Input Devices

For the individual assignment, I designed and fabricated a custom sensor extension PCB that allows me to extend the reach of my SHT45 temperature/humidity sensors throughout the beehive. The board interfaces with the Adafruit PCA9548 I²C multiplexer, which connects to the Raspberry Pi 5.

Sensor — Adafruit SHT45 with PTFE Membrane

For the input device, I'm using the Adafruit Sensirion SHT45 precision temperature and humidity sensor with a PTFE filter membrane. I have 3 of these sensors for the Smart Beehive project — one per hive box. The PTFE membrane makes them suitable for high-humidity environments like the inside of a beehive — it protects the sensor element from water and contaminants while still allowing accurate readings.

SHT45 Specifications

• Interface: I²C (address 0x44)
• Temperature accuracy: ±0.1°C
• Humidity accuracy: ±1% RH
• PTFE membrane: Protects against water, dust, and contaminants
• Voltage: 3.3V
• Quantity: 3 (one per hive box)

Sensor Extension Board — Longer Cable Runs

I have 3 SHT45 sensors that will be placed in each hive box to monitor temperature and humidity at different levels. The problem is the longest STEMMA QT / Qwiic cable I can get from Adafruit is only 300mm — not long enough to reach from the multiplexer at the bottom of the hive up through the boxes to where the sensors need to sit.

So I designed a simple extension board with two female connectors on either end. By chaining a 300mm cable into the extension board and then another 300mm cable out the other side, I can double (or triple) the reach. The board is just a pass-through — it connects VCC, GND, SDA, and SCL straight through from one connector to the other. Simple, but it solves the cable length problem without needing to solder custom-length cables.

The extension board uses the same STEMMA QT / Qwiic connector system from Adafruit — a standardized 4-pin JST SH connector that carries I²C (SDA, SCL, 3.3V, GND). This makes the whole sensor system modular and easy to work with: sensors, multiplexer, and extension boards all click together with the same cables. No soldering, no custom wiring — just plug and go.

Designing the Board

Milling & Soldering the Extension Board

Connector Rotation Fix

After I plugged everything together for the first time, I discovered an issue — the STEMMA QT cables can only be plugged in one way (they're keyed), and both connectors on my board were facing the same direction. This meant the pin order was mirrored between the two connectors — SDA on one side was connecting to SCL on the other, and vice versa. The signal wasn't passing through correctly.

The fix was to rotate one of the connectors 180° on the board so that when a cable plugs into each side, the pins line up correctly: VCC→VCC, GND→GND, SDA→SDA, SCL→SCL. I made this change to the design, resoldered the connector, and tested again — this time it worked perfectly.

Multiplexer Wiring — Adafruit PCA9548

Each SHT45 sensor is connected to the Adafruit PCA9548 I²C multiplexer, which allows the Pi to talk to all 3 sensors (they all share the same I²C address 0x44). The multiplexer sits at address 0x70 on the I²C bus and switches between channels to read each sensor individually.

Pi GPIO	Mux Pin	Wire Color
3V3	VIN	Red
GND	GND	Black
GPIO 3 (SCL)	SCL	Yellow
GPIO 2 (SDA)	SDA	Blue

Sensor channel assignments:

• Sensor 1 → Mux Channel 0
• Sensor 2 → Mux Channel 1
• Sensor 3 → Mux Channel 2

Each sensor connects to the multiplexer via STEMMA QT cables (and extension boards where needed for longer runs). The whole chain is: Pi → Multiplexer → STEMMA QT cable → Extension board (if needed) → STEMMA QT cable → SHT45 sensor. The modularity of the STEMMA QT system makes it easy to add, remove, or reposition sensors without any rewiring.

Reading the Sensor — Python on Raspberry Pi 5

Raspberry Pi 5 as the Microcontroller

For this project, the Raspberry Pi 5 serves as the microcontroller that reads the input devices. While the Pi 5 is technically a single-board computer, it functions as a microcontroller in this context — it has GPIO pins, an I²C bus, runs embedded Python code to interface directly with hardware, and controls the sensor system in real time. The custom board I designed (the sensor extension PCB) is part of the I²C circuit that connects the sensors to the Pi's I²C bus, enabling the Pi to read the SHT45 sensors over longer cable distances than would otherwise be possible.

With the extension board in place, the full signal chain is: Raspberry Pi 5 → I²C → PCA9548 Multiplexer → STEMMA QT cable → Extension Board → STEMMA QT cable → SHT45 sensor. The Pi reads temperature and humidity data from each sensor through the multiplexer using Python and the Adafruit CircuitPython libraries.

Libraries Used

• adafruit-circuitpython-sht4x — driver for the SHT45 sensor
• adafruit-circuitpython-tca9548a — driver for the PCA9548 I²C multiplexer
• adafruit-circuitpython-busdevice — I²C bus abstraction

Installation

pip3 install adafruit-circuitpython-sht4x adafruit-circuitpython-tca9548a

Code — Reading 3 SHT45 Sensors via Multiplexer

# read_sensors.py
# Reads temperature and humidity from 3x SHT45 sensors
# connected via PCA9548 I2C multiplexer on Raspberry Pi 5

import time
import board
import adafruit_sht4x
import adafruit_tca9548a

# Initialize I2C bus and multiplexer
i2c = board.I2C()
mux = adafruit_tca9548a.TCA9548A(i2c)

# Sensor locations in the hive
sensor_labels = ["Bottom Box", "Middle Box", "Top Box"]

while True:
    print(f"--- Hive Sensor Readings ---")
    for channel in range(3):
        try:
            sensor = adafruit_sht4x.SHT4x(mux[channel])
            sensor.mode = adafruit_sht4x.Mode.NOHEAT_HIGHPRECISION
            temperature = sensor.temperature
            humidity = sensor.relative_humidity
            print(f"  {sensor_labels[channel]}: {temperature:.1f}°C  |  {humidity:.1f}% RH")
        except Exception as e:
            print(f"  {sensor_labels[channel]}: Error - {e}")
    print()
    time.sleep(5)

Example Output

--- Hive Sensor Readings ---
  Bottom Box: 33.2°C  |  58.4% RH
  Middle Box: 34.7°C  |  62.1% RH
  Top Box: 35.1°C  |  65.8% RH

Relating Measurements to Physical Properties

The SHT45 measures two physical properties:

• Temperature (°C) — The sensor contains a tiny heating element and thermistor. It measures the thermal energy of the air passing through the PTFE membrane. Inside a healthy beehive, the brood nest is maintained at approximately 34–36°C by the bees. Readings outside this range can indicate problems — too cold means the colony is struggling, too hot could mean overheating or direct sun exposure.
• Relative Humidity (% RH) — The sensor has a capacitive humidity element that changes capacitance as water vapor is absorbed. Bees maintain hive humidity around 50–70% RH. High humidity (>80%) can promote mold growth and disease, while low humidity can dry out developing brood. The PTFE membrane is critical here — it prevents liquid water and contaminants from reaching the sensor while still allowing water vapor through for accurate readings.

By placing sensors at three levels in the hive (bottom, middle, top), I can monitor the temperature and humidity gradient. Heat rises, so the top box is typically warmest. This data helps assess colony health without opening the hive and disturbing the bees.

Design Files

Sensor Extension Board:

For the week 9 group assignment, our team probed input devices' analog levels and digital signals using a multimeter and oscilloscope. Full group documentation: Charlotte Lab — Week 9 Group Assignment.

What We Did

The group assignment required us to demonstrate the use of a multimeter and an oscilloscope to probe an input device's analog and digital signals. Our team split into pairs — I worked with McKinnon and Yian on the digital signal testing portion using the Analog Discovery 2.

My Contributions — Digital Signal Testing with the Analog Discovery 2

I helped set up and test digital signals from a toggle switch using the Analog Discovery 2 (AD2) — a compact USB-powered electronics tool made by Digilent that combines an oscilloscope, logic analyzer, waveform generator, and power supply into one device.

Hardware Setup

• AD2 ground pin → connected to one of the outside pins of the toggle switch
• AD2 DIO pin 0 → connected to the middle pin of the toggle switch

When the switch is in one position, ground and DIO 0 are not connected — reads logic 0. When flipped, the pins connect — reads logic 1.

WaveForms Software — Logic Analyzer Mode

We used the Logic instrument (not the oscilloscope) because we were measuring discrete 1s and 0s. Added DIO 0 as a channel and hit Run to capture the switch toggling.

Results

The switch worked — we could clearly see the digital signal toggling between 0 and 1. We noticed flickering on the transitions (switch bounce) because the small toggle switch moved around on the breadboard, briefly losing contact.

What I Learned

• Logic analyzers vs oscilloscopes: For digital signals, a logic analyzer shows clean 1s and 0s. An oscilloscope shows the actual voltage waveform — more useful for analog or transition shapes.
• Switch bounce is real: Even a simple toggle switch doesn't produce a perfectly clean signal. You need debouncing (capacitor or software delay).
• The AD2 is powerful for its size: Oscilloscope, logic analyzer, and waveform generator in one USB device — useful for debugging I²C signals on my sensor board.
• Good connections matter: The flickering was partly due to loose breadboard connections — something I kept in mind when using STEMMA QT connectors for my SHT45 sensors.