referring firstly to fig1 and 2 , in a first embodiment of the invention a banknote validator 2 comprises a compact , box - like housing 3 having first , second , third and fourth lateral sides 2 a , 2 b , 2 c , 2 d , a proximal end 2 e and a distal end 2 f . the housing is comprised of components which are moulded from a durable plastics material . essentially the validator comprises three major moulded modules which are described below . the banknote validator 2 comprises a banknote receiving portion 4 for receiving banknotes ( banknotes not shown ), which represents a first major moulded module , and a banknote acceptance portion 6 for validating and dispensing received banknotes to a long term store ( not shown ), which represents a second major moulded module . the banknote receiving portion 4 and the banknote acceptance portion 6 are pivotally connected together via two hinges 8 , as will be explained in detail below . in fig1 and fig2 , the validator 2 is shown in an open position , with the banknote acceptance portion 6 pivoted away from the banknote receiving portion 4 . the banknote receiving portion 4 comprises a mask or bezel 10 having an oblong front face 12 best seen in fig1 . the front face 12 is proximal , i . e . faces users of the banknote validator 2 , and comprises an oblong banknote receiving ( or input ) slot 14 which defines an opening of a banknote path ( or pathway ) 16 along which banknotes travel into and within the banknote validator 2 in use . the receiving slot 14 is located in an oblong proximally raised section 18 of the front face 12 , so as to be visible and accessible to users when the banknote validator 2 is mounted in a vending machine or the like ( not shown ). depending on the design of the vending machine , the raised section 18 of the front face 12 may be the only part of the banknote validator 2 that is visible when the validator 2 is mounted . referring to fig1 , fig2 and fig3 , first second , third and fourth forward side walls 20 a , 20 b , 20 c , 20 d of the bezel 10 respectively extend distally from the oblong front face 12 , to give the bezel 10 a distally open , box - like shape having an interior cavity 22 . the forward side walls 20 a , 20 b , 20 c , 20 d comprise a number of formations 24 for locating and securing the banknote validator 2 during mounting . additionally , the first side wall 20 a comprises a pocket 26 having a slit 28 for engaging a clip 30 of the banknote acceptance portion 6 as will be described later , whilst the third side wall 20 c supports two bearings 33 , which each form part of one of the hinges 8 . the second and fourth side walls 20 b , 20 d comprise respective outwardly raised flaps 34 , 36 , that extend distally and aid sealing and location of the receiving portion 4 with respect to the acceptance portion 6 as will be described . the flaps 34 , 36 comprise internal locating projections 37 . one function of the bezel 10 is to house internal components of the validator 2 within the banknote receiving portion 4 . with reference to fig2 and 3 , the main components that are housed within the bezel 10 of the banknote receiving portion 4 are : a banknote receiving channel 38 defining the banknote path 16 in the banknote receiving portion 4 , a pair of drive wheels 40 , 42 for gripping and transporting banknotes along the banknote path 16 in use , and a transmission 44 for driving one of the drive wheels 40 . the banknote receiving channel 38 is a rigid tube that is integral with the bezel 10 and extends distally from the receiving slot 14 in the front face 12 of the bezel 10 up to an interface 46 with a banknote acceptance channel 48 of the banknote acceptance portion 6 . the banknote acceptance channel 48 forms the third major moulded module and will be described in detail later . together the banknote receiving channel 38 and the banknote acceptance channel 48 form an enclosed conduit through the banknote validator , which defines the complete banknote pathway 16 through the validator . the banknote receiving channel 38 is oblong in cross section and has a comparatively great width , defined by the distance between first and second lateral walls 38 b , 38 d , and a comparatively small height defined by the distance between first and second major walls 38 a , 38 c . the banknote receiving channel is thus designed to define and encapsulate the banknote path 16 and closely match the dimensions of the banknotes which can be conveyed and guided along the banknote path 16 . whilst the width of the channel 38 is substantially uniform throughout , its height is tapered in the region of the receiving slot 14 , decreasing distally from the slot 14 , before reaching a constant value , thereby having a funnel - shape . this assists in guiding the insertion of the banknote into the validator . the lateral walls 38 b , 38 d of the banknote receiving channel 38 , which act as guide surfaces ( or guide means ) for banknote edges , are seamless between the receiving slot 14 and the interface 46 . at the interface 46 the major walls 38 a , 38 c of the banknote receiving channel 38 comprise jagged ( toothed ) edges 50 that are arranged to complement and cooperate with associated jagged ( toothed ) edges 52 of the banknote acceptance channel 