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Radio Controlled LEDS?

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by crazylegsmurphy, May 27, 2008.

  1. crazylegsmurphy

    crazylegsmurphy New Member

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    Hey Everyone,

    This is my first post on this forum, so let me start out by saying hello.

    I have this project that I have had in my head for some time, and I recently decided it was a good a time as any to see if I can get it to work, so I signed up here.

    What I would like to do is, have 3 separate LED lights which would only light up if all three are close to each other (within 2 or less feet), yet when you take all three outside of that radius, they turn off.

    The question I have is, what do you all suggest would be the simplest most power friendly way of doing such a project?

    I thought about perhaps using a very simple radio controlled idea where the signal strength would only be strong enough to work within a few feet. The problem I'm having is that I need a solution that won't let only two LED's lights work if brought together, but all three.

    If any of you have any ideas to get me started I would greatly appreciate the help. Keep in mind, I am just new to the world of electronics, but eager to put in the effort to learn.

    Thanks,

    Jeff
     
    Last edited: May 27, 2008
  2. arhi

    arhi Member

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    it can be done relatively easy with microcontroler and IR. each uC can have one IR receiver and one IR LED (change current put trough led to limit the distance). All uC's modulate IR LED on 38 or 40KHz (depending on what receiver you have) and send different ID. when device detect 2 id's present it "do whatever you want when devices are close" ...

    as you will have 3 devices sending signal modulated on same frequency, you have to make "listen then talk" protocol, so something like

    - loop waiting for the silence and receive codes while looping
    - as silence is detected, transmit your code
    - wait "random" time (where random is 1-5 ms)
    - go back to loop waiting

    you can do this with simple PIC12F508 with internal osc for example

    EDIT: the downside is that you will need "line of sight" between the devices
     
    Last edited: May 27, 2008
  3. pc88

    pc88 New Member

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  4. dave

    Dave New Member

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  5. crazylegsmurphy

    crazylegsmurphy New Member

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    Awesome! Thanks!

    arhi:

    I never even thought of doing IR, but as you mentioned the line of sight issue might make it difficult as it would need a 360 degree line of sight, as well, the LED's will probably have some kind of casing around them that would distort the IR I am assuming.

    Your other ideas make sense though, is there any way to apply those to a more passive type system such as RC, or something?

    pc88:

    Thanks! From what I can gather about that link you sent is that it's doing basically what I was thinking, only in a very (seemingly) complex way...keep in mind everything looks complex at this point to me.

    I saw on Youtube a guy who made LED's light up using a RC controller. He would press the different switches, and LED's would light up accordingly. I was thinking this same concept could be used only the transmitter would always be going and the distance would be very limited (as if you were to break off the antenna to your RC car, and then walk into range holding the forward button).

    I think you guys are both onto something, I just need this concept to be very simple, very elegant and cost hopefully under $30 per LED system.
     
  6. RGBrainbow

    RGBrainbow New Member

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    Hi,

    you could use arhi's solution, but with rfPIC12F675F instead of infrared. Have a look at ReDirect. The rfPIC controllers are well documented and relatively easy to use.

    hth
    Joachim
     
  7. crazylegsmurphy

    crazylegsmurphy New Member

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    This is great!

    Ok, so I was reading the documentation on the rfPIC12F675F and it seems like I would need 3 of those and then a flash kit to program it?

    If I'm understanding this right, the rfPIC12F675F is the basic transmitter which would send the signal out.

    Where I'm getting confused is... arhi said use a "simple PIC12F508 with internal osc"

    Is the PIC12F508 a receiver, or is it the same as the rfPIC12F675F? As well, what is an "OSC?"

    Bare with me, this is pretty technical and so I'm trying to track down background reading to make this all make sense. I am getting the basic gist of it I think, and by no means am I expecting you guys to be like, "Argh...noob..ok, this is how you build it!"...but, if you could perhaps break it down slightly for me if you have the time so I could understand exactly how this might work, I would really appreciate it.

    Jeff
     
  8. arhi

    arhi Member

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    yes
    yes

    nope, PIC12F508 is just a simple uC that you can use with IR but to receive RF signal sent using rfPIC you need receiver .. for example this one:
    http://www.electro-tech-online.com/custompdfs/2008/05/70090a.pdf

    OSC is oscillator. Some uC's have internal oscillators and some require external oscillator circuit (RC or crystal with capacitors), many give you the choice, using internal oscillator saves you 2 pin's to use for io operations.

    As for the IR idea, 360 degrees is not a problem as you can "tweak" IR led by sanding the top a bit, turning it up and adding a small alu foil conus on top to "spread the light" .. it is easier solution, but the rfPIC12F675F + rfRXD0420 is more to the point of your initial request. Now, with RF you will need to find the way to tune the output so it work only on short distance. I cannot help you there as that is not my field.

    You should also check out the Min_Mass_Wireless_Coupler link pc88 provided as that is probably cheaper and easier then rfPIC12F675F + rfRXD0420 solution, especially with "distance factor" in mind.
     
  9. crazylegsmurphy

    crazylegsmurphy New Member

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    Arhi, thanks again.

    I think you're right about the IR being an easier solution, but since the LED(s) will be confined in resin, there is almost no way I can think of to give a nice optical connection as the resin will be near opaque on the outside.

    That is why I figured radio waves would be the way to go as they won't be as limited.

    The distance seems to be the factor. All the articles I am reading are about how to boost the signal, which I don't want. I don't want these things to "see" each other 1000 feet away.

    I am reading through the Min_Mass link again, it may seem easier, but it's quite confusing when you're just starting....I'm just an Make-up FX artist, not a smart tech guy like all of you, we usually don't get this complicated, and if it does, we just glue random stuff together and hope for the best. :)

    If anyone has the time, could you break down the basics of what would be needed for that Min_Max thing? I'm trying to wrap my head around it.
     
  10. crazylegsmurphy

    crazylegsmurphy New Member

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    Hmmm,

    What I'm gathering is that this person used a microcontroller as you guys suggested. But hooked up an antenna to it (somehow).

    Does he mean the "coils" are the antenna?
     
    Last edited: May 28, 2008
  11. crazylegsmurphy

    crazylegsmurphy New Member

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    So I decided to e-mail the guy who made that Min Mass thing and based on the e-mail I got from the him, it doesn't seem like it's going to be a good solution as the distance is too great.

    With that idea gone, I started looking around the net for something else that might work.

    I came across this:

    Simple FM Transmitter

    and an even simpler one:

    Simple FM Transmitter 2

    It seems to have a range of 300 feet, which I would have to reduce a lot. I would also have to take off the mic.

    Would this idea work? Here is a quick diagram of what I am trying to do in case it's not quite clear.

    [​IMG]

    Would that simple FM transmitter above (if I simply took off the mic) send out a signal that I could tune (all three different) for a receiver to pick up?

    If so, would I have issues with things like local radio stations or anything, and how would I avoid that?

    And finally, do any of you know if a simple FM receiver that would work with this?

    I found this one: FM transistor Radio

    With that said.......(sorry for the lengthy and random post)

    I also thought about using Ultrasonic...and so I found the following.

    Ultrasonic Receiver
    [​IMG]

    Ultrasonic Transmitter
    [​IMG]

    The description said that these were used to allow a robot to move around the room by bouncing the signal off objects via the transmitter, and then the receiver "hears" them.

    Now, this seems like it may work actually if I am getting this...so correct me if I'm wrong.

    If I put a transmitter in one device, and the receiver in another, when they were brought together they would "hear" each other is that right? So instead of bouncing it off objects, I would basically be pointing them right at each other.

    Now, if that is correct, then can someone help me with the following.

    - How would I change the frequency of the different transmitters so they each gave off a unique "signature?"

    - Would the transmitter send a signal out in all directions to allow for 360 degrees?

    - Could a single receiver be used to "catch" two frequencies at one time?

    - would I attach a microcontroller to the "output" on the receiver schematic which would check for two signals, and then control the LED's?

    - Would they be able to "hear" each other through up to a half inch of resin?

    - Are there any dangers to humans or pets, and would I have issues with interference?

    - What kind of distance could I expect from these, and how could I limit/extend them to minimum 1 foot?

    - What kind of power consumption do you think these would take, and could I have them "sleep" if they can't detect the other devices and then turn on when close again?

    - what are the "+V" graphics on the diagram?

    That should just about do it for questions....sorry for all of them, but this one actually seems quite promising.

    I'm really getting quite stuck on this. I'm running out of options and this seems so simple. If anyone has any ideas please share them.

    Thanks,

    Jeff

    (again, sorry for the long post)
     
  12. blueroomelectronics

    blueroomelectronics Well-Known Member

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    Sound won't work through the 1/2" of resin. The minimal mass RF coupler is somewhat directional but will work through 1/2" of resin.

    It's also very difficult if not impossible to get RF to work with a reliable range, the antenna design will determine range and direction.
     
    Last edited: Jun 2, 2008
  13. crazylegsmurphy

    crazylegsmurphy New Member

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    hmmm,

    Then that counts out that idea....

