this invention discloses a tire - pressure monitoring device directly mounting to a tire and continuously monitors the pressure in each tire . when a tire pressure is lower than a threshold low pressure , a light - emitting device as part of the tire - pressure monitoring device is activated . a low tire - pressure warning light is turned on to provide a warning of the low tire - pressure condition . fig1 shows the structural configuration of the tire - pressure monitoring device according to an exemplary embodiment of the present invention . the tire - pressure monitoring device ( tpmd ) as disclosed has a simplified structure , easy to convenient to manufacture and assemble , can be conveniently mounted on a tire , easy to operate . furthermore , the tpmd can be manufactured and operated at a very economical cost with effective monitoring process to assure proper tire pressure is maintained in each tire . in an exemplary embodiment of the invention as shown in fig1 , the tire pressure - monitoring device includes a base assembly and an upper - cover assembly that can be screwed onto the base assembly as an assembled tire - pressure monitoring device . the base assembly includes a cylinder housing 1 for receiving and containing a tire - pressure membrane 2 securely pressed and fixed in the cylinder housing 1 by a press - down ring 3 . a receiving cup 4 extends through the central hole of the press - down ring to press and engage the tire - pressure membrane 1 when the tire pressure is lower than a threshold tire pressure . a pressure adjustment spring 5 extends to the receiving cup 4 that has a rod extends into the central hole of the pressure - adjustment spring 5 to fix the pressure - adjustment spring 5 disposed substantially perpendicularly engaged to the receiving cup 4 . the upper end of the pressure - adjustment spring 5 extends through an insulation ring 6 to engage to a pressure adjustment screw 7 . the pressure - adjustment screw 7 is provided to screw onto the insulation ring 6 to adjust the length of the tire - pressure adjustment spring 5 during a normal operation pressure . the upper cover assembly includes a transparent cover 13 for containing a printed circuit board 9 disposed on top of a battery 8 and supporting a light emitting diode 10 for emitting light when the battery 8 is in physical contact and then activates the circuit disposed on the printed circuit board 9 . a current limiting resistor 11 is formed on the pcb 9 and is connected to the led 10 and all these component are tightly sealed and housed in the transparent upper cover 13 by the use of a seal ring 12 to tightly engage to the base assembly by screwing onto the base assembly . one terminal of the led 10 is connected to the current limiting resistor 11 and another terminal is engaged to a spring - plate ( not specifically shown ). the cylinder housing 1 of the base unit includes inner screws to match the outer screws of the press - down ring 3 and the outer screws of the insulation ring 6 . when the press - down ring 3 and the insulation ring 6 are screwed onto the cylinder housing 1 , the receiving cup 4 is engaged to the pressure adjustment spring 5 , and the receiving cup 4 can be moved up or down inside the cylinder housing . the receiving cup 4 can be pushed up by the tire - pressure membrane 1 or pushed down by the pressure - adjustment spring 5 . further explanations of the functions and operation processes of the tire - pressure monitoring device are provided below . the tire - pressure monitor device with a low - pressure warning signal by using a led light emitting diode includes a base assembly and an upper cover assembly screwed together . the base assembly includes a cylinder housing 1 that has screws to screw onto a tire - pressure stem of a tire . the tire - pressure membrane 2 is tight pressed down by the press down ring 3 and is therefore engaged to the opening of the tire - pressure stem . the tire - pressure membrane 2 is therefore pushed up with a higher tire pressure and pressed down by the tire - pressure adjustment spring 5 when the tire pressure is low . the press down ring 3 has outer screws to screw onto the inner screws of the cylinder housing 1 . the insulation ring 6 surrounds the press - down ring 3 and the insulation ring 6 has outer screws to screw onto the inner screws of the cylinder housing 1 . the central space of the insulation ring 6 has a ring - shaped platform with the receiving cup 4 extends therethrough with a lower end engaged to the tire - pressure membrane 2 . the receiving cup 4 further has a rod extended out to adapt to and fix the angular orientation of the tire - pressure adjustment spring 5 to position substantially perpendicular to the receiving cup 4 . the upper end of the tire - pressure adjustment spring 4 is engaged to a spring adjustment screw 7 fitting inside the ring - shaped platform inside the insulation ring 6 . the configuration as described thus allows the receiving cup 4 to move up or down inside the surrounding structures . furthermore , the tire - pressure adjustment screw 7 is able to adjust the engagement of the receiving cup 4 to the tire pressure membrane 2 by tightening or loosing the adjustment screw 7 to the insulation ring 6 . the upper cover assembly also has a central hollow space with screws to tightly screw onto the inner screws of the cylinder housing 1 of the base assembly . the central hollow space of the upper cover assembly also contains the printed circuit board 9 with a light emitting diode ( led ) 10 and a current limiting resistor 11 connected in series . the other end of the led is connected to a conductive spring plate to engage to the battery 8 . the other end of the current limiting resistor 11 is also configured as a spring plate to engage to the inside surface of the transparent cover 13 . the transparent cover 13 has outer screws to screw onto the inner screws of the cylinder housing 1 and tightly sealed through the seal ring 12 . in the process of assembling the tire - pressure monitoring device , the battery 8 is first placed inside the transparent cover 13 and screw onto the base assembly . the insulation ring 6 and the pcb are made with insulation materials and the other components are made with conductive materials . the o - ring 14 is applied to tightly seal the tire - pressure monitoring device onto the tire - pressure stem of the tire . the assembling processes starts with a step of placing the tire - pressure membrane 2 into the cylinder housing 1 and then tightly pressing down by screwing the press down ring 3 onto the cylinder housing 1 such that the low part is leak proof . the receiving cup 4 is placed inside the press down ring 3 and the tire - pressure adjustment spring 5 is placed along the spring - fixing rod . then the insulation ring is screwed onto the cylinder housing 1 thus fixes the receiving cup securely inside the cylinder housing 1 . the tire spring adjustment screw 7 is then screwed onto the insulation ring to adjust the length of the tire - pressure of the adjustment spring 5 . in assembling the upper cover assembly , the led 10 and the current limiting resistor 11 are first placed and fixed to the pct 9 . the battery is placed inside the transparent cover 13 and then screwed onto the cylinder housing 1 to complete the assembling processes of the entire device as that shown in fig2 . the positive electrode of the battery 8 is in contact with the spring length adjustment screw 7 . the spring - length adjustment screw 7 is in contact with spring 5 and electrically connected to the receiving cup 4 . the lower end of the receiving cup is in physical contact with press down ring 3 and the screws of the press down ring 3 are in physical contact with the screws of the cylinder housing . the screws of the cylinder housing 1 is near the positive electrode of the led 10 and the negative electrode of the led 10 is in connection with the negative electrode of the battery 8 through the spring plate that engages the current limiting resistor 11 . in normal operation pressure , the tire pressure pushes up the tire - pressure membrane 2 and the tire pressure membrane further pushes up the receiving cup 4 . the connection between the receiving cup 4 and the cylinder housing 1 is broken and the power supply to the led 10 is turned off . as the tire pressure falls below a threshold pressure , the tire - pressure adjustment spring 5 press down the receiving cup 4 to come into contact with the cylinder housing 1 . the led is now connected through the receiving cup 4 and the cylinder housing 1 to the battery . the current starts to flow through a closed current loop including the led 10 and that causes the led 10 to turn on . a low - pressure warning signal is there projected from the led 10 through the transparent cover 13 to provide a warning signal of the low tire pressure condition . according to above descriptions and drawings , this invention discloses a tire pressure - monitoring device ( tpmd ) directly mounted onto an air - pumping inlet - stem on a tire . the tpmd further includes a tire - pressure engaging - membrane engaged to an air pressure through the air - pumping inlet - stem pushed from an air filled in the tire . the pressure membrane pushes up a receiving cup to break an electrical connection loop in a normal tire pressure for turning off an electric power to a light emitting diode ( led ) and a pressure - adjustment spring engaged to the receiving cup pushing down the pressure membrane for closing the electrical connection loop in a low tire pressure condition to turn on the led to emit a low pressure warning light . in an exemplary embodiment , the tpmd further includes a battery for connecting and providing electric power through the electrical connection loop to the led for emitting the low pressure warning light . in another exemplary embodiment , the tpmd further includes a transparent top cover for covering and protecting the led and for transmitting the low - pressure warning light therethrough . in another exemplary embodiment , the tpmd further includes a base cylinder housing having inner screws for screwing onto the tire - pressure inlet - stem and the base cylinder housing constituting a part of the electrical connection loop with the receiving cup encompassed therein . in another exemplary embodiment , the tpmd further includes a spring adjust screw mounted on an insulation ring and engaged to the pressure - adjustment spring for adjusting a push - down pressure against the receiving cup . in another exemplary embodiment , the tpmd further includes a - down ring for engaging to the pressure membrane and screwing onto inner screws of a base cylinder housing for pressing and maintaining the pressure membrane in a fixed position inside the base cylinder housing . in another exemplary embodiment , the insulation ring further includes outer screws for screwing on inner screws of maintaining the receiving cup inside the base cylinder housing having a fixed range of up - down movement freedom depending on a pressure changes of the tire pressure . in another exemplary embodiment , the tpmd further includes a printed circuit board for supporting circuits thereon for connecting to a battery and a current limiting resistor to function as a part of the electrical connection loop . in another exemplary embodiment , the tpmd further includes a top cover having a hollow space for containing the battery , the printed circuit board and the led in the hollow space and the top cover further having outer screws for screwing onto inner screws of a base cylinder housing for assembling and containing the tpmd inside an integrated container housing formed by the top cover and the base cylinder housing . in another exemplary embodiment , the tpmd further includes an o - ring for sealing an interface between the top cover when screwing onto the base cylinder housing . in another exemplary embodiment , the the top cover further includes a transparent cover for transmitting a low pressure warning light when the led is turned on in a low tire pressure tire condition . although the present invention has been described in terms of the presently preferred embodiment , it is to be understood that such disclosure is not to be interpreted as limiting . various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure . accordingly , it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention .