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infrared help


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I bought some infrared leds and phototransistors on ebay.  Hooked them up to a microcontroller board and  put them right face to face and no sound.  I looked with a video camera and the infrared was blinking.  Tried with a sterio remote and it did beep.  I know the emmiter can do 940nm and I really don't understand this.  If the phototransistor can only do a lower ammount 800 something? will it not work?  Can I lower the wavelength of the emmitter somehow if this is the case?  I just need help in understanding infrared.  I checked the code and am pretty sure the "IF IN15 = 1" part isn't just during the off stages of the LED.

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  • 2 months later...

I went back to re-challenge these IR deals with a project that would make lights go on when you enter a room and off when you exit.  The IR leds can communicate now but for only about 4-5 inches at a 1ms on / 5ms off pulse.  (in low light conditions)  I'm just learning but I want to know how to make the IR beam work at a farther length (across a doorway)  without increasing the off time.  I have 5V from the PIC board or could get 9V from the PS (then using a transistor) if that helps.
Looking through a video camera these IR leds seem to be significantly dimmer than a remote control.  How do they make them work so far away?

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A modern IR remote control uses a high current in one or two IR LEDs and modulates the beam at about 40kHz.
The IR receiver is an infrared detector IC with a photo-diode and a high gain amplifier tuned to the 40kHz. The photo-diode has a visible light blocking cover that looks black but passes IR radiation.

Here is what is inside a modern IR detector IC:

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The IR beam is pulsed with a square-wave at about 40kHz. A logic high has the pulsed beam turned on and a logic low has the beam turned off.

The IR receiver has a narrow bandpass filter tuned to about 40kHz so continuous IR radiation or IR that is pulsed at a different frequency doesn't cause too much interference.

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