49 lines
2.2 KiB
Markdown
49 lines
2.2 KiB
Markdown
# TeraHz Electrical Guide
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This section briefly explains the neccessary electrical connections between the
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Raspberry Pi and the sensors you'll need to make to ensure correct and safe
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operation.
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As mentioned before, TeraHz requires 3 sensors to operate. The simpler UVA/UVB
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sensor and the ambient light analyzer connect to the Raspberry's SMBus (I2C)
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bus, while the spectrometer connects via high-speed UART.
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## PCBs vs breakout boards & jumpers
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The Raspberry Pi GPIO port includes enough power pins to require only jumper
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cables to connect the sensors to the Raspberry Pi. However, this is not a great
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idea. During development, jumper cables have repeatedly been proven to be an
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unreliable nuisance, and their absolute lack of rigidity helped me fry one of my
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development Raspberry Pis. For this reason, I wholeheartedly recommend using a
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simple PCB to route the connections from the Pi to the sensors. At this time,
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there is no official TeraHz PCB, but it shall be announced and included in the
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project when basic testing will be done.
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GPIO can be routed to the PCB with a standard old IDE disk cable, and terminated
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with another 40-pin connector at the PCB. Sensor breakouts should be mounted
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through standard 0.1" connectors, male on the sensor breakout and female on the
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PCB. A shitty add-on header and a shitty add-on header v1.69bis can't hurt, either.
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## SMBus sensors
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SMBus is a well-defined version of the well-known I2C bus, widely used
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in computer motherboards for low-band bandwidth communication with various ICs,
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especially sensors and power-supply related devices. This bus is broken out on
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the Raspberry Pi GPIO port as the "I2C1" bus (see picture).
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Pins are familiarly marked as SDA and SCL, the same as with classic I2C. They
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connect to the SDA and SCL pins on the VEML6075 and APDS-9301 sensor.
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## UART sensor
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Spectral sensor attaches through the UART port on the Raspberry pi (see picture).
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The Tx and Rx lines must cross over, connecting the sensor's Tx line to the
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computer's Rx line and vice versa.
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## Power supply
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As the sensors require only a small amount of power, they can be powered directly from the Raspberry Pi itself, leeching power from the 3.3V lines.
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## Ground
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There's not a lot to say here, connect sensor GND to Pi's GND.
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