    The guy who made that Min Mass RF coupler e-mailed me and said there is almost no way I can get the signal to reach up to 1 foot. He said it's simply not designed for that distance. Plus, as you said it's pretty directional, and these devices have to have a 360 degree line of sight.

    So I'm not sure if that idea will work either.

    IR won't work as the resin will distort the IR signal.

    So, that leaves me with AM/FM it seems.

    It seems like the only thing that has the distance, will go through resin well enough, and can be easily tuned.

    Am I correct in this thinking that this is the only solution. Is it possible to have an FM transmitter send an "ID code"? What I mean is, what if all the transmitters were on the same frequency, but they were sending information from the Microcontroller....is this possible?

    Device 1 sends (I'm Device 1) over the FM frequency. Device 2 picks it up and the microcontroller looks and says, "I see device 1, but not device 2".

    I dunno, I'm getting more and more confused.
     
    Last edited: Jun 2, 2008
  14. blueroomelectronics

    blueroomelectronics Well-Known Member

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    RF (AM or FM) antennas will be directional too, it's also going to be really tough to get a reliable 1' range in all directions. You'll need a good RF engineer to help with those problems. Do you need the range the same in all orientations?
     
  15. arhi

    arhi Member

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    I'm re reading the whole thread from the start and I do not see any way how can you do it with 3 devices with "range" relatively short to work with any radio frequency .. to tune it up to detect 30cm distant device is IMHO pretty darn hard... you would have to make some pretty accurate antenna and I believe it's just too hard.

    I still think it can be done with modulated IR. Each device can have 6 or more transmitting IR LED's (mounted around the object to cover all directions), the "shield" might diffuse the IR light but if it diffuses it evenly for all transmitters it might even be helpful. You would probably have to have more then one IR Receiver on every device too .. but, with light, you can tweak the output level so you get the reasonable accuracy for those 30cm you want to "detect". Good thing about led's is that the "cap" is waterproof so they are relatively easy to install ...

    As for the idea with the sound, I believe it is also doable but only using the same idea as with the light ... detecting "bounces" will not help you here as it is very hard to detect "how many objects are bouncing signal back" .. and I believe it will be much harder to "tune" the system with sound...

    Anyhow .. I'm pretty convinced that radio will not do the job... the only possible way of using em is to go with minimal mass and find the way to increase the reach .. (as you only need to detect presence, you do not need to send data, especially if you go with 3 different resonant frequencies)
     
  16. blueroomelectronics

    blueroomelectronics Well-Known Member

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    What sort of batteries are you going to use? What sort of battery life are you hoping for?
     
  17. crazylegsmurphy

    crazylegsmurphy New Member

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    Thanks for the replies!

    Hmmm, really? I thought it was like a radio station, or a RC car controller where it just puts out a signal in all directions like those old 1940's TV ads. graphic

    I basically need all these devices to be able to be moved towards each other from any direction (probably not so much from the bottom), but all around them and above...and only within 1 foot.

    This could be my limited knowledge talking, but it seems like people think I am trying to send a radio signal out as far as I can, then have the devices detect when they're a foot away.

    I'm more thinking....well it's like this. Say you had an RC car. Typically it can transmit the signals from the joystick for 300 feet. The receiver is just passive, and it doesn't care as long as it can get a signal.

    So, say (for some reason) you wanted your RC car to only work within 10 feet and outside of that it wouldn't move as it gets no signal. So you rip off the antenna on the transmmitter. Now, the transmitter can only send a signal 10 feet so if you drive your car outside of that radius, it won't work..but if you hold in the "go" button and walk towards it, it'll work once it has a strong signal.

    I figured apply the same thing...the factor that makes it 1 foot is that I'm limiting the initial range of the transmitter so much that beyond one foot it simply doesn't have the power.

    You bring up an interesting idea with the IR LED's in say a 360 degree pattern. I still think (and I'm just guessing here) that the resin will diffuse the light so much it won't get a signal at all. The resin will be like amber (cracks, bubbles), as well as a "shell" of semi-opaque resin.

    I'm not totally discounting your idea by any means, I'm just thinking that if IR is so dependent on light reaching the target in a consistent manner, it might be tricky.
    When I asked the maker of that Min Mass device, he said (sarcastically) that if I wanted to get a range of 1 - 2 feet though resin, that I would have to have a ferrite coil 1 - 2 feet. Plus he said it's very dependent on direction as well.

    Well, I hope this doesn't become impossible problem number 2! :D

    I am so limited by space that I have to use a fairly small battery(s). Ideally, I would like the three devices (when not close to each other) run off very low power, almost as though they're in "sleep" mode until they're brought together. Ideally this "sleep" mode would last months so if they were just sitting there, they wouldn't suck all the power.

