com.raspoid.additionalcomponents.ir

Class IRReceiver

java.lang.Object

com.raspoid.GPIOComponent

com.raspoid.additionalcomponents.ir.IRReceiver

All Implemented Interfaces:

Component

Direct Known Subclasses:

IRReceiverOS1838B

public abstract class IRReceiver
extends GPIOComponent

IR detectors are little microchips with a photocell that are tuned to listen to infrared light.

They are almost always used for remote control detection:

• AV instruments such as Audio,TV,VCR,CD,MD,DVD,etc
• Home appliances such as Air-conditioner,Fan,etc.
• CATV set top boxes
• Multi-media Equipment

Inside the remote control is a matching IR LED, which emits IR pulses to tell the device to turn on, off, etc.

IR detectors have a demodulator inside that looks for modulated IR at 38KHz. Just shining an IR LED wont be detected, it has to be PWM blinking at 38KHz.

The PWM is a "carrier" pulsing. By PWM'ing it, we let the LED cool off half the time (reason 1). Another reason to use a PWM carrier is that the TV will only listen to certain frequencies of PWM. So a Sony remote at 37KHz wont be able to work with a JVC DVD player that only wants say 50KHz (reason 2). Finally, the most important reason is that by pulsing a carrier wave, you reduce the afects of ambient lighting (reason 3).

How to decode the signal when we don't have a $1000 oscilloscope ? The IR decoder such as the 1838B does us one favor, it 'filters out' the 38KHz signal so that we only get the big chunks of signal in the milliscond range. This is much easier for a microcontroller like the Raspberry Pi to handle. Thats what we do here.

Main source of informations: https://learn.adafruit.com/ir-sensor/ir-remote-signals.

Field Summary

Fields

Modifier and Type	Field and Description
static int	MAX_PULSE The maximum pulse we'll listen for.
static int	RESOLUTION What the timing resolution should be.

Fields inherited from class com.raspoid.GPIOComponent

gpio

Constructor Summary

Constructors

Constructor and Description
IRReceiver(GPIOPin pin) Constructor for a new infrared receiver using a specific GPIO pin.

Method Summary

Modifier and Type	Method and Description
IRSignal	decodeIRSignal(IRProtocol protocol, IRSignal signal) Returns the IRSignal from IRProtocol corresponding to the input signal, or null if the input signal has no correspondance in the given protocol.
IRSignal	detectSignal() Polls until an infrared signal is detected and then return this signal.

Methods inherited from class com.raspoid.GPIOComponent

getType

Methods inherited from class java.lang.Object

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

Field Detail

MAX_PULSE

public static final int MAX_PULSE

The maximum pulse we'll listen for. 65ms is a long time.

See Also:

Constant Field Values

RESOLUTION

public static final int RESOLUTION

What the timing resolution should be. Larger is better as it's more 'precise'. But if too large, you won't get accurate timing.

See Also:

Constant Field Values

Constructor Detail

IRReceiver

public IRReceiver(GPIOPin pin)

Constructor for a new infrared receiver using a specific GPIO pin.

Parameters:

pin - the GPIO pin to use to deal with the infrared receiver.

Method Detail

detectSignal

public IRSignal detectSignal()

Polls until an infrared signal is detected and then return this signal.

! Attention ! Polling means ~100% of CPU for 1 core.

Returns:

the IRSignal corresponding to the newly detected infrared signal.

decodeIRSignal

public IRSignal decodeIRSignal(IRProtocol protocol,
                               IRSignal signal)

Returns the IRSignal from IRProtocol corresponding to the input signal, or null if the input signal has no correspondance in the given protocol.

Parameters:

protocol - the protocol to analyze.

signal - the signal to search in the protocol.

Returns:

the IRSignal from the protocol corresponding to the input signal, or null if no correspondance for the signal in the protocol.