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Flip to reveal answersWhat does an LDR give a circuit?
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All 4 Flashcards — Input devices
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Question
What does an LDR give a circuit?
Answer
A resistance that falls as light rises — hundreds of ohms in bright light, megohms in darkness. It is not a voltage until it is placed in a divider.
Question
Why does a resistive sensor need a voltage divider?
Answer
A circuit cannot act on a resistance. In series with a fixed resistor across the supply, the sensor's changing share of the supply appears as a changing voltage at the junction.
Question
How is the fixed resistor in a sensor divider chosen?
Answer
Roughly equal to the sensor's resistance at the value to be detected, so the junction sits near mid-supply where the voltage change per unit of sensing is largest.
Question
Which input devices are digital and which analogue?
Answer
Switches are digital — on or off. LDRs, thermistors, humidity sensors and microphones are analogue, giving continuously changing values.
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