| 摘要 |
A circuit tester comprises a reference voltage source, an indicator with first and second response states, an indicator driver connected to the reference voltage source, an oscillator and a probe. The oscillator's output and the probe are both connected to the indicator driver's input. The indicator driver drives the indicator in the first response state when the voltage at the input is lower than the reference voltage, and in the second response state when the voltage at the input is higher than the reference voltage. The oscillator causes the indicator driver to cycle the indicator between the first and second response states when the probe is not connected to a circuit under test.
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