of adjoining blocks (along the selected axis) has changed. If the number has increased or decreased, then at step 628, the block count memory is incremented or decremented respectively.

At step 630, the processor then transmits the block count value on the l²C bus (as bus master). This step may be skipped if the number of adjoining blocks has not changed.

At step 632, the processor illuminates the block according to the block count value then loops back to step 612 to check the l²C bus (as slave) to determine any further changes to the block count. Once the number of blocks in the l²C bus gets to ten more blocks can be added within the existing colour palette for each number, starting again as it is a base 10 system.

Figure 7 is a truth table of the switch states used for sensing the spatial arrangement and rotating the communication path in accordance with an embodiment of the present invention.

The corner switches in this example are multiplexed by four dual 4x2 multiplexing CD4052 ICs labelled U1 to U4, Two banks of switches (four per face) are fed to a PIC processor (CPU) via these multiplexers. Each set of switches are independently controlled by the AB channel select control inputs of the multiplexer. The Y and X outputs of the multiplexer are read by the processor in the following manner for the switch bank comprising U1 and U2. U1Y = Switches 1234 (0011 )

U2X = Switches 2341 (0110)

U2Y = Switches 3421 (1100)

U1X = Switches 4123 (1001 ) Resistor arrays act as pull up and pull down levels for the switches to set the bit patterns shown in brackets above. The PIC is firstly initialised as inputs to read the switch configurations and when a valid state is established by the multiplexer control lines the two least significant data bits are configured as data and clock lines for the l²C bus.

The truth table for the multiplexers is shown in Figure 7 and only one switch bank is described since the other is similar except the rotation of the multiplexer is reversed. Figure 7 illustrates how the operation of the control lines configures the switches. The enable feature of the multiplexers (Pin 6 in a CD4052) can be connected to an output on the PIC CPU. When an invalid state occurs, the corresponding face of the block can be electrically isolated by the PIC. Because the switches have pull up and pull down resistors it can be useful to avoid level collisions hence the function of isolation is used. When the Enable line is held high all four multiplexer inputs on the eight pins XO, YO through to X3, Y3 are isolated from the outputs X and Y.

Figure 8 shows examples of adding and subtracting with blocks in accordance with an embodiment of the present invention. In Figures 8 and 9, the blocks are labelled with the colour number, thus 1 is white, 2 is red, etc.

Blocks 802 illustrate 2+1 =3. Blocks 804 illustrate 4+8 = 10+2. Blocks 806 illustrate 5-1 = 4 by splitting the rod of length 5 along the dotted line. Similarly, blocks 808 illustrate 5-2 = 3.

Figure 9 shows examples of building and fragmenting structures with blocks in accordance with an embodiment of the present invention.

Blocks 902 illustrate adding one block to a rod on a disallowed axis. The rod of length 3 stays illuminated with the colour for 3, while the added block stays with the colour for 1. Similarly, blocks 904 illustrate adding one block to a rod on a disallowed axis. The rod of length 2 stays illuminated with the colour for 2, while the added block and other disallowed block stay with the colour for 1. Blocks 906 illustrate the addition of a rod of 2 forming a new rod of length 3 at the right hand side of the structure.

Blocks 908 illustrate the fragmenting of a structure, shown by the dashed line. The blocks renumber themselves in the configurations shown at the right-hand side with four rods of length 2 and one of length 1.

Advantages of the embodiments described above are as follows. The blocks have an attractive simple form. Light diffusion across the whole of each face is achieved, increasing the educational value. The magnetic attraction of the corner magnets allows multiple blocks to be held in the air using relatively small magnets. Supporting one block in the air, aided only by the magnetic attraction of adjacent blocks, can be achieved with a low magnet to weight ratio. The block is easy and reliable to

manufacture. Figure 10 illustrates an alternative embodiment with a "bull's eye" electrical connector in each face. The block 1000 is a plastic cube that has rounded edges and, at the centre of each face, electrical connectors 1002, 1004, 1006 each arranged in bull's eye configuration. Insulating regions 1008, 1010, isolate concentric conductors 1012, 1014. The respective bull's eye connectors of blocks held and located together make an electrical connection when brought into contact.

The conductors 1012, 1014 are routed to control inputs A and B connected to the processor, as described with reference to Figure 4 above. Also as mentioned above, RS-485 may be used to implement the linear bus topology using only two wires. This is because RS-485 drivers use three-state logic. Therefore the same axis selection system described with reference to Figure 4 may be used. The communication is supressed on faces 2,3,4,5 after connection made on face 1 , so that face 6 (that is opposite face 1 ) is the only acceptable next input on the linear bus. Thus only opposite faces are valid. Although the magnets are not involved in communication, they may be involved in power-saving (by detecting proximity) and/or as spatial arrangement sensors. The bus may be for example either l²C or RS-485.

The spatial arrangement may be sensed using the conductors 1012, 1014 themselves by detecting an electrical connection of the conductors with another block. Alternatively or additionally, spatial arrangement may be senses by other sensors in the block, such as magnetic switches, inductive proximity sensors or RFID proximity sensors.

The bull's eye electrical connector can be used with block connectors such as magnets or mechanical connectors, as discussed herein, arranged to hold and locate blocks together. The connectors holding and locating the blocks together may for example be internal magnets in the corners or magnets in the centre of each face. The magnets do not need to be visible or form part of the electrical contact in this embodiment. The bull's eye configuration is rotationally symmetric, so a connection can be made between blocks held and located together by a connector, whatever the rotation of one block relative to the other along the axis passing through the centres of the two blocks.

Claims

1. A colour-changing block comprising:

a connector, arranged to hold and locate the block to the other block;

a light source operable to change colour in accordance with the count of blocks.

2. The block of claim 1 , wherein the connector comprises a magnet.

3. The block of claim 1 or claim 2, wherein the connector comprises a plurality of magnets.

4. The block of any preceding claim, wherein the axis selector is operable to configure the communication path along the selected axis with respect to the block while supressing communication along any other axes.

5. The block of any preceding claim, wherein the spatial arrangement sensor comprises a plurality of electrical connectors.

6. The block of claim 5, wherein the linear communication network comprises at least some of the electrical connectors.

7. The block of any preceding claim, wherein the spatial arrangement sensor comprises a plurality of switches.

8. The block of claim 7, wherein the linear communication network comprises at least some of the switches.

9. The block of claim 7 or claim 8, wherein the connector comprises a plurality of magnets and the switches comprise the magnets.

10. The block of any preceding of claim, wherein the connector comprises a plurality of magnets and the magnets are located at corners of the block.

11. The block of any preceding claim, wherein the axis selector is operable to configure the communication path until a valid input is read from the other block over the path.

12. The block of claim 11 , wherein the processor is further operable to configure a communication path to present a valid pattern on an unconnected face in an opposite direction to the other block along the selected axis.

13. The block of any preceding claim, wherein the processor is further operable to transmit over the linear communication network a signal that enables another block to determine a count of blocks connected to the linear communication network along the selected axis.

14. The block of any preceding claim, wherein the processor is further operable to: generate or update a count of blocks connected to the linear communication network along the selected axis, responsive to the spatial arrangement sensor; and

transmit the count of blocks over the linear communication network.

15. The block of any preceding claim, wherein the linear communication network comprises a bus.

16. The block of claim 15, wherein the bus comprises an l²C bus or an RS-485 bus.

17. A method of self-enumerating illumination of a colour-changing block, the method the comprising the steps of:

sensing a spatial arrangement of the block with respect to another block; configuring a communication path along a selected axis with respect to the block, the selection being responsive to the sensed spatial arrangement, so as to form a linear communication network along the selected axis in cooperation with the other block; and

operating a light source to change colour in accordance with the count of blocks.

18. The method of claim 17, wherein the communication path is configured along the selected axis with respect to the block while supressing communication along any other axes.

19. The method of claim 17 or claim 18, wherein the step of configuring the

communication path is performed until a valid input is read from the other block over the path.

20. The method of claim 19, further comprising the step of configuring a communication path to present a valid pattern on an unconnected face in an opposite direction to the other block along the selected axis.

21. The method of any of claims 17 to 20, further comprising the step of transmitting over the linear communication network a signal that enables another block to determine a count of blocks connected to the linear communication network along the selected axis.

22. The method of any of claims 17 to 21 , further comprising the steps of:

transmitting the count of blocks over the linear communication network.