48 of the banknote acceptance portion 6 . the major walls 38 a , 38 c of the banknote receiving channel 38 also comprise cut outs 54 provided along the direction of the banknote path for accommodating the wheels 40 , 42 and a light guide 56 of the banknote acceptance potion 6 , as will be described in detail below . the cut outs 54 for accommodating the light guide 56 are longer than the cut outs 54 accommodating the wheels 40 , 42 so that the tip of the light guide 56 is closer to the receiving slot 14 than the nip of the wheels 40 , 42 . the insertion of a banknote can thus be sensed by the validator 2 via the light guide 56 before the banknote reaches the nip of the wheels 40 , 42 . the lateral walls 38 b 38 d of the banknote receiving channel 38 comprise substantially straight edges 58 oriented perpendicularly to the banknote path 16 at the interface 46 . the pair of wheels 40 , 42 serve to transport banknotes along the banknote receiving channel 38 in use . the pair 40 , 42 comprises a first , drive wheel 40 and a second , idler wheel 42 . the first and second wheels 40 , 42 are biased towards each other so that they are able to grip banknotes between them . the wheels 40 , 42 are provided on spindles ( or axles ) which are respectively supported by protrusions on the bezel 10 , on either side of the banknote receiving channel 38 . each wheel 40 , 42 is accommodated by a respective central slit 54 in an associated major wall 38 a , 38 c of the banknote receiving channel 38 . the pair of wheels 40 , 42 thus accesses the banknote path 16 centrally at an equal distance from both lateral walls 38 b , 38 d , to contact the grip banknotes therein . the pair 40 , 32 is positioned close to the receiving slot 14 and is thus able to grip and transport banknotes along the banknote path 16 even when they are only partially inserted into the banknote path 16 via the receiving slot 14 . also the provision of a single pair of wheels 40 , 42 centrally to the banknote path 16 enable the pair of wheels 40 , 42 to act as a pivot point for a gripped banknote which has been inserted at an angle to the correct direction of travel along the banknote path 16 . the provision of the pivot point , particularly together with the seamless side walls 38 b , 38 d of the banknote receiving channel 38 enable correction of such misalignment . the driven wheel 40 is actuated via the transmission 44 . the transmission 44 comprises : an extended axle 57 between the drive wheel 40 and a first cog 59 that is mounted on the fourth forward side wall 20 d ; and a second cog 60 that is mounted on an associated one of the flaps 36 and is in cooperation with the first cog 59 . the second cog 60 extends distally beyond the fourth side wall 20 d and is shielded by the flap 36 . driving of the second cog 60 by a drive mechanism 88 ( provided in the banknote acceptance portion 6 ) results in movement of the driven wheel 40 , via the first cog 59 and the axle 57 . referring now to fig1 , fig2 and fig4 , the banknote acceptance portion 6 comprises a case 62 of box - like shape , which is distally open . the case comprises first , second , third and fourth rearward side walls 64 a , 64 b , 64 c , 64 d that correspond in plan to , and align with , the distal ends of the forward side walls 20 a , 20 b , 20 c , 20 d of the banknote receiving portion 4 , and which support a rear plate 66 of the case 62 at their distal ends . the rear plate 66 comprises a distally raised section 68 , having a banknote acceptance ( or exit ) slot 70 that defines an exit of the banknote path 16 . the first rearward side wall 64 a comprises the proximally extending clip 30 which is engagable with the slit 28 in the pocket 26 of the first forward side wall 20 a in a snap fit . the third side wall 64 c supports first and second posts 72 which are engageable with the bearings 33 of the banknote receiving portion 4 to form the hinges 8 . finally , the second and fourth rear side walls 64 b , 64 d comprise external ridges 74 for locating the outwardly raised flaps 34 , 36 of the banknote receiving portion 4 , and indentations 78 for accommodating internal locating projections 37 of the flaps 34 , 36 and the second cog 60 of the transmission 44 of the banknote receiving portion 4 . a number of internal components of the banknote validator 2 are held within , or supported by , the case 62 of the banknote acceptance portion 6 . these components include : the banknote acceptance channel 48 defining the banknote path 16 within the banknote acceptance portion 6 ; banknote sensing means for sending and validating banknotes in the banknote path 16 ; two pairs of wheels 80 , 82 , 84 , 86 for transporting banknotes along the banknote path 16 ; and a drive mechanism 88 for driving two of the wheels 80 , 84 and the second cog 60 of the receiving portion 4 . referring to fig4 and fig5 a and 5 b , the banknote acceptance channel 48 mirrors the shape of the banknote receiving channel 38 , being a rigid tube that extends proximally from the banknote acceptance slot 70 in the rear plate 66 of the case 62 up to the interface 46 with the banknote receiving channel 38 of the banknote receiving portion 4 . the acceptance channel 48 is oblong in cross section and has a comparatively great