Wireless IR Headphone Transmitter

The transmitter for the wireless headphones is built around a CD4046 CMOS phase-locked loop, coupled with a driver transistor, and a pair of infrared LEDs. Although the CD4046 is comprised of two phase comparators, a voltage-controlled oscillator (or VCO), a source follower, and a zener reference, only its VCO is used in this application.

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Wireless IR Headphone Receiver

IR detector diode D1 intercepts the IR signal at around 40 kHz and feeds it from U1, a high-gain preamp, to PLL, U2, a 4046 configured to serve as an FM detector. U3 is an audio amplifier that feeds a pair of headphones or a speaker.

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Remote Loudspeaker Via IR Link

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IR Pulse to Audio Converter

If your ear is good, you can use this IR-pulse-to-audio converter to troubleshoot infrared remote-controls. It is also a good project for detecting infrared-light sources. A photo cell module detects IR radiation and drives audio IC U1. This circuit is useful for troubleshooting IR remote
controls.

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IR Type Data Link

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IR Remote Extender

This circuit can be used to operate a VCR or CD player from another room. It's really an infrared signal repeater. The signal from the remote is received and then retransmitted over wires to an infrared LED. The beam from the LED is then picked up by the receiving window on the VCR or CD player.

The visible light LED (LED1) in series with the IR unit (LED2) is used to indicate that the transmitted signal has been detected. The 100-kW trimmer potentiometer (R1) adjusts the repeater's sensitivity. The resistor that is usually found in series with the LEDs is omitted, because the voltage reading is about 1.0 Vdc as a result of the voltage drop across the lines.

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IR Reflection Proximity Switch

IR radiation from LED2 (modulated by a 1-kHz wave) is keyed by U1 , and Q1 is radiated. Reflected IR energy is picked up by Q3, and the audio signal from Q3 is amplified by Q2 and sent to the decoder. The LED1 lights to indicate presence of reflected IR. LED1 can be the input of an isolator so that a triac or SCR can be controlled.

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IR Receiver

Q3 is an IR phototransistor that responds to a modulated IR beam. Q1 amplifies the ac component of the IR beam. Q2 drives a meter as a relative indication of the strength of the light beam. A strong beam gives a lower meter reading. U1 is a tone decoder that produces a low output on pin 1 during reception for an IR beam that is modulated with the correct tone frequency, determined by R6.

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Invisible Infrared Pulsed Laser Rifle

The device generates an adjustable frequency of low to medium powered IR pulses of invisible energy and must be treated with care. The portable battery pack is stepped up to 200 to 300 volts by the inverter circuit consisting of Q1, Q2, and T1. Q1 conducts until saturated, at which time, the base no longer can sustain it in an "on" state and Q1 turns "off," causing the magnetic field in its collector winding to collapse thus producing a voltage or proper phase in the base drive winding that turns on Q2 until saturated, repeating the above sequence of events in an "on/off" action. The diodes connected at the bases provide a return path for the base drive current. The stepped up squarewave voltage on the secondary of T1 is rectified and integrated on C2.

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Infrared Wireless Speaker System

Although the IR region is free from radio interference, it is subject to interference from incandescent lamps, fluorescent lamps, stray reflections, and other sources. A simple way to overcome that problem is to create a carrier by chopping the IR radiation at a rate of 100 kHz. The audio then modulates the carrier by modulating the chopping rate. A receiver then detects the IR beam as a 100-kHz FM signal. The only disadvantage is that instead of a simple audio amplifier, a high-gain FM receiver is necessary. However, with the ICs that are now available, an FM receiver is easy to build, and contains little more circuitry than a high-gain audio amplifier.

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Infrared Transmitter

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Infrared Remote Controller

The transmitter is built around two CMOS 555 timer ICs (TLC 555s). The transmitter generates a modulated 35-kHz IR signal. The 35-kHz carrier frequency is generated by IC2, and the 1 500-Hz modulating signal is generated by IC1. The output of IC2 drives LED1 through resistor R5; that LED provides visual indication that the transmitter is working. In addition, IC2 drives transistor Q1, which drives the two infrared LEDs (LED 2 and LED 3).

To provide the high current needed to drive the two IR LEDs, capacitor C6 is precharged, the charge it contains is dumped when S1 is pressed. When S1 is not pressed, the power to the ICs is cut off. However, C6 is kept charged via R8. Then, when S1 is pressed, the current stored in C6 can be used to drive the LEDs for as much as 1/2 second. That's plenty of time for the receiver to pick up a signal.

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Infrared Remote Control Tester

Using a battery, a phototransistor and a visible-light LED, this simple circuit is a go/no go tester for IR remote control devices. The illumination of the LED indicates that Q1 is being modulated by IR energy.

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