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42 lines
1.5 KiB
Markdown
42 lines
1.5 KiB
Markdown
---
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title: Reading lightness
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---
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# #17. Reading lightness
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<div class="ui segment note">
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<span class="ui ribbon label">Note</span>
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This is a web-version of a tutorial chapter embedded right into the XOD IDE.
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To get a better learning experience we recommend to install the
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<a href="/downloads/">desktop IDE</a> or start the
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<a href="/ide/">browser-based IDE</a>, and you’ll see the same tutorial there.
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</div>
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Let’s introduce a new sensor to measure an ambient light level. A
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photoresistor (aka light dependent resistor or LDR) would do a great job of
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measuring the parameter. However, there is a small problem: we do not have a
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photoresistor node in XOD.
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Yet, we have basic nodes for working with the digital and analog ports of the
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Arduino. A photoresistor is a pretty primitive device, and all we need to do is
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read its value from the analog port on the Arduino. To do so, we will use an
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`analog-input` node.
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It is a low-level node that reads an analog port of Arduino directly and
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outputs the value measured in 0–1 range where 0 corresponds to 0 volts (value
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of 0 in the Arduino native language) and 1 corresponds to the power voltage
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(usually 5 or 3.3 volts; value of 1023 in C++).
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## Test circuit
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[↓ Download as a Fritzing project](./circuit.fzz)
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Try to create a device as shown above, cover the photoresistor with your hand,
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and watch how the brightness of the LED changes.
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[Next lesson →](../18-comparisons/)
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