Sensing apparatus

Motion sensing apparatus including at least one light sensitive electronic component, said component responsive to at least a first and second incident light level each level creating in said light sensitive component a first state and a second state, wherein the apparatus is configured to measure the response of the light sensitive component during the first state for at least one of the incident light levels and to compare the response with a previously recorded value.

FIELD OF INVENTION

The invention relates to motion sensing apparatus. More particularly, the invention relates to determining movement of a member by means of the motion sensing apparatus.

BACKGROUND OF THE INVENTION

Electronic devices, for example a cellular handset, a personal digital assistant (PDA), a gaming console or other devices, may be used to handle information, interact with gaming elements and/or to access a communications network. A user will want to interact with the electronic device so as to make or receive calls, send or receive data or interact with software applications.

The electronic device may comprise a display, as would normally be the case for a cellular handset for the displaying of textual or graphical information. The electronic device may comprise a speaker for listening or communicating verbally. The electronic device may comprise a camera for taking images. The electronic device will comprise a user interface so that the user may operate the electronic device.

The functionality present in some electronic devices, for example a cellular handset is increasing, a cellular handset may now comprise a camera, a music player, gaming applications or media related applications. The electronic device must now support different functions and a user interface having only a traditional alphanumeric keypad is not best suited to provide a quick and easy interface between the user and the electronic device, Therefore some user interfaces provide additional input keys such as multi-way navigational key or cylindrical roller body keys, as outlined in EP0901262, which are better suited to navigating menu structures or interfacing with gaining applications. Such navigational keys require their movement or depression be sensed so that items displayed on a display may be activated or browsed.

Navigational keys such as the cylindrical roller key, as outlined in EP0901262, include a mechanical motion sensing means, which permits the user to rotate the key, which may result in a corresponding cursor movement on the display. However in portable electronic devices the overall dimensions must be relatively small to permit the user to carry the electronic device, hence other motion sensing apparatus utilising non mechanical motion sensing apparatus have been adopted.

Motion sensing apparatus as outlined in EP1431713 shows a photo-sensor, comprising a light emitting diode (LED) and a photo-detector, which may be a diode or transistor for the purpose of transmitting and receiving optical signals respectively. Photo-detectors are used for the detection of optical signals and for the conversion of an optical signal to an electrical signal.

The optical signal is directed from the LED to the rotary key input device such that it is reflected from the rotary key towards the photo-detector. The rotary key comprises a plurality of sectors on the surface upon which light is incident, each sector having either a reflective or absorptive characteristic such that as the rotary key is rotated differing amounts of light are received at the photo-detector. Typically, associated circuitry, which utilises the electrical signal from the photo-detector, possibly comprising passive elements such as resistors, biasing elements and transistors may then determine when the rotary key is being rotated by measuring the electrical signal from the photo-detector received over a time period or at a defined time interval and contrasting the measurement with a previous measurement or measurements. Ideally, the electrical signal measured by the associated circuitry due to reflected light from at least two different sectors has a sufficient differential or contrast ratio so that the associated circuitry can determine when the different sectors and therefore the rotary key is being rotated with respect to the photo-sensor. As the rotary key is being rotated the response from the photo-detector as a function of time may look like what is commonly referred to as a ‘square wave’ response. In response to this an electronic device may provide cursor movement on a display or menu browsing in dependence of the rotary movement.

However, the input device must be positioned so as to allow user interaction and will normally be positioned so that it allows freedom of movement, hence there will be an aperture between the electronic device mechanics and the input device near the surface of the mechanical construction of the electronic device. The aperture may allow ambient light to pass and interfere with the photo-detector resulting in an erroneous measurement. Furthermore the mechanical construction of the electronic device may be permeable to light or other EM waves. Ambient light or other EM waves may be able to pass through the mechanical construction and also interfere with the photo-detector. If the motion sensing apparatus is affected by ambient light or other EM waves then the photo-detector may have difficulty in determining when the rotary key input device is being rotated as it may have difficulty in distinguishing when light reflected from the rotary key has been reflected from a reflective or absorptive sector. The contrast ratio between the received light reflected from the two different sectors may be degraded, i.e. it becomes less.

An advantage of the present invention is that there is motion sensing apparatus for determining movement whereby the motion sensing apparatus output is proportional to the intensity of the input energy and said motion sensing apparatus may improve the contrast ratio of the detected energy for different incident energy levels to said motion sensing apparatus.

BRIEF DESCRIPTION OF THE INVENTION

According to one embodiment of the present invention there is motion sensing apparatus comprising at least one light sensitive electronic component, said component responsive to at least a first and second incident light level each level creating in said light sensitive component a first state and a second state, wherein the apparatus is configured to measure the response of the light sensitive component during the first state for at least one of the incident light levels and to compare the response with a previously recorded value;

According to another embodiment of the present invention there is motion sensing apparatus configured to be activated cyclically comprising at least one light sensitive electronic component, said component responsive to at least a first and second incident light level each level creating in said light sensitive component a first state and a second state, wherein the apparatus is configured to measure the response of the light sensitive component during the first state for at least one of the incident light levels and to compare the response with a previously recorded value;

According to a further embodiment of the present invention there is a method for determining motion in an apparatus having a light sensitive component having a plurality of input level dependant dynamic and substantially static states, the method comprising:

measuring a response from the motion sensing apparatus at a time corresponding with the dynamic phase of at least the first or second input signal;

comparing the response with a previously recorded value;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates an exemplary electronic device10which could utilise motion sensing apparatus in accordance with the present invention. A handheld cellular handset, comprising radio reception and transmission means (not shown) built into the casing12of the electronic device10and having an operational facia14coincidental with the front facia15of the electronic device10. It is appreciated that a handheld cellular handset is one exemplifying electronic device10and further embodiments may include, but are not exclusive to, a personal digital assistant (PDA), gaming console, music player and digital camera.

The electronic device10further comprises a display16positioned towards the upper section of the operating facia14and input keys18positioned below the display16. A rotary key20is positioned below the input keys18towards the lower section of the operating facia14; the rotary key20is substantially planar and mounted such that it is perpendicular to its rotational axis, substantial movement of the rotary key being in a plane coincidental with the operational facia14of the electronic device10.

In further embodiments, combinations of the above may be utilised, for example a music player may not have a need for additional input keys18as shown inFIG. 1. Furthermore, positioning and size of the display16and the keys18,20as shown inFIG. 1are exemplary only and may be placed in totality or part on other facias22of the electronic device10. The rotary key20can also be mounted beneath the operational facia14, with part of the circumferential edge of the rotary key20accessible at the side of the electronic device10.

FIG. 2illustrates exemplary motion sensing apparatus in accordance with the present invention. The motion sensing apparatus30is substantially contained within the casing32of the portable electronic device. The motion sensing apparatus30comprising a transmit module34comprising, for example an LED34for the transmission of optical, infra-red (IR) or other electromagnetic (EM) waves; a reception module36comprising, for example a photo-detector for the reception of said waves and a rotary key38which reflects said waves from the transmit module34to the reception module36as illustrated by the transmission path39. In accordance with the present invention the rotary key38may be any moveable member, for example a slideable key (not shown). The transmit34and reception module36will normally be positioned on a PCB40or other support structure (not shown) whereby electrical connections to associated circuitry (not shown) for example biasing circuitry, a processor or memory can be made to and from the said modules (not shown).

The rotary key38has two major surfaces, an upper surface38aand a lower surface38b, which in this embodiment are substantially planar and parallel to one another. The upper surface38amay interface with a user; the rear surface38bfaces away from the user into the body of the electronic device10. The rear surface38bhas a plurality of adjacent sectors44,46in a repeating pattern; a first sector44having a substantially reflective characteristic and a second sector46having a substantially absorptive characteristic. The rotary key38is positioned above the transmit34and reception36modules such that optical, IR or EM waves may be reflected from its rear surface38b. The rotary key is positioned such that the upper surface protrudes through the front facia15of the electronic device10ofFIG. 1to provide ease of movement to said user. The rotary key38may be supported by either a central stanchion42about which the rotary key38may rotate or by the casing32by means of a low frictional interface (not shown) between the casing32and the rotary key38.

