| 摘要 |
PROBLEM TO BE SOLVED: To reduce number of components, downsize a shape, downsize and lighten a display portion, and improve usability, by varying a voltage level by exchanging a plurality of direct currents with a signal-processing portion to perform changeover of lighting of a plurality of display elements with two wires. SOLUTION: A signal-processing portion 4 usually outputs a signal so that a transistor 5 is turned off and the transistor 6 is turned on. Then, both end voltages of a display changeover means 7 equal to a voltage of a first direct current power supply 1 to turn on a display element 15. Because a constant voltage diode 9 is set higher than the voltage of the first direct current power supply 1, a display lamp 8 is off. When a state varies, for example, dust is detected, the signal-processing portion 4 usually outputs a signal so that the transistor 5 is turned on and the transistor 6 is turned off. Both end voltages of the display changeover means 7 equal to a voltage of a second direct current power supply 2 and exceed a set voltage of the constant voltage diode 9 to turn on the display lamp 8.
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