LDR with Raspberry PI PICO |raspi pico LDR Sensor

Using an LDR with Raspberry Pi Pico: A Practical Guide

Light-dependent resistors (LDRs), also called photoresistors, are simple sensors whose resistance varies based on ambient light. In bright conditions, they exhibit low resistance; in darkness, their resistance increases significantly. This property makes them excellent for light-detecting projects such as automatic lighting, alarm systems, and environmental light monitoring.

What You’ll Need

Raspberry Pi Pico (W or standard)

• Raspberry Pi Pico (W or standard)

LDR sensor (raw LDR or preconfigured breakout module)

• LDR sensor (raw LDR or preconfigured breakout module)

Breadboard and jumper wires

• Breadboard and jumper wires

Optional: pull-down resistor (~10 kΩ) when using a raw LDR

• Optional: pull-down resistor (~10 kΩ) when using a raw LDR

Interfacing Basics

You can connect the LDR to the Pico in two common ways:

Raw LDR + resistor in a voltage divider configuration:

Connect one end of the LDR to 3.3 V.

• Connect one end of the LDR to 3.3 V.

Attach the other end of the LDR to both the ADC input (e.g., GPIO 26/27/28) and to ground through a resistor.

• Attach the other end of the LDR to both the ADC input (e.g., GPIO 26/27/28) and to ground through a resistor.

As the LDR’s resistance changes with light, the voltage at the divider midpoint shifts accordingly.

• As the LDR’s resistance changes with light, the voltage at the divider midpoint shifts accordingly.
• Raw LDR + resistor in a voltage divider configuration:Connect one end of the LDR to 3.3 V.Attach the other end of the LDR to both the ADC input (e.g., GPIO 26/27/28) and to ground through a resistor.As the LDR’s resistance changes with light, the voltage at the divider midpoint shifts accordingly.

LDR breakout module:

These modules often contain an LDR, resistor divider, potentiometer, and dual outputs: an analog voltage (AO) and a digital signal (DO).

• These modules often contain an LDR, resistor divider, potentiometer, and dual outputs: an analog voltage (AO) and a digital signal (DO).

You can read analog variations via AO or set a light threshold with DO and the onboard potentiometer.

• You can read analog variations via AO or set a light threshold with DO and the onboard potentiometer.
• LDR breakout module:These modules often contain an LDR, resistor divider, potentiometer, and dual outputs: an analog voltage (AO) and a digital signal (DO).You can read analog variations via AO or set a light threshold with DO and the onboard potentiometer.

Wiring Example with Raw LDR

Use this simple wiring:

3.3 V → LDR → ADC pin

• 3.3 V → LDR → ADC pin

ADC pin → 10 kΩ resistor → GND

• ADC pin → 10 kΩ resistor → GND

This classic divider enables the Pico’s ADC to convert the analog voltage into a digital reading between 0 and 65, 535 Sample MicroPython Code

Here’s a basic script for reading analog values in Thonny:

python

CopyEdit

from machine import ADC
import utime

ldr = ADC(28) # could use 26 or 27

while True:
value = ldr.read_u16() # 0–65535 scale
volts = value / 65535 * 3.3
print(f"ADC={value} Voltage={volts:.2f} V")
utime.sleep(1)

python

CopyEdit
from machine import ADC
import utime

ldr = ADC(28)  # could use 26 or 27

while True:
    value = ldr.read_u16()  # 0–65535 scale
    volts = value / 65535 * 3.3
    print(f"ADC={value}  Voltage={volts:.2f} V")
    utime.sleep(1)

This measures light intensity by printing the ADC value and calculated voltage

Using a Breakout Module (Analog & Digital)

With modules like the KY‑018, you get both settings:

AO (Analog Output): Connect to ADC to capture varying light levels.

• AO (Analog Output): Connect to ADC to capture varying light levels.

DO (Digital Output): Reads HIGH/LOW based on light threshold—adjustable via potentiometer

• DO (Digital Output): Reads HIGH/LOW based on light threshold—adjustable via potentiometer

Sample code for digital reading:

python

CopyEdit

from machine import Pin
import utime

sensor = Pin(0, Pin.IN) # replace with correct GPIO

while True:
state = sensor.value()
print("Bright" if state == 0 else "Dark")
utime.sleep(1)

python

CopyEdit
from machine import Pin
import utime

sensor = Pin(0, Pin.IN)  # replace with correct GPIO

while True:
    state = sensor.value()
    print("Bright" if state == 0 else "Dark")
    utime.sleep(1)

Advanced Applications

You can extend this basic setup to build real-world projects:

Automatic night lamps: Use the digital output to trigger LEDs or relay controls

• Automatic night lamps: Use the digital output to trigger LEDs or relay controls

Light meter: Continuously monitor light and log or graph values over time

• Light meter: Continuously monitor light and log or graph values over time

Solar trackers or intelligent curtains: Use threshold-based or analog readings to automate hardware movements.

• Solar trackers or intelligent curtains: Use threshold-based or analog readings to automate hardware movements.

Practical Considerations

Calibration: Ambient light responses differ between LDR units, so calibrate thresholds or voltage readings to your environment

• Calibration: Ambient light responses differ between LDR units, so calibrate thresholds or voltage readings to your environment

Analog resolution: Pico’s ADC provides 12-bit precision (0–4095) for raw readings, which you can scale accordingly

• Analog resolution: Pico’s ADC provides 12-bit precision (0–4095) for raw readings, which you can scale accordingly

Component variability: Combining an LDR with a resistor and voltage divider simplifies calibration and improves measurement consistency

• Component variability: Combining an LDR with a resistor and voltage divider simplifies calibration and improves measurement consistency