Other exemplary motion sensing apparatus (not shown) may comprise a input key located between the transmission and reception modules. The input key having adjacent transparent and opaque sectors where light or other EM waves may be attenuated by the opaque sectors when light is incident upon them as the input key is moved through the light path.

The output of a typical reception sensor e.g. a photo-detector as a function of time is illustrated inFIG. 3. It can be seen that the response51of the photo-detector has two distinct phases, a transient phase50with an associated transient time52and an equilibrium phase54, which occurs after the transient time52. The transient time52being defined by those skilled in the art as the time taken for a device response to go from 10% to 90% of its final output value. The response51of the photo-detector therefore ramps in a substantially positive exponential fashion during the transient time52from a low output to approximately the final output value; the output value during the transient phase being dynamic, i.e. constantly changing. The transient time52is the time it takes for the photo-detector to respond correctly to incident light or other EM waves and is caused by the time it takes for light generated carriers, caused by incident light, within the body of the detector to arrive at and cross its P-N junction. The transient time52is dependant upon the internal structure of the detector and is in part due to the photo-detectors junction capacitance, determination of the transient time52is understood by those skilled in the art and no further consideration will be given.

The equilibrium phase54is substantially static i.e. the response51from the photo-detector does not change providing the biasing and or incident light level does not change.

It is usually advantageous for this transient time52to be minimised as it can be seen fromFIG. 3that the response51from the photo-detector during the transient phase50is erroneous. In systems employing photo sensitive components such as photodiodes or phototransistors measurements will be taken when the component has reached the equilibrium phase54, i.e. following the transient time52when the output of the photo-detector is no longer in error for a given input incident light level. In motion sensing apparatus systems requiring an absolute output level for a given incident energy level it is therefore essential that the transient time be as low as possible so as to avoid any erroneous output as measurements cannot be taken during the transient phase50. It is a further advantage of the proposed invention that the transient time52for the motion sensing apparatus need not be minimised.

FIG. 4shows exemplary biasing circuitry60which may be used with the motion sensing apparatus30illustrated inFIG. 2. The circuitry comprises a photo-sensor module61comprising a light emitting diode (LED)62and phototransistor64. In other embodiments the transmitting and reception elements need not be in the same package but may be separate components, as shown by the transmission34and reception36modules inFIG. 2. For clarity the rotary key38ofFIG. 2has not been included but the transmission path39shown inFIG. 4is the same as that illustrated inFIG. 2. There is also provided a supply voltage terminal66and a ground terminal68. The anode70of the LED62is connected to one terminal72aof a resistor72, the second terminal72bof the resistor72is connected to the supply voltage terminal66. The cathode74of the LED62is connected to the ground terminal68.

The phototransistor64has an emitter terminal80, which is connected directly to the ground terminal68and a collector terminal81, which is connected to what is known by persons skilled in the art as a current mirror82. The current mirror82is used for providing equal current flow along two electrical connections. Its inclusion within the biasing circuitry60is not essential to the invention, so its purpose will only be explained briefly. The current mirror82comprises two transistors, a first pnp transistor83and a second pnp transistor84. The first83and second transistors84having a base terminal83a84a; a collector terminal83b84band an emitter terminal83c84crespectively. The base terminals83a84aare connected together. The collector terminal83band the base terminal83aare connected, as is the collector terminal81of the phototransistor64; the emitter terminal83cis connected to the supply voltage terminal66. The emitter terminal84cof the second transistor84is also connected to the supply voltage terminal66. The collector terminal84bof the second transistor84is connected to a first terminal86aof a resistor86; the second terminal86bof the resistor86is connected to ground68. The purpose of the current mirror82within this circuit is to provide that the same current flowing through the collector terminal81of the phototransistor64also flows through the resistor86. The purpose of the current mirror is to provide a voltage output across the resistor86. It will be appreciated that this circuit could be omitted from any biasing circuitry60in conjunction with the proposed invention, for example a voltage output could be taken at the collector terminal81of the photo-transistor64with the addition of a resistive component or the current mirror82may be replaced by a diode element (not shown) or have additional resistive elements placed between it and the voltage supply terminal66.

FIG. 5illustrates the output voltage response of the motion sensing apparatus ofFIGS. 2 and 4between the first terminal86aof the resistor86and the ground terminal68ofFIG. 4.

FIG. 5aillustrates a first output100of the motion sensing apparatus when transmitted light from the LED62ofFIG. 4has been reflected from an absorptive sector46of the rotary key38ofFIG. 2and is incident upon the phototransistor64ofFIG. 4. It can be seen that the output of the phototransistor64does not reach a substantially static value, previously called the equilibrium phase54ofFIG. 3until after approximately 400 usecs. The output voltage in the equilibrium phase is approximately 130 mV. Also illustrated is a biasing voltage102of approximately 3.6V, which is present on the voltage supply terminal66ofFIG. 4; the purpose of which is to provide a voltage across the LED62ofFIG. 4so that it emits an EM wave.

FIG. 5billustrates a second output105of the motion sensing apparatus when transmitted light from the LED62ofFIG. 4has been reflected from a reflective sector44of the rotary key38ofFIG. 2and is incident upon the phototransistor64ofFIG. 4. It can be seen that the output of the detector does not reach a substantially static value, previously called the equilibrium phase54ofFIG. 3until after approximately 50 usecs. The output voltage in the equilibrium phase is approx. 2.0 V. Also illustrated is a biasing voltage107of approximately 3.6V, which is present on the voltage supply terminal66ofFIG. 4; the purpose of which is to provide a voltage across the LED62ofFIG. 4so that it emits an EM wave.

Contrasting the first output100ofFIG. 5aand the second output105offigure 5bit can be seen that the difference or contrast ratio between the two output levels of the motion sensing apparatus30in response to incident light being reflected from a reflective or absorptive sector is approximately 15:1. This contrast ratio is measured at time t110, which is approximately alter 400 usecs from the sensing apparatus being activated; measured after the output of the detector has reached a substantially static value.FIGS. 5aand5bfurther illustrate that the response time of the motion sensing apparatus60is dependant upon the magnitude of the input incident light.

FIG. 6shows exemplary biasing circuitry160which can be used with the motion sensing apparatus30illustrated inFIG. 2in order to describe the present invention. The reference numerals60-90ofFIG. 4have corresponding reference numerals160-190inFIG. 6. The photo-sensor161as previously described with reference toFIG. 4has a LED162with an anode170and a cathode174. By applying a voltage at the supply voltage terminal166a voltage may beapplied across the LED162and may transmit an EM wave for subsequent reception by the phototransistor164. In addition to the circuitry shown inFIG. 4, a Field Effect Transistor (FET)176has been included in the biasing circuitry160.

The FET176has three terminals, a gate177, a source178and a drain179. The drain179of the FET176is connected to the cathode174of the LED162, the source178of the FET176is connected to ground terminal168. The FET176is used like a switch, when the FET176is activated by means of applying a biasing signal to the gate177there is an electrical short circuit between the drain179and the source178, hence when the FET176is activated current will flow between the voltage supply terminal166and the ground terminal168via the LED162. The LED162will have a voltage applied across it and it will begin to transmit an EM wave. When the FET176is not activated, i.e. there is an open circuit between the source178and the drain179no current will flow between the voltage supply terminal166and the ground terminal168via the LED162. There will therefore be no voltage across the LED162and no EM wave will be transmitted. It will be appreciated by those skilled in the art that other switching elements, e.g. a bipolar transistor (not shown) could be used in order to generate a voltage across the LED162.

By contrasting the biasing circuitry160ofFIG. 6with the biasing circuitry60ofFIG. 4it will be appreciated that in order to activate the LED62ofFIG. 4a voltage has to be applied to the supply voltage terminal66. The biasing circuitry160ofFIG. 6illustrates that applying a voltage to the supply voltage terminal166is not sufficient to activate the LED162, there must also be activation of the FET176. Activation of the LED162can therefore be achieved by applying a suitable biasing signal to the gate177of the FET176or the supply terminal166either simulataneously or when either is biased while the other has been previously biased.

FIG. 7illustrates the output voltage response of the motion sensing apparatus ofFIGS. 2 and 6between the first terminal186aof the resistor186and the ground terminal168ofFIG. 6.