    When they're brought together however, and up to 5 LED's are on...well...that's where I would simply say, the longer the better. I mean, it has to last a reasonable amount of time, as say a LED flashlight would (I had one that ran off 3 watch batteries that lasted like 2 years or something crazy).

    The devices won't be together for extended amounts of time, but at least 8 hours minimum would be great.

    Based on size only...I could probably fit up to:

    10 - little - 12v
    2 - 9v

    Something like that.
     
    Last edited: Jun 2, 2008
  18. Torben

    Torben Well-Known Member

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    A theoretically perfect isotropic radiator does that (Isotropic radiator - Wikipedia, the free encyclopedia ) but I don't think they can be built in practice. Antennas all have characteristic radiation patterns which are affected by the shape of the antenna and what is near them.

    The device will receive (and send) more powerfully in some directions than others, and that's very hard to get around. Also, what kind of obstacles must it deal with? i.e. does it have to detect the other device(s) through a wall? Around a hand?

    What kind of cutoff do you need? I think it will also be very hard to make a device which can accurately tell the difference between the level of a signal sent from 10" away and one sent from 14" away--especially when you start adding in directionality and possible environmental obstacles and interference.

    Every few weeks someone asks about making small devices which do something like this (trigger when one device is inside/outside a certain distance from another) and so far I haven't seen anyone come up with a reliable, working solution. (Not to be a downer or anything, and I'm certainly no RF engineer.)

    What exactly is the problem you are trying to solve with these devices? Perhaps there is another (easier) way to go about it.


    Torben
     
    Last edited: Jun 2, 2008
  19. blueroomelectronics

    blueroomelectronics Well-Known Member

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    That radio graphic is just that, a graphic. Think more like waves in a pond when you throw in a stone for a simple antenna.

    The devices will have no idea when they're a foot away, signal strength will give them an idea but the signal strength will vary depending on objects nearby. Triangulation would work but is very complex.

    Omni directional RF or IR plus LED displays will likely chew through tiny batteries very quickly. Low power design takes some skill and there are always tradeoffs.

    Your LED flashlight wasn't turned ON for two years...
     
    Last edited: Jun 2, 2008
  20. crazylegsmurphy

    crazylegsmurphy New Member

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    No real obstacles at all...I mean the person bringing them together will be holding them, but they're going to turn the devices towards each other.

    I don't think it matters really, just the closer it gets, the stronger the signal. As long as it get a strong enough signal within 1 foot to let the microcontroller turn on the LED's then that's all I care about. 1 foot isn't an exact distance...it just needs to work roughly within that.

    I'm trying to make a movie prop. I'm a special make-up FX artist and I am trying to create something that will work the way I described above.

    I just need three devices that when brought together will "see" each other and allow the Microcontroller to do fancy things with the LED's. I want to find the simplest, smallest, most cost effective way to do this.

    I have heard of 4 solutions to this...each have a pro and a con.

    - IR = Pro: Good for the distance, easy to change frequencies, simple
    Con: The resin will probably distort the signal to the point where it's useless. Direct line of sight needed (360 hard to do).

    - Ultrasonic = Pro: Works at these distances, simple
    con: Can't get through resin, hard to get it to see multiple frequencies. Directional (not 360)

    - FM/AM = Pro: Easy to adjust frequency, can get through resin.
    con: Directional (not 360)

    - Min Mass RF coupler = Pro: will go through resin, simple.
    Con: Distance too short. Directional (not 360).

    I'm basically running out of ideas at this point. Every idea I have had or had presented to me is getting shot down due to one or two factors.

    I'm getting frustrated because I see devices all the time in my life that do similar things to what I want, but it apparently doesn't translate into this project.

    If there was a more simple way to do this, I would totally do it...but I'm running out of ideas.
     
  21. arhi

    arhi Member

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    I'm not that good with RF but, tuning the output of the antenna to reach 30cm is what I was talking about ... to tune the circuit to transmit signal reachable at exactly 30cm (with let say 5cm error) is for me SciFi. To make it transmit 5m with 30cm error would be more likely. Now, there sure is a way, but I do not know it... There might be someone around who can design transmitter and receiver with that precision and I really hope someone will, as I would really like to look at the schematic :) and the calculation behind it.

    It is just an idea .. I play these days lot with IR so it came as possible solution. I have tried to send 40KHz signal trough single IR LED and detect it using IR Receiver (tuned to 40KHz) through few "obstacles"... I tried (i elcosed led in alu tube to narrow the beam so I eliminate bouncing effect and force beam trough obstacle)
    - glass of water - