the present invention provides a design to permit easy assembly of a mobile device with a digital camera capable of manually zooming and focusing during an image capturing process . fig1 shows a mobile device of a preferred embodiment of the present invention . the mobile device 1 includes a housing 11 and a ring 13 . in the embodiment , the mobile device 1 can be a bar - type mobile phone . the housing 11 may be an upper cover of the mobile device 1 , and the ring 13 is attached to the upper cover of the mobile device 1 . in other embodiments , the ring 13 may be disposed on a bottom cover of a mobile device . the present invention is not limited in bar - type phones , but also may be utilized in folding - type phones , sliding - cover phones , smart phones , pdas , or other mobile devices . a driving portion 131 is formed on the surface of the ring 13 , which enables a user to control a zooming - in and zooming - out function . the driving portion 131 is used to drive the ring 13 and is not limited in a specific form . for instance , the driving portion 131 can be a bulge with a regular or triangular shape . in other embodiments , the driving portion 131 may be received in a recess of the ring 13 so that a user may drive the ring 13 by the recess . fig2 shows an exploded view of the mobile device . the mobile device includes the ring 13 , the housing 11 , and the digital camera module 14 . the housing has a through hole 111 , wherein openings 1114 , 1115 , 1116 are formed around the through hole 111 and respectively correspond to protruding portions 1111 , 1112 , 1113 . a first side 1301 of the ring 13 has the driving portion 131 thereon , and a second side 1302 of the ring 13 has an extended portion 132 , and bumps 133 , 134 . in the present embodiment , the first side 1301 of the ring 13 is defined as an upper side , and the second side 1302 of the ring 13 is defined as a bottom side . in addition , the extended portion 132 further forms a hole 1321 . the digital camera module 14 includes an arm 141 and a lens 142 , wherein the arm 141 includes a short pillar 1411 corresponding to the through hole 1321 of the extended portion 132 of the ring 13 . in addition , the arm 14 is interacted with the lens 142 . when the short pillar 1411 is engaged with the through hole 1321 of the extended portion 132 of the ring 13 , the extended portion 132 is utilized to control the motion of the arm 141 for controlling the zooming function of the digital camera 14 . for instance , when the arm 141 is rotated from a first position a to a second position b , a focus of the lens 142 is changed to thus execute the zooming - in function . on the other hand , when the arm 141 is rotated from the second position b to the first position a , the digital camera 14 is capable of executing the zooming - out function . according to the design provided by the present invention , the ring 13 is allowed to be directly attached to the housing 11 , as shown in fig3 . the detailed steps of assembling the ring 13 and the housing 11 are described in the following and shown in fig4 a and 4 b . fig4 a shows the ring 13 and the housing 11 before being assembled . in the first embodiment , the housing 11 has openings 1114 , 1115 , 1116 . during assembling the ring 13 and the housing 11 , the extended portion 132 passes through one of the openings 1114 , 1115 , 1116 of the through hole 111 . in the embodiment , the extended portion 132 passes through the opening 1115 , and the bumps 133 , 134 are respectively disposed in the openings 1114 and 1116 . next , as shown in fig4 b , two sides of each of the protruding portions 1111 , 1112 , 1113 corresponding to the openings 1114 , 1115 , 1116 of the through hole 111 respectively have hitches 1121 , 1122 , 1123 , 1124 , 1125 , 1126 , and a notch is defined between each pair of the hitches . for instance , a notch 1117 is formed between the hitches 1121 and 1122 of the protruding portion 1111 . similarly , the protruding portions 1112 and 1113 correspondingly have the notches 1118 and 1119 . as shown in fig4 b , the extended portion 132 crosses the hitch 1121 and enters the notch 1117 . similarly , the bumps 133 , 134 correspondingly cross the hitches 1123 , 1125 and enter the notches 1118 , 1119 , wherein the extended portion 132 and the bumps 133 , 134 are respectively disposed on the protruding potions 1111 , 1112 , 1113 . because of the hitches 1121 , 1122 , 1123 , 1124 , 1125 , 1126 , the extended portion 132 , the bumps 133 , 134 are movably disposed in the notches 1117 , 1118 , 1119 . in another embodiment , the hitches 1121 , 1123 , and 1125 have hooks to constrain the extended portion 132 and the bumps 133 , 134 moving in the notches 1117 , 1118 , and 1119 . furthermore , the ring 13 and the housing 11 are capable of being directly assembled . the notches 1117 , 1118 , 1119 support the extended portion 132 and the bumps 133 , 134 , and thus the ring 13 is attached to the housing 11 . as described above , the second side 1302 of the ring 13 of the embodiment forms the extended portion 132 and the bumps 133 , 134 corresponding to the notches 1117 , 1118 , 1119 of the through hole 1111 of the housing 11 for coupling the ring 13 to the housing 11 . alternatively , the second side 1302 of the ring 13 is not only formed an extended portion , but also formed one or more bumps depending on different angles . moreover , the shapes of the extended portion 132 and the bumps may also be modified according to different requirements . in order to sense the change of the focus of the lens , a block ( not shown ) may be disposed in the notch 1117 and the users can feel a drop height when the extended portion 132 of the ring 13 passes the block . as mentioned above , the ring is coupled with the through hole of the housing to reduce the manufacturing cost and time . although the present invention has been explained in relation to its preferred embodiment , it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed .