Um...Me123 Posted January 14, 2007 Report Share Posted January 14, 2007 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. Quote Link to comment Share on other sites More sharing options...
ante Posted January 18, 2007 Report Share Posted January 18, 2007 I don’t believe it’s possible to change the wavelength and the problem is most likely that these are to narrow banded to communicate. Try to hook up a scope to see if there are any changes in voltage at all. Quote Link to comment Share on other sites More sharing options...
Um...Me123 Posted April 9, 2007 Author Report Share Posted April 9, 2007 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?Thanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 9, 2007 Report Share Posted April 9, 2007 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: Quote Link to comment Share on other sites More sharing options...
walid Posted April 10, 2007 Report Share Posted April 10, 2007 Himodulates the beam at about 40kHzI understand how FM, AM and PM modulation takes placeIf allowed to give us an idea of IR modulationthanks Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 10, 2007 Report Share Posted April 10, 2007 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. Quote Link to comment Share on other sites More sharing options...
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