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TECHVILLA
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Light & Humidity sensors
Light dependent resistor
The LDR
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LDR
• This is a resistor whose resistance depends on the amount of light falling on it.
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LDR
• This is the circuit symbol for a diode
• Draw this symbol in your books
• The arrows represent light falling on the LDR
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LDR
• When light falls on an LDR its resistance falls rapidly.
• In low light or the dark – they act as high resistors.
• In bright light they offer very little resistance
Light level
Resistance of an LDR
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LDR
• LDR’s can be used to switch on street lights when light falls.
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Humidity sensor
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What is Relative Humidity (RH)
Measurement - Relative humidity (RH) is the amount of water vapor in the air compared with the amount of vapor needed to make the air saturated at the air's current temperature
Example: At 3 p.m. the air has 9 grams of water vapor per
cubic meter of air. We divide 9 by 30 and multiply by 100 to get a relative humidity of 30%
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Water vapor air can hold in degrees C
30 degrees 30 grams per cubic meter of air
20 degrees 17 grams per cubic meter of air
10 degrees 9 grams per cubic meter of air
.
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Interfacing with avr
