Sensing device having force and orientation sensors

1. A sensing device comprising:

an image sensor for sensing coded tags disposed on an interactive surface, each coded tag encoding data identifying an orientation of that coded tag;

a force sensor configured to sense a force applied to the interactive surface by the sensing device to generate force data indicative of the force, the force sensor comprising a light source and light detector arranged to detect movement of a stylus used to contact the interactive surface within the sensing device;

a processor configured to generate, using at least one sensed coded tag, indicating data indicative of a rotational orientation of the sensing device relative to interactive surface; and

a transmitter configured to communicate the indicating and force data to a computer system.

2. A sensing device according to claim 1 , further comprising a motion sensor for generating at least one of movement data and position data when the sensing device is moved relative to the interactive surface, wherein the transmitter communicates the movement data to the computer system.

3. A sensing device according to claim 2 , wherein each coded tag further encodes data indicative of a two-dimensional co-ordinate position of that coded tag on the interactive surface, the motion sensor generating the movement and/or position data based on movement and/or position of the sensing device relative to at least one of the coded tag positions.

4. A sensing device according to claim 3 , wherein the motion sensor is configured to sample the position of the sensing device relative to the coded tag position to generate the movement and/or position data.

5. A sensing device according to claim 3 , wherein the coded tags each comprise periodic elements, the periodic elements being substantially identical marks within the coded tags which assist the sensing device in locating the coded tags, the motion sensor generating the movement and/or position data based on movement and/or position of the sensing device relative to at least one of the periodic elements.

6. A sensing device according to claim 5 , wherein the motion sensor is configured to sample the position of the sensing device relative to the periodic elements to generate the movement and/or position data.

7. A sensing device according to claim 1 , further comprising a timer configured to generate time reference data as the sensing device is moved relative to the interactive surface, the time reference data being transmitted to the computer system by the transmitter.

8. A sensing device according to claim 1 , further comprising a stroke detector configured to detect, using the force data, when the sensing device is applied to and removed from the interactive surface, thereby to identify the duration of a stroke.

9. A sensing device according to claim 1 , wherein the orientation sensor is configured to infer the orientation from perspective distortion of at least some of the coded tags.

10. A sensing device according to claim 1 , further comprising memory for storing a unique identifier of the sensing device, wherein the transmitter communicates the identifier to the computer system.

11. A sensing device according to claim 10 , wherein the memory is non-volatile.

12. A sensing device according to claim 10 , wherein the memory is read-only.