width , defined by the distance between first and second lateral walls 48 b , 48 d lying next to the second and fourth rearward side walls 64 b , 64 d respectively , and a comparatively small height defined by the distance between the first and second major walls 48 a , 48 c . whilst the width of the channel 48 is substantially uniform throughout , its height is tapered in the region of the acceptance slot 70 , decreasing proximally from the slot 70 , before reaching a constant value . the banknote acceptance channel 48 is therefore funnel shaped at one end . one function of the banknote acceptance channel 48 is to define the banknote path 16 within the banknote acceptance portion 6 and to guide banknotes travelling along the banknote path 16 in use . the lateral walls 48 b , 48 d of the banknote acceptance channel 48 , which acts as guide surfaces for banknote edges , are seamless between the interface 46 and the acceptance slot 70 . at the interface 46 the major walls 48 a , 48 c of the banknote receiving channel 48 comprise jagged ( toothed ) edges 52 that are arranged to complement and cooperate with associated jagged ( toothed ) edges 50 of the banknote receiving channel 38 of the banknote receiving portion 4 . the major walls 48 a , 48 c also comprise apertures 90 for accommodating the guide wheels 80 , 82 , 84 , 86 of the acceptance portion 6 . the lateral walls 48 b , 48 d of the banknote acceptance channel 48 comprise substantially straight edges 92 oriented perpendicularly to the banknote path 16 at the interface 46 . the banknote acceptance channel 48 also plays an important part in the sensing of banknotes by the banknote validator 2 . in contrast to the banknote receiving channel 38 , the banknote acceptance channel 48 is a translucent moulded object and acts as an integrated optical element that combines with a circuit board 98 to sense the validated banknotes . referring to fig5 a and 5 b , the circuit board 98 is mounted on the banknote acceptance channel 48 , substantially perpendicularly to the banknote path 16 , near the interface 46 with the banknote receiving portion 4 . the banknote acceptance channel 48 , and hence the banknote path 16 defined by it , pass through a complementary shaped aperture 100 in the circuit board 98 . as is best appreciated from fig6 , which shows the circuit board 98 in isolation , the aperture 100 is surrounded by six led / sensor pairs 102 , 102 a , 102 b , 104 , 104 a , 104 b of the circuit board 98 that each act across the aperture 100 , via the banknote acceptance channel 48 . the leds 102 , 102 a , 102 b and sensors 104 , 104 a , 104 b are all located on a distal surface of the circuit board 98 . to enable banknotes in the banknote path 16 to be sensed by the circuit board 98 , the banknote acceptance channel 48 provides a major portion of a respective light path between the or each led 102 , 102 a , 102 b and sensor 104 , 104 a , 104 b of each pair . the remaining portion of each respective light path comprises a transversal of at least a portion of the banknote path 16 . whilst the banknote acceptance channel 48 holds only a portion of the light paths , it can be said to define the entire light paths . four of the led / sensor pairs 102 , 104 of the circuit board are concerned with determining the validity of banknotes and are arranged to act through the banknote path 16 , across the height of the banknote channel 48 . each of these validity determining pairs 102 , 104 comprises two adjacently mounted leds 102 . to provide light paths for the four validity determining led / sensor pairs 102 , 104 , the banknote acceptance channel 48 comprises : four integral transmitting prisms 106 which respectively steer light from the leds 102 of an associated validity determining pair 102 , 104 on the circuit board 98 , through the first major wall 48 a of the banknote acceptance channel 48 , into the banknote path 16 ; and four integral receiving prisms 108 , which are oppositely aligned to the transmitting prisms 106 across the banknote path 16 , and steer any light from the leds that is transmitted in use through a banknote in the banknote path 16 via the second major wall 48 c of the banknote acceptance channel 48 , to the sensors 104 of the validity determining pairs 102 , 104 . at an interface of the integral transmitting prisms 106 from the leds , a collecting lens is provided for collecting the light generated by a respective led . similarly , at an interface surface of the receiving prisms 108 with the sensors , a focussing lens is provided for focussing light onto a corresponding sensor . the circuit board 98 can determine the validity of banknotes in the banknote path 16 by measuring and analysing , in conventional fashion , the light received by the sensors 104 of the four validity determining led / sensor pairs 102 , 104 . a fifth led / sensor pair 102 a , 104 a is also arranged to act across the height of the banknote channel 48 and detects the insertion of banknotes into the validator 2 . the light path for the fifth led / sensor pair 102 a , 104 a , which comprises only a single led , is provided by the light guide 56 . the light guide 56 is integral with the banknote acceptance channel 48 and extends , via slits 94 , 96 in the circuit board 98 , into the cut outs 54 of the banknote receiving portion 4 , beyond the pair of wheels 40 , 42 of the receiving portion 4 , as discussed above . the light guide 56 comprises elongate transmitting and receiving arms 110 , 112 that extend proximally , in alignment with each other from outer surfaces of the first and second major walls 48 a , 48 c of the banknote acceptance channel 48 respectively , on either side of the banknote path 16 . during sensing , light travels from the fifth led / sensor pair 102 a , via an input prism , into the transmitting arm 110 . at a proximal end of the transmitting arm 110 , the light is deflected across the banknote path 16 and into the corresponding receiving arm 112 . here the light is deflected distally towards an output prism , which steers it to the sensor 104 a of the fifth led / sensor pair 102 a , 104 a . the circuit board 98 can determine whether or not a banknote has been inserted into the banknote path 16 by measuring and analysing in conventional fashion the light received by the sensor 104 a of the fifth led / sensor pair . the sixth led / sensor pair 102 b , 104 b acts to enhance the security of the banknote validator 2 and is arranged to act across the width of the banknote channel 48 . whilst the leds of the five previously described led / sensor pairs 102 , 102 a , 104 , 14 a face distally and require prisms to divert their emitted light into the banknote path 16 , the single led 104 b of the sixth sensor pair 102 b , 104 b is mounted orthogonally to the circuit board 98 and emits light directly into the first lateral wall 48 b of the banknote acceptance channel 48 . thus , to provide a light path for the sixth pair 102 b , 104 b , the acceptance channel 48 comprises an integral condensing lens in its first lateral wall 48 b , and a receiving prism in the second lateral wall 48 d to divert transmitted light to the distally facing sensor 104 b of the pair . the circuit board 98 can help to determine whether or not a fraudster is attempting to defraud the validator by measuring and analysing in conventional fashion the light received by the sensor 104 b of the sixth led / sensor pair . in summary , the banknote acceptance channel 48 , which surrounds and defines the banknote path 16 longitudinally , acts as a single optical element that provides all the necessary light paths for the sensing functions of the validator 2 . the banknote acceptance channel 48 is fabricated as a single moulded component having many integrated formations which carry out different functions . providing these functions in a single component vastly decreases costs over multicomponent solutions . whilst banknotes entering the banknote validator are initially conveyed by the pair of wheels 40 , 42 of the banknote receiving section 4 , the banknote acceptance section comprises two pairs of wheels 80 , 82 , 84 , 86 for conveyance further downstream , as illustrated in fig4 . the two pairs of wheels 80 , 82 , 84 , 86 of the banknote acceptance portion 6 are identical in structure to the pair of wheels 40 , 42 of the banknote receiving portion 4 . they are mounted adjacent to each other , and access the banknote path 16 in the banknote acceptance portion 6 , via the apertures 90 , to grip and transport banknotes . each of the two pairs of wheels 80 , 82 , 84 , 86 comprises a driven wheel 80 , 84 and an idler wheel 82 , 86 which is spring biased against the driven wheel . the driven wheels 80 , 84 are mounted in parallel on an axle 114 forming part of the drive mechanism 88 . the drive mechanism 88 additionally comprises a drive motor 116 , mounted on the proximal side of the rear plate 66 , and a system of cogs 118 operatively connecting the motor 16 and the axle 114 . as discussed above , the banknote receiving portion 4 and the banknote acceptance portion 6 are removable pivoted with respect to each other via two hinges 8 formed by bearings 33 on the receiving portion 4 and posts 72 on the acceptance portion 6 . thus the receiving portion 4 and the acceptance portion 6 may be : completely separated from each other as shown in fig3 and fig4 , or brought into a pivoted open position as shown in fig1 and fig2 , or brought into a pivoted closed position as shown in fig7 a to 7 c . in the closed position of fig7 a to 7 c , the banknote receiving portion 4 and the banknote acceptance portion 6 engage . specifically , the hinges 8 hold the portions 4 , 6 together at the third side 2 c of the validator 2 whilst , at the first side 2 a of the validator 2 , the clip 30 of the case 62 engages the slit 28 of the bezel 10 in a snap fit . at the second and fourth sides 2 b , 2 d the raised flaps 34 , 36 of the receiving portion 4 surround the second and fourth rearward side walls 64 b , 64 d of the acceptance portion 6 . the flaps 34 , 36 are located with the help of the ridges 74 , the internal location projections 37 and the indentations 78 . thus , in summary , the bezel 10 and the case 62 combine to form an enclosed chamber for the internal components of the validator 2 in the pivoted closed position . there is further , internal engagement between the banknote receiving portion 4 and the banknote acceptance portion 6 in the pivotally closed position . the banknote receiving