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.
Referring to
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) U1, a first normally-open switch SW1, a second normally-open switch SW2, and an n-channel transistor Q. A first terminal A1 of the first normally-open switch SW1 couples to a first input terminal IN1 of the MCU U1 and couples to a power supply Vcc via a resistor R1. A first terminal B1 of the second normally-open switch SW2 couples to a second terminal IN2 of the MCU U1 and couples to the power supply Vcc via a resistor R2. Second terminals of the first and second normally-open switches SW1 and SW2 are grounded. A base of the transistor Q connects to an output terminal OUT of the MCU U1 via a resistor R3, an emitter of the transistor Q is grounded, a collector of the transistor Q connects to the power supply Vcc via a resistor R4 and couples to a power control terminal PWR. The first and second buttons 124 and 144 (see
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 SW1 and SW2 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 SW1 and SW2 are closed. The MCU U1 detects the first and second input terminals IN1 and IN2 are at low voltage level, the output terminal OUT of the MCU U1 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 SW1 and SW2 are open. The MCU U1 detects the first and second input terminals IN1 and IN2 at high voltage level, the output terminal OUT of the MCU U1 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 U1.
The MCU U1 includes a debounce circuit connected to the first and second input terminals IN1 and IN2. The MCU U1 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.
Number | Date | Country | Kind |
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2010 1 0300422 | Jan 2010 | CN | national |