Multimeter

1. Technical Field

The present disclosure relates to multimeters.

2. Description of Related Art

A multimeter is usually powered by batteries. Users often forget to turn off the power when the multimeter is idle, which affects the battery life. Therefore, there is room for improvement in the art

Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

FIG. 1 is an isometric view of an exemplary embodiment of a multimeter.

FIG. 2 is a circuit diagram of an exemplary embodiment of a switching circuit of the multimeter of FIG. 1 .

Referring to FIGS. 1 and 2 , an exemplary embodiment of a multimeter 10 includes a mainbody 11 , two wires 13 and 15 , the two wires 13 and 15 include several leads, two probes 12 and 14 to detect electrical characteristics of electrical devices or components, and a switching circuit 20 to control the mainbody 11 to power on or off. The switching circuit 20 arranges in the mainbody 11 . Each of the wires 13 and 15 includes at least two leads.

A column-shaped mounting member 122 forms on a distal end of the wire 13 , to mount the probe 12 . A column-shaped mounting member 142 forms on a distal end of the wire 15 , to mount the probe 14 . A first button 124 forms on the mounting member 122 , and a second button 144 forms on the mounting member 142 .

The switching circuit 20 includes a micro control unit (MCU) U 1 , a first normally-open switch SW 1 , a second normally-open switch SW 2 , and an n-channel transistor Q. A first terminal A 1 of the first normally-open switch SW 1 couples to a first input terminal IN 1 of the MCU U 1 and couples to a power supply V cc via a resistor R 1 . A first terminal B 1 of the second normally-open switch SW 2 couples to a second terminal IN 2 of the MCU U 1 and couples to the power supply V cc via a resistor R 2 . Second terminals of the first and second normally-open switches SW 1 and SW 2 are grounded. A base of the transistor Q connects to an output terminal OUT of the MCU U 1 via a resistor R 3 , an emitter of the transistor Q is grounded, a collector of the transistor Q connects to the power supply V cc via a resistor R 4 and couples to a power control terminal PWR. The first and second buttons 124 and 144 (see FIG. 1 ) are respectively configured to close or open the first and second normally-open switches SW 1 and SW 2 . The first normally-open switch SW 1 is insulated from the probe 12 , the second normally-open switch SW 2 is insulated from the probe 14 . The probes 12 and 14 are respectively electrically connected to the mainbody 11 through corresponding leads of the wires 13 and 15 . The first and second normally-open switches SW 1 and SW 2 are electrically connected to the MCU U 1 via other leads of the wires 13 and 15 , respectively.

In one embodiment, the transistor Q may be replaced by other types of electronic switches, such as a metal-oxide-semiconductor field-effect transistor. The first and second normally-open switches SW 1 and SW 2 may be replaced by other types of switches, such as tactile switches.

In use, the first and second buttons 124 and 144 respectively on the probes 12 and 14 are both pressed by a user, so the first and second switches SW 1 and SW 2 are closed. The MCU U 1 detects the first and second input terminals IN 1 and IN 2 are at low voltage level, the output terminal OUT of the MCU U 1 outputs a high voltage to the base of the transistor Q. The transistor Q turns on, the collector of the transistor Q outputs a control signal at low voltage level to the power control terminal PWR to control the multimeter 10 to power on.

When the multimeter 10 is idle, the first and second buttons 124 and 144 are not pressed, the first and second normally-open switches SW 1 and SW 2 are open. The MCU U 1 detects the first and second input terminals IN 1 and IN 2 at high voltage level, the output terminal OUT of the MCU U 1 outputs a low voltage to the base of the transistor Q after a period of time T. The transistor Q turns off, the collector of the transistor Q outputs a control signal at high voltage level to the power control terminal PWR to control the multimeter 10 to power off. The period of time T may be predetermined by a program written to the MCU U 1 .

The MCU U 1 includes a debounce circuit connected to the first and second input terminals IN 1 and IN 2 . The MCU U 1 outputs a high voltage only when the voltages at the first and second input terminals both remain at high level for a predetermined time to avoid accidental malfunction.

It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, the disclosure is illustrative only, and changes may be made in details, especially in matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.