First, the easy question: If you modulate teh different pairs at different frequencies then yes, they should not interfere. There is some hand waving here about the combination of various frequencies causing sensor tripping of another pair (ie, one transmitter at frequency X and one transmitter at frequency Y may together look enough like frequency Z to cause problems with receiver Z) but it's unlikely that you'll run into such problems. Your question about making the sensing distance greater by modulating the source is good. The key here is that the signal isn't going any further, but the receiver's ability to pull a signal out of the noise becomes stronger. In other words, if you see a bunch of lights in the distance you might not know which light is your home. If you call home and have your friend turn the light on and off repeatedly then you can tell by the flashing light which one is yours. It's not an issue of being able to see it - it's an issue of being able to figure out if it's the right one. So by modulating the LED source you can ignore the sunlight, flourescent lights, street lights, and even other modulated sources (at different frequencies) and pay attention to only the signal you are interested in. -Adam On 11/28/06, alan smith wrote: > After thinking, and doing some research on this....and going back to an earlier question I had asked... > > I have a bin, where material is being collected on a random basis. They are currently using some IR tx/rx setup..not sure of the parts, but in this case...its going from 6" across the opening to about 24" across. So, problem one....is being able to detect the IR signal at a greater distance, and second is interference of nearby tx/rx pairs. > > So, it was suggested that by modulating the IR, it could increase the distance. But how come? If you drive the tx harder of course, that might do it and then being in a pulsed mode it should handle the larger current but goes back to the orignal question of given a device, if you modulate the signal....does it really increase the distance it can go? > > OK second issue that can be solve by the modulated signal is the receivers are being tripped by false singals from the other tx LED's. If I was to modulate each transmitter with different frequency square wave, then each IR detector could feed to a PIC where it could measure the incoming frequency and know which device was being tripped. > > Sound reasonable? But im still curious on the distance for modulated vs unmodulated. Or did i misunderstand the answers I got before. > > > --------------------------------- > Want to start your own business? Learn how on Yahoo! Small Business. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Moving in southeast Michigan? Buy my house: http://ubasics.com/house/ Interested in electronics? Check out the projects at http://ubasics.com Building your own house? Check out http://ubasics.com/home/ -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist