Yes, the receiving LED will sense the signal from both sources. Generally when one talks about modulating the transmitter, one assumes the receiver is properly filtered and amplified. In your case the PIC would have to do the filtering. The signal received by one sensor will be the sum of the two transmitters. If you then perform a digital filter on the signal you should be able to pick out whether you are sensing one, the other, or both. If you can control the transmissions more directly, though, then you can simply light one LED up, detect it, then turn it off and light another LED up. Do this quickly enough, perform a little averaging over time to prevent false sensing, and you'll end up with the same effective result. If you are doing this all in the PIC then this is easier than performing the real filtering and signal detection inside the PIC. -Adam On 11/28/06, alan smith wrote: > Adam > > Thanks for the reponse (and ignore my other post of this morning...I usually see my posts so wonder why I didnt see this one? oh well...) > > So, to follow up, if I have two transmitters sitting across from two receivers, with about 2" seperation on the pcb for them, if I modulate one with a 40KHz burst, and the other with a 35KHz burst, both at the same time, given the fact that each receiving LED can 'see' both transmitters.....isnt the output going to be some combination of both 40 and 35? I'm thinking I need to stagger the bursts such that the adjacent transmitters will be off and thus I can look at only single receiver and feed that into a PIC to look for the square wave of whatever frequency is of interest. > > "M. Adam Davis" wrote: > 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 > > > > --------------------------------- > 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