60 lines
2.2 KiB
Markdown
60 lines
2.2 KiB
Markdown
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# Space Status Circuit
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The status of Krautspace's door is captured, displayed and broadcast into the
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internet by an Arduino, a Raspberry Pi, and some circuitry. The following
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diagram shows a detailed representation of the circuit.
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The Arduino is (and should be only) responsible for the sensor read out and the
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local status display (traffic light).
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The Raspberry Pi is (and should be only) responsible for grabbing the status
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from the Arduino and broadcasting it to the internet.
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## Sensor
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The locked-unlocked-state of the door is determined by a reed switch
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embedded in the strikeplate hole, that is triggered by a magnet glued to the
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lock's deadbolt.
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The switch is connected to the Arduino via two wires.
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## Arduino
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The system uses an Arduino Duemilanove. It monitors the state of the reed switch
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and controls three LEDs on the breadboard.
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The reed switch is connect to a 5V pin and pin D13. Note, that pin D13 also
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controls the on-board LED, so whenever the switch is in the closed state (DOES
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THIS CORRESPOND TO THE DOOR BEING IN THE CLOSED STATE?), the on-board LED is on.
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Three LEDs, green, yellow, and red, on a breadboard have their anodes connected
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to pins D10, D11, and D12 and their cathodes to GND.
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The Arduino gets its power via a USB cable from the Raspberry Pi. This gives
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them with a common ground. If this were not the case, the connection between
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their grounds via the breadboard, as it exists right now and is shown in the
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diagram, would be required.
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The logic of how the state of the reed switch is converted into the state of the
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LEDs is discussed in the documentation of the Arduino software.
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## Circuit
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The circuit uses 120Ω series resistors for the LEDs.
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The circuit also includes a voltage divider for the Raspberry Pi's connection
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to the anode of the green LED. The voltage is reduced from 5V to
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1.8kΩ/(1.8kΩ + 2.1kΩ) * 5V ~= 0.5 * 5V ~= 2.5V.
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## Raspberry Pi
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The system uses a Raspberry Pi Model 3.
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The Raspberry Pi grabs the state of the green LED from its anode on the
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breadboard. This is done via pin GPIO18.
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The logic of how this state is communicated to the internet is discussed in the
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documentation for the Raspberry Pi software.
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