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