RF Transmitter

Discussion in 'The Projects Forum' started by byawire, Jan 28, 2011.

  1. byawire

    Thread Starter New Member

    Jan 28, 2011
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    I am designing a circuit to detect when a constant feed paper roll has run out. I need 4 transmitters and sensors going to receiving location. The receiver and transmitters will be about 50 feet apart.
    I was thinking of having an LED on one side of the paper and a LDR on the otherside. When the paper runs out it will sense the light, trigger the transmitter and light a display LED on the receiver. I guess I will need either a four channel receiver or run it through a microprocessor.

    I haven't done any designing for some time so any assistance will be greatly appreciated.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What will be the distance between the 4 sensors with the transmitters?
    If the sensors are quite close to eachother you could multiplex or encode the signals to one transmitter.

    Bertus
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    There are photointerrupters made to do just that. There is a slot for the paper and an IR emitter and phototransistor.
     
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  4. gizmoman0

    New Member

    Jan 21, 2010
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    Thinking about this I think you could do this with only one receiver and 4 transmitters, all set on the same channel I believe. If you had a 4 bit encoder on each transmitter and pull a unique bit high when that ream ran out, your receiving 4 bit decoder would correspondingly pull that specific bit high. So your data for each machine would spit out in general:

    0001
    0010
    0100
    1000

    And having an led hooked to each decoder bit would let you know which machine was out. Think that would work?
     
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  5. byawire

    Thread Starter New Member

    Jan 28, 2011
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    I knew there must be an off the shelf switch for what I was wanting to do but none of my searches using photoresistor and LED came up with the correct name. This way the design and testing have been done. Much Thank this is definitely going to save a lot of setup time.

    I was leaning towards the 4 bit encoder myself. Thanks for the validation.

    Thanks for all the replies. I'll run the schematics by when I work them up, Hopefully I can still solder. Any recommendations on electronic suppliers. I ran across some small transmitters/receivers from Reynolds Electronics, does anyone have any experience with them.

    Once again thanks to everyone for responding.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    Why not 2-bit? (assuming no transmission = no problem):
    00
    01
    10
    11

    Ken
     
  7. gizmoman0

    New Member

    Jan 21, 2010
    26
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    You would have to add logic gates to the decoder output to figure it out which led to light.

    I bought an rf kit and encoder/decoder set from reynolds or rentron.com I believe and they worked fine, but might be able to find the parts a bit cheaper somewhere else
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    So your receiver has 4 independent outputs? Are the 4 transmitters coded for independent identification? Do you have a specific link?

    Ken
     
  9. gizmoman0

    New Member

    Jan 21, 2010
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    The transmitters and receiver would all be on the same channel code. The photodetector would trigger the transmit enable and send the corresponding code for that device such as 0010. Then the receiver and decoder would turn on the correct led. The only problem I could see would be if more than one ream ran out at the same time the transmitters might fight and screw up the transmission
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    What color is the paper, and what color is the core?

    It could be a basic comparator circuit based on light reflected.
     
  11. byawire

    Thread Starter New Member

    Jan 28, 2011
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  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    From how I read the 4 bit pack, it only included 1 Tx and 1 Rx. So you would need to order 3 more of These, might want to double check when ordering to be sure.

    There is the possibility of collisions/lost data if two rolls run out at the same time, how likely is that?
     
  13. byawire

    Thread Starter New Member

    Jan 28, 2011
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    I do realize I need to order a total of 4 transmitters I was just posting info on what I was planning ordering. I doubt anything will run out at exactly the same time but there is a possibility that they could run out near the same time. But we are talking minutes. I don't think lost data will be a problem with a 4bit decoder if I utilize all four outputs.
    As far as color of the paper goes, it will be either white or brown. The core are usually brown. The core shouldn't be an issue if I use a photointerupter. I'm hoping it will work correctly with both color papers. I don't think it will be an issue.
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Core color won't matter with the interrupters, an edge of the paper only needs to be guided into the slot while loading a new spool, or a "swing away" arm to flip up once paper is in place.

    The idea with the cores was an idea for "contact free", simply monitoring the light reflected by the paper spool, assuming a brown (dark) core and a light (white) paper, the out of paper condition could be signaled with a reflectance meter.

    A reflective proximity sensor could be used in close (<1") to the running paper path though, even with black paper, eliminating any problems with "threading" a photointerrupter. The only requirement would be a lack of reflectance when the paper ran out. Similar theory, different way of using it. Not as reliable as interrupters, but a bit more hands off friendly.

    I'm thinking like a lazy worker and trying to guess problems that might pop up is all.
     
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  15. byawire

    Thread Starter New Member

    Jan 28, 2011
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    I appreciate all of the input. It looks like I am going to order a few different types of sensor circuits and do a little experimentation to see what works the best. I'll post my results when I prototype it.
    It seems like you have done quite a lot more of this than I have, any recommendations on suppliers. I'm just doing searches but have no experience in recent years with anyone.
     
  16. gizmoman0

    New Member

    Jan 21, 2010
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    i bought the same from rentron but with an 8 bit encoder/decoder set. works fine
     
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