FIG. 7aillustrates a first output200of the motion sensing apparatus30ofFIG. 2when transmitted light from the LED162ofFIG. 6has been reflected from an absorptive sector46of the rotary key38ofFIG. 2and is incident upon the phototransistor164ofFIG. 6. It can be seen that the output of the phototransistor164does not reach a substantially static value, previously called the equilibrium phase54ofFIG. 3. The first output200reaches a maximum voltage of approx. 0.002V. Also illustrated is a control voltage202of approximately 3.6V, which is applied to the gate177of the FET176ofFIG. 6. The control voltage approximates a square pulse of duration forty microseconds.

FIG. 7billustrates a second output205of the motion sensing apparatus30ofFIG. 2when transmitted light from the LED162ofFIG. 6has been reflected from a reflective sector44of the rotary key38ofFIG. 2and is incident upon the phototransistor164ofFIG. 6. It can be seen that the second output205of the phototransistor164reaches a peak value of approx. 2V. Also illustrated is a control voltage207of approximately 3.6V, which is applied to the gate177of the FET176ofFIG. 6. The control voltage207approximates a square pulse of duration forty microseconds.

Contrasting the first output200ofFIG. 7aand the second output205ofFIG. 7bit can be seen that the difference or contrast ratio between the peak output levels of the motion sensing apparatus160in response to incident light being reflected from a reflective or absorptive sector is greater than a 1000:1.

It can be further seen that when the output is recorded during the gated pulse202207for the two incident light levels the contrast ratio is increased further.

Contrasting the first output100ofFIG. 5aand the first output200ofFIG. 7ait can be seen that there is a substantial difference between the two peak output voltages, which are approximately 0.2V and 0.002 volts respectively. Contrasting the second output105ofFIG. 5band the second output205ofFIG. 7bit can be seen that there is little difference between the two peak output voltages which are both approximately 2V.

It can be seen by contrasting the output responses ofFIGS. 5 and 7that the introduction of a switching element, i.e. the FET176ofFIG. 6and corresponding activation of the LED162for a time period by means of the control voltages202,207ofFIG. 7applied to the gate177of the FET176; an improved contrast ratio may result. Said control voltage202,207being shorter in duration than the time needed for the motion sensing apparatus to achieve a static equilibrium state as illustrated inFIG. 5for at least one of the incident input energy levels. An advantageous effect is observed namely that by not permitting the motion sensing apparatus160to achieve a static voltage output the contrast ratio may be improved, i.e. increased; resulting in the motion sensing apparatus becoming more immune to outside interference such as ambient light.

It will also be appreciated that a similar effect would occur if the biasing circuitry ofFIG. 6did not include the FET176and the voltage supply terminal166or the ground terminal168was enabled by the other switching circuitry. For example the gate pulse202ofFIG. 7applied to the FET176could as easily be a voltage pulse applied to the voltage supply terminal166in the absence of the FET176or in addition to the FET control voltage at gate terminal177.

It will also be appreciated that other optical sensors such as photodiodes could replace the phototransistor164ofFIG. 6. Similar biasing circuitry as that outlined inFIG. 6could be used with a photodiode but it is appreciated by those skilled in the art that a photodiode is not as sensitive to optical frequencies as a phototransistor and further amplification and biasing circuitry may be needed.

Having outlined a means by which the contrast ratio between two incident energy levels may be improved application within an electronic device will now be explained.FIG. 8shows the rear surface of a rotary key300comprising an alternating pattern; in this embodiment the pattern comprises substantially reflective302and substantially absorptive304areas but in alternative embodiments (not shown) said pattern may comprise sectors with alternating heights. The operation of the rotary key300has been explained with reference to the rotary key38ofFIG. 2.FIG. 8illustrates three responses305,307,309. A first response305which is the control voltage applied to the motion sensing apparatus ofFIG. 6, as already highlighted this may be applied to a switching element within the apparatus, for example the FET176ofFIG. 6. The first response305comprises three square like pulses305a305b,305ceach of 40 microsecond duration306ahaving a duty cycle306bof approximately 20 milliseconds. These times are typical. A second response307is the output from the motion sensing apparatus ofFIG. 6in response to the rotary key300being rotated. The second response307comprises three pulses307a,307b,307csubstantially coincidental with the three pulses305a,305b,305crespectively. A first pulse307aprovided by said motion sensing apparatus interacting with sector304a, a second pulse interacting with sector302aand a third pulse interacting with sector304b. Pulses307a,307cresulting from said motion sensing apparatus interacting with an absorptive sector of the rotary key300; pulse307bresulting from said motion sensing apparatus interacting with a reflective sector of the rotary key300. Pulses307a,307cbeing substantially lower in magnitude than pulse307b. A third response309is also the output of the motion sensing apparatus ofFIG. 6in response to the rotary key not being rotated, but remaining static. The third response comprises three pulses309a,309b,309csubstantially coincidental with the three pulses305a,305b,305crespectively. All three pulses309a,309b,309cprovided by said motion sensing apparatus interacting with a reflective sector302aof the rotary key300.

