Jump to content
Electronics-Lab.com Community

infrared help


Um...Me123

Recommended Posts

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.

Link to comment
Share on other sites


  • 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?
Thanks

Link to comment
Share on other sites

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:

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
  • Create New...