channel 38 and the banknote acceptance channel 48 engage via the jagged ( toothed ) edges 50 , 52 at the interface 46 , rendering the banknote path 16 continuous from the receiving slot 14 to the acceptance slot 70 . also by means of this agreement a continuous banknote path defining tube is formed from input to output slot of the validator , with no longitudinal joining seam and therefore this greatly reduces the opportunity for banknote jamming to occur . further , the light guide 56 and its arms 110 , 112 engage with the banknote receiving channel 38 , whilst the second cog 60 of the transmission 44 engages with the system of cogs 118 of the drive mechanism 88 to establish an operative connection between the motor 116 and the driven wheel 40 of the receiving portion 4 . once the banknote receiving portion 4 and the banknote acceptance portion 6 are in full engagement in the closed position , the validator 2 can perform its task of validating banknotes . when a banknote is inserted into the banknote receiving slot 14 , the light circuit in the light guide 56 is interrupted . this is detected by the fifth led / sensor pair 102 a , 104 a of the circuit board 98 and the motor 116 is powered to rotate the driven wheels 40 , 80 , 84 of the validator 2 , gripping and transporting the banknote downstream , into the banknote receiving channel 38 , along the banknote path 16 . the banknote is initially only gripped and transported by the most proximal , centrally positioned pair of wheels 40 , 42 in the banknote receiving portion 4 . by virtue of its close location to the receiving slot 14 , and with the assistance of the seamless lateral walls 38 b , 38 d of the banknote receiving channel 38 , the pair 40 , 42 acts to align the banknote correctly in the banknote path 16 before the banknote can make significant downstream progress . any misalignment of the banknote by the user is corrected by the seamless lateral walls 38 b , 38 d exerting a correcting force on the banknote and the pivoting movement of the banknote about the centrally positioned pivot wheels 40 , 42 in response . more generally , the fact that the banknote channel 38 , 48 contains no seams that are in alignment with the edges of validated banknotes in use , means that the validator 2 is less prone to jamming . this is particularly enabled by the fact that the validator 2 is split into an upstream receiving portion 4 and a downstream acceptance portion 6 , between which the lateral walls 38 b , 38 d of the banknote channel 38 , 48 comprise a seam that is misaligned with the direction of banknote travel in use . once a banknote has been correctly aligned in the banknote receiving portion 4 , it enters the banknote acceptance portion 6 where it is validated by the validation led / sensor pairs 102 , 104 of the circuit board 98 acting through the banknote acceptance channel 48 . if the banknote is authenticated , i . e . found to be valid , the motor 116 , acting via the two pairs of wheels 80 , 82 , 84 , 86 in the banknote acceptance portion 6 , continues to transport the banknote downstream and out of the acceptance slot 70 , into the secure long term store . if on the other hand the banknote is not authenticated , i . e . found to be invalid , the motor 116 is reversed and the banknote is returned , upstream , through the banknote receiving slot 14 . if an attempt is made to defraud the validator by attaching a string to a banknote , this is detected by the sixth led / sensor pair 102 b , 104 a of the circuit board . referring to fig7 b , the motor 116 of the banknote validator 2 is powered by an external power supply unit 120 which may be removably mounted on the rear plate 66 of the banknote validator . the removably mounted power supply 120 can thus be easily replaced , for example to enable the validator to work on a different voltage . the banknote acceptance portion 4 and the banknote receiving portion 6 may also be individually replaced , avoiding , for example , the expensive replacement of the entire validator 2 in classes where there is only cosmetic damage to the bezel 10 . typically the banknote validator apparatus shown will be used in a conjunction with a collector or stacker mechanism although this is not shown in the drawings for ease of reference . the apparatus can be incorporated within the collector as a combined assembly or can be positioned with respect to a collector or stacker so as to allow the valid banknotes which pass along the banknote path to leave the banknote validator to automatically pass into the collector or stacker . once in the collector or stacker the banknotes are held therein until the collector or stacker is removed by authorised personnel and then emptied and / or replaced . the above embodiment of the invention is only exemplary and it will be appreciated that many modifications are possible without departing from the scope of the invention . thus , for instance , the distribution of components between the banknote receiving portion and the banknote acceptance portion may vary . further , in an alternative embodiment , seams along the banknote path may be avoided by the provision of a single banknote channel , such as a tube , that extends seamlessly from a receiving slot to an acceptance slot .