It will be appreciated that in the example provided, when a user interacts with a moveable member the rotational movement of the rotary key may be much slower than that indicated above, i.e. there will be many pulses corresponding to response305before there is a change in magnitude as highlighted between the first307aand second307bpulses of response307. The duty cycle306bshould be pre-determined such that motion sensing apparatus30ofFIG. 2is cyclically activated at a rate, which is greater than the movement between the adjacent sectors of said moveable member. Ideally the rate at which the motion sensing apparatus will be activated is at least twice the maximum rate of change between the adjacent sectors.

In an automated device user input may not be necessary and motion sensing apparatus may be used to determine movement which may be much quicker than could be achieved by a user moving a rotary key. The duration of the enabling pulses and the duty cycle should be chosen according to the maximum rate of rotation. It will be appreciated that the examples outlined above are satisfactory for manual movement but may be altered for automated movement.

In a further embodiment motion sensing apparatus30ofFIG. 2may be de-activated in response to an output from said motion sensing apparatus.FIG. 9illustrates the responses of motion sensing apparatus comprising such an embodiment.FIG. 9illustrates rotary key400and three responses405,407and409. The rotary key400is the same as that illustrated by rotary key300inFIG. 8and has corresponding reference numbers400-404respectively. A first response405is the same as the first response305ofFIG. 8and has corresponding reference numbers305-306respectively. A second response407is similar to the second response307ofFIG. 8but there is now a reference level408, which has been set at an exemplary level of 1V. The reference voltage may be any suitable reference level but in a preferred embodiment the level has been set such that it is less than the peak output level from the motion sensing apparatus.

As outlined previously, as the rotary key300is rotated the response from the motion sensing apparatus30ofFIG. 2will result in two pulses each having a different magnitude as outlined by response307407ofFIGS. 8 and 9respectively. A reference voltage level408should be chosen such that it is less than the maximum output response407aand more than the minimum output response407b. This motion sensing circuitry30may determine that a response, which has met the reference level408, has resulted in an optical signal for example being reflected from a substantially reflective area402a. Upon making such a determination there is no need for the motion sensing apparatus30to be biased and may be shut down.

An advantage of using a pre-determined reference level is that the motion sensing apparatus30may be deactivated before the end of the biasing pulse405in order for the hand portable electronic device to conserve current consumption. A further advantage is that the use of the reference voltage level408provides a means of determining which sector light has been reflected from without referring to any previous measurement from a previous cyclical activation.

Response409ofFIG. 9comprising pulses409a,409band409coutlines how a voltage supply rail may be biased in response to the output response407. Contrasting responses405,407and409it can be seen that the motion sensing apparatus32may be de-activated before the end of the control voltage response405ain response to an output response407ain order to save current consumption. The deactivation is seen when the output voltage407aand407creach threshold value408; then the bias voltage as represented by409aand409cis shut off. Since the threshold voltage408is not reached when light is incident on an absorptive region as shown by407b, the bias voltage as represented by409bremains on throughout.

In another embodiment there is motion sensing apparatus, which is responsive to a moveable member comprising a directionally unique sequence of characteristics.FIG. 10illustrates a rotary key500comprising adjacent sectors501,502. . .512. The rotary key500comprising three different characteristics, reflective sectors501,504,507and510; partially reflective sectors502,505,508and511and absorptive sectors503,506,509and512. In alternative embodiments more than three characteristics may be used.

FIG. 10also illustrates three responses520,525and530, which are outputs from the motion sensing circuitry30ofFIG. 2in response to the rotary key38comprising the pattern illustrated by rotary key500being rotated in accordance with the present invention. An upper surface of rotary key500that is visible to a user is identified by reference character500aand a lower surface of rotary key that is not visible to a user is identified by reference character500b. A first response520illustrates a control voltage applied to the motion sensing circuitry ofFIG. 6; the first response520comprising five pulses520a. . .520eof equal duration and constant duty cycle although in alternative embodiments the duty cycle may not be constant and the pulses need not be regular. A second response525illustrates the output of the motion sensing circuitry30ofFIG. 2in response to different incident light levels being received in response to the rotary key500being rotated. Each pulse525a. . .525ebeing coincidental with the pulses520a. . .520eof the first response520respectively. The second response having a first pulse525a, which has the highest magnitude, results form light being reflected from the reflective sector501of the rotary key500. There is a second pulse525bhaving a magnitude less than that of the first pulse525aresulting from light being reflected from the partially reflective sector502of the rotary key500; there is a third pulse525chaving a magnitude less than the first525aand second525bpulses resulting from light being reflected from the absorptive sector503of the rotary key500. There is then a fourth pulse525dwhich is the same as the first pulse525aand a fifth pulse525ewhich is the same as the second pulse525band this pulsing continues while the rotary key500is being rotated. It will be appreciated that the sequence illustrated with the second response525corresponds to a high, medium, low signals which then repeats and this is indicative of the rotary key500being rotated in a clockwise direction.

A third response530illustrates the sequence of pulses530a. . .530ewhen the rotary key500is rotated in a anti-clockwise direction; the sequence illustrated shows a repeating pattern of low, medium, high signals.

In accordance with another aspect of the inventionFIG. 11shows a flow chart outlining a method of operating the motion sensing apparatus ofFIGS. 2 and 6. The operation starts from block600, in which the motion sensing apparatus30is activated.

In block610a measurement is taken at a pre-defined time T1which is less than or equal to the transient time of the apparatus in response to at least one input light level. Block620defines this measurement as ‘new measurement’ and this value can be stored in memory contained within the electronic device10ofFIG. 1for further computation.

In block630the ‘new measurement’ is compared with a previous measurement, which has been defined as ‘previous measurement’. In should be noted that the ‘previous measurement’ corresponds with a measurement occurring during a previous cyclical activation; it could be the last activation or other preceding activation. In alternative embodiments it may be a combination of previous measurements.

In block640upon comparison of the ‘new measurement’ and ‘previous measurement’ a decision is made as to whether the measurements are the same. The comparison may be made on the assumption that the measurements are substantially the same in order to take account of external interference, such as ambient light or other EM interference. In an alternative embodiment the comparison may be made based on pre-defined levels such that the measurements must reach a pre-defined difference before they are not considered as being the same value.

In block650it has been decided with block640by means of the comparison that the ‘new measurement’ is equal to the ‘previous measurement’. Within memory the ‘new measurement’ value is saved as the ‘previous measurement value’; in an alternative embodiment the ‘new measurement’ may be used in combination with other previous measurements in order to determine the ‘previous measurement’ value.

In block660it has been decided within block640by means of the comparison that the ‘new measurement’ is not equal to the ‘previous measurement’. The motion sensing apparatus30will then send an electrical signal to a processor so that this signal may be used in isolation or in combination with other signals, for example from another sensor, that movement has occurred.

As explained earlier the output from the block660flows into the block650and the ‘previous measurement’ value is updated.

In block670the motion sensing apparatus30is de-activated after a time T2. In an alternative embodiment the motion sensing apparatus may be de-activated immediately after a measurement is made in order to save power consumption but the memory and processor tasks may carry on computational tasks.

In block680a delay Td is applied, the summation of the time T2and the time Td are equal to the duty cycle of the motion sensing apparatus. In alternative embodiments the duty cycle may not be fixed but can be variable, this could be achieved with a further input (not shown) in to the block680so as to vary the delay time td. After the delay time Td has elapsed the motion sensing apparatus is re-activated as block600and the cyclic action begins again.