IR Remote Interferes with IR Object Detection

Mikerocontroller

· I'm running a robot with IR LED floods for navigation.· I am also using a SONY remote to send
override commands.· How do I prevent or minimize interference from the IR remote when my program
is·processing the return signal from the IR LEDs?·

·····' for example, if I were to press a remote key while this block of code is running:
·············
·····FREQOUT LeftLed,1,38500
···· leftDetect=IN0
···· FREQOUT RightLed,1,38500
···· rightDetect=IN1

···· 'the detectors pick up the IR from the remote and go LOW.
·
· Is there a way to·filter out the remote signals from the·IR LED·signals?· I know the return pulsewidth from the LED's is of shorter duration.· Is filtering a good place to start or is there something simpler I'm overlooking?
························· THANK-YOU AGAIN

erco

Tough problem, since all of your IR receivers are on a 38 kHz carrier. Your IR LED floods are sending out a brief pulse through software, and your Sony remote is repeating a digital pulse sequence·until you release the button. Or 30 seconds, whichever comes first.

You obviously have two IR detectors, possibly three if you have one just for your Sony remote.·Easiest mod is to write your code so that you're only looking for one signal at a time. That is, poll your left & right detectors a few times for any reflected IR right after a pulsout, then stop the pulsouts and look for IR·remote codes (standard Parallax ReadIR routine) for a while, then repeat the process.

Hardware-wise, you could try reducing the intensity of your Sony remote (series resistor on your IR LED, 50-100 ohms) to stop that intense, overwhelming signal from reflecting off everything in the room. Then you'll have to aim the remote directly at your robot's IR receiver. You could try optically isolating your sensors. Put your collision sensors in forward-facing tubes painted flat black. Put your IR remote sensor facing backwards in a rearward-facing tube. All this is a balancing act of signal strength, range, and detectability.

Alternatively, you could use a 56 kHz carrier for one of your sensors. Check out http://www.pololu.com/catalog/product/837 for a compatible receiver. IF the Stamp can output a 56 kHz harmonic (not sure, ask Mike Green, PhiPi or Beau!) then use these for your collision detectors. Alternatively, you could heavily modify a Sony remote to send out those control signals on a 56 kHz carrier and use this sensor on your robot to receive the remote signals.

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·"If you build it, they will come."

Post Edited (erco) : 7/12/2008 12:03:39 AM GMT

Mike Green

Probably the only thing you could do is to read the IR detector several times over a few milliseconds. It should only be true (zero) immediately after the FREQOUT and quickly change to false (one) until the next FREQOUT. If not, the IR detector is seeing some other modulated IR source and should be ignored for a while.