> For the complete documentation index, see [llms.txt](https://marlborough-college.gitbook.io/attic-lab/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://marlborough-college.gitbook.io/attic-lab/pi-pico-circuitpython/4.-sensors.md).

# 4. Sensors

There are a huge number of sensors available to us. Here we will learn about PIR motion detectors and an I2C environmental sensor

#### **Environmental Sensors**

1. **Temperature and Humidity:**
   * DHT11/DHT22 (Digital, GPIO)
   * AM2302 (I2C)
   * SHT31 (I2C)
   * BME280 (I2C/SPI - also measures pressure)
2. **Barometric Pressure:**
   * BMP180 (I2C)
   * BMP388 (I2C/SPI)
3. **Air Quality:**
   * MQ-series gas sensors (Analog: MQ-2, MQ-135, etc.)
   * CCS811 (I2C - VOC and eCO2)
   * SGP30 (I2C - VOC and CO2)
4. **Light and UV:**
   * TSL2561/TSL2591 (I2C - light intensity)
   * VEML6070 (I2C - UV index)
   * BH1750 (I2C - ambient light)
5. **Sound:**
   * KY-038 (Analog/Digital - microphone)
   * MAX4466/MAX9814 (Analog - microphone)

***

#### **Motion and Position Sensors**

1. **Accelerometer and Gyroscope:**
   * MPU6050 (I2C - 6-axis accelerometer/gyroscope)
   * LSM6DS3 (I2C/SPI - 6-axis IMU)
2. **Magnetometer:**
   * HMC5883L (I2C)
3. **Inertial Measurement Units (IMU):**
   * MPU9250 (I2C - 9-axis IMU)
   * BNO055 (I2C - integrated IMU with onboard processing)
4. **Distance and Proximity:**
   * HC-SR04 (Digital, GPIO - ultrasonic)
   * VL53L0X (I2C - laser time-of-flight)
5. **Tilt and Vibration:**
   * SW-520D (Digital - tilt sensor)
   * Piezo vibration sensors (Analog)

***

#### **Electrical and Magnetic Sensors**

1. **Current and Voltage:**
   * INA219 (I2C - voltage and current monitoring)
   * ACS712 (Analog - current sensing)
2. **Magnetic Field:**
   * A3144 (Digital - Hall effect)

***

#### **Health and Biometrics Sensors**

1. **Pulse and Heart Rate:**
   * MAX30102/MAX30100 (I2C - pulse oximeter and heart rate)
2. **Temperature:**
   * MLX90614 (I2C - infrared thermopile for contactless temperature)

***

#### **Image and Optical Sensors**

1. **Cameras:**
   * OV7670 (SPI - low-resolution image capture)
2. **Color Sensors:**
   * TCS34725 (I2C - RGB color sensing)

***

#### **Touch and Gesture Sensors**

1. **Touch:**
   * TTP223 (Digital - capacitive touch sensor)
2. **Gesture:**
   * APDS-9960 (I2C - gesture recognition)

***

#### **Specialized Sensors**

1. **GPS:**
   * NEO-6M (UART - GPS module)
2. **RFID:**
   * RC522 (SPI - RFID reader)
3. **Soil Moisture:**
   * Soil moisture sensors (Analog)
4. **Water Level/Leak Detection:**
   * YL-69 (Analog - water level)

## PIR Sensor

A Passive Infra Red sensor senses changes in heat and are often found in alarm systems

<figure><img src="https://683661518-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LoUl0bEh9qy_wuo9uJ4%2Fuploads%2F31MNNFPPxeY43koTgRnG%2Fimage.png?alt=media&amp;token=10532914-170c-43a3-86af-5fd6b087ef63" alt="" width="188"><figcaption></figcaption></figure>

<figure><img src="https://683661518-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LoUl0bEh9qy_wuo9uJ4%2Fuploads%2FT66xxaCBCNA3KOOcTUr3%2Fimage.png?alt=media&amp;token=9594d603-077e-4fc9-90fe-a249d2eb1c58" alt=""><figcaption></figcaption></figure>

Here we will activate a buzzer when motion is detected

<figure><img src="https://683661518-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LoUl0bEh9qy_wuo9uJ4%2Fuploads%2FfWddtdJRj0KaKyusdwBL%2Fimage.png?alt=media&amp;token=d4ec9486-3168-4885-a18c-b6e2bf8d7f7b" alt=""><figcaption></figcaption></figure>

```python
import board
import digitalio
import pwmio

# Setup digital input for PIR sensor:
pir = digitalio.DigitalInOut(board.GP16)
pir.direction = digitalio.Direction.INPUT

buzzer = pwmio.PWMOut(board.GP14, variable_frequency=True)
OFF = 0
ON = 2**15 #Sets the Duty Cycle

# Main loop that will run forever:
old_value = pir.value
while True:
    pir_value = pir.value
    if pir_value == True:
        # PIR is detecting movement! Turn on Buzzer.
        buzzer.frequency = 440
        buzzer.duty_cycle = ON
        
        
        # Check if this is the first time movement was
        # detected and print a message!
        if not old_value:
            print('Motion detected!')
    else:
        # PIR is not detecting movement. Turn off Buzzer.
        buzzer.duty_cycle = OFF
        # Again check if this is the first time movement
        # stopped and print a message.
        if old_value:
            print('Motion ended!')
            
    old_value = pir_value
    
'''CHALLENGES:
1. Can you turn on a red led when motion is detected

2. Can you get the buzzer to alternate between two different frequencies

'''
```

## AHT 20 Environmental Sensor

The AHT 20 sensor detected temperature and humidity

<figure><img src="https://683661518-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LoUl0bEh9qy_wuo9uJ4%2Fuploads%2FLxbkRfYelRpEXfgiF73D%2Fimage.png?alt=media&amp;token=bf0952f6-45b3-484f-98ec-c525d17bd7b0" alt=""><figcaption></figcaption></figure>

<figure><img src="https://683661518-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-LoUl0bEh9qy_wuo9uJ4%2Fuploads%2FozcRthtvFhIlLvn9LgYc%2Fimage.png?alt=media&amp;token=666fc1a9-e7b7-4f4d-9c4b-a7927c11e76a" alt=""><figcaption></figcaption></figure>

```python
#import libraries
import time
import board, busio
import adafruit_ahtx0

# Setup
i2c = busio.I2C(board.GP17, board.GP16) #SCL, SDA
sensor = adafruit_ahtx0.AHTx0(i2c)

#Loop
while True:
    print("\nTemperature: %0.1f C" % sensor.temperature)
    print("Humidity: %0.1f %%" % sensor.relative_humidity)
    time.sleep(2)
    
'''
Challenge: Can you turn the temperature sensor into a touch sensor that
turns on an led when you put your finger on it?

'''

```

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