A two-stage isolated DCAC conversion circuit structure, consisting of a main switch, a second switch attached to a controller, another controller for controlling, and in work mode 1 and 2, after passing through the capacitor filter the low frequency half sine wave power is stored on this capacitor. The wireless modem card can be configured to detect whether a modem interface device configured to interface the wireless modem card with a host device of a second type is communicatively coupled with the host interface. Wavelength drift of the carried frequencies of the channels in detected by comparing the three signals in an electronic combinatorial logic unit. At the close contact position, the driver bit portion of the fore end of the screw tightening mechanism is brought into contact with the screw and sucks a head portion of the screw to engage the screw. The critical orifice prevents noise generated by the pump from entering the waveguide.