Package com.diozero.devices

Class LDR

java.lang.Object

com.diozero.api.GpioDevice

com.diozero.api.GpioInputDevice<AnalogInputEvent>

com.diozero.api.AnalogInputDevice

com.diozero.devices.LDR

All Implemented Interfaces:

InputEventListener<AnalogInputEvent>, java.io.Closeable, java.lang.AutoCloseable, java.lang.Runnable

public class LDR
extends AnalogInputDevice

Generic Photoresistor / Light-Dependent-Resistor (LDR).
Wiring:

 vRef     vLDR       GND
   |        |         |
   +---R1---+---LDR---+
 

When there is a lot of light the LDR has low resistance (vLdr ~ 0V). When it is dark the resistance increases (vLdr ~ vRef).

vLDR = vRef * (rLDR / (rLDR + R1))

Given R1 = 10,000ohm and vRef = 5v:
When dark, if rLDR == 100,000 Ohm: vLDR = 5 * (100,000 / (100,000 + 10,000)) = 4.54V
When light, if rLDR == 100 Ohm: vLDR = 5 * (100 / (100 + 10,000)) = 0.0495V

rLDR = R1 / (vRef / vLDR - 1)

Given R1 = 10,000ohm and vRef = 5v:
When dark, if vLDR=4V: rLDR = 10,000 / (5 / 4 - 1) = 40,000 Ohm
When light, if vLDR=1V: rLDR = 10,000 / (5 / 1 - 1) = 2,500 Ohm

Field Summary

Fields inherited from class com.diozero.api.GpioDevice

gpio

Constructor Summary

Constructors

Constructor	Description
LDR(int gpio, float r1)
LDR(AnalogInputDeviceFactoryInterface deviceFactory, int gpio, float r1)

Method Summary

Modifier and Type	Method	Description
float	getLdrResistance()	Read the resistance across the LDR.

Methods inherited from class com.diozero.api.AnalogInputDevice

addListener, addListener, close, disableDeviceListener, enableDeviceListener, getRange, getScaledValue, getUnscaledValue, run, valueChanged

Methods inherited from class com.diozero.api.GpioInputDevice

addListener, removeAllListeners, removeListener

Methods inherited from class com.diozero.api.GpioDevice

getGpio

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

LDR

public LDR(int gpio, float r1) throws RuntimeIOException

Parameters:

gpio - GPIO to which the LDR is connected.

r1 - Resistor between the LDR and ground.

Throws:

RuntimeIOException - If an I/O error occurred.

LDR

public LDR(AnalogInputDeviceFactoryInterface deviceFactory, int gpio, float r1) throws RuntimeIOException

Parameters:

deviceFactory - Device factory to use to construct the device.

gpio - GPIO to which the LDR is connected.

r1 - Resistor between the LDR and ground.

Throws:

RuntimeIOException - If an I/O error occurred.

Method Details

getLdrResistance

public float getLdrResistance() throws RuntimeIOException

Read the resistance across the LDR.

Returns:

Resistance (Ohms)

Throws:

RuntimeIOException - If an I/O error occurred.