KY-018 Photoresistor

int sensorPin = A5; // Declare the input pin here
 
// Serial output in 9600 baud
void setup()
{
    Serial.begin(9600);
}
 
// The program measures the current voltage value at the sensor,
// calculates from this and the known series resistance the current
// resistance value of the sensor and outputs the results to the serial output
 
void loop()
{      
        // Current voltage value is measured...
    int rawValue = analogRead(sensorPin);
        float voltage = rawValue * (5.0/1023) * 1000;
         
        float resitance = 10000 * ( voltage / ( 5000.0 - voltage) );
         
    // ... and here output to the serial interface
    Serial.print("Voltage value:"); Serial.print(voltage); Serial.print("mV");
    Serial.print(", resistance value:"); Serial.print(resitance); Serial.println("Ohm");
    Serial.println("---------------------------------------");
 
    delay(500);
}

This module contains an LDR resistor whose resistance value decreases with brighter surroundings.

This resistance can be determined using a voltage divider, where a known voltage is divided across a known (10 kΩ) and an unknown (variable) resistance. Using this measured voltage, the resistance can then be calculated - the exact calculation is included in the code examples below.

Operating voltage	3,3 V - 5 V
Fixed known resistance	10 kΩ
Dimensions	21 x 15 x 6 mm

Pin assignment

Code example Raspberry Pi

Pin assignment Raspberry Pi

Raspberry Pi	Sensor
-	Signal
3,3 V [Pin 1]	+V
GND [Pin 6]	GND

Sensor	KY-053
Signal	A0
+V	-
GND	-

Raspberry Pi	KY-053
3,3 V [Pin 1]	+V
GND [Pin 6]	GND
GPIO 3 [Pin 5]	SCL
GPIO 2 [Pin 3]	SDA

Analog sensor, therefore the following must be considered: In contrast to the Arduino, the Raspberry Pi does not have any analog inputs or there is no ADC (analog digital converter) integrated in the chip of the Raspberry Pi. This limits the Raspberry Pi, if you want to use sensors, which do not output digital values, but a continuously changing value (example: potentiometer -> different position = different voltage value).

To avoid this problem, our sensor kit X40 contains the KY-053, a module with a 16-bit ADC, which you can use on the Raspberry to expand it with 4 analog inputs. This module is connected to the Raspberry Pi via I2C, takes over the analog measurement and transfers the value digitally to the Raspberry Pi.

Thus we recommend to connect the KY-053 module with the said ADC in between for analog sensors of this set. More information can be found on the KY-053 Analog Digital Converter information page.

The program uses the corresponding ADS1x15 and I2C Python libraries from Adafruit to control the ADS1115 ADC. These have been published at the following link https://github.com/adafruit/Adafruit_CircuitPython_ADS1x15 under the MIT license. The required libraries are not included in the download package below.

Please note that you need to enable I2C on your Raspberry Pi before using this example.

#!/usr/bin/python
# coding=utf-8

import time
import board
import busio
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn
import math
# Create the I2C bus
i2c = busio.I2C(board.SCL, board.SDA)

# Create the ADC object using the I2C bus
ads = ADS.ADS1115(i2c)
voltageMax = 3.3
# Create single-ended input on channels
chan0 = AnalogIn(ads, ADS.P0)
chan1 = AnalogIn(ads, ADS.P1)
chan2 = AnalogIn(ads, ADS.P2)
chan3 = AnalogIn(ads, ADS.P3)



while True:
    resistance = chan0.voltage / (voltageMax - chan0.voltage) * 10000

    print("Voltage value: ",'%.2f' % chan0.voltage, "V, resistance: ",'%.2f' % resistance, "Ω")
    print("---------------------------------------------------")
    time.sleep(1)

Example program download

KY018-RPi.zip

To start with the command:

sudo python3 KY018-RPi.py

# Load libraries
from machine import Pin
from time import sleep
import ADS1115

# Initialization of the ADC
ADS1115.init(0x48, 1, 4, False)

# Endless loop for reading the ADC | Conversion from analog value to voltage
while True:
    Analog = ADS1115.read(0)
    Volt = ADS1115.raw_to_v(ADS1115.read(0))

    # Serial output of the calculated voltage and the measured resistance
    print("The analog value is: " + str(Analog) + " at " + str(Volt) + " V")
    print('---------------')

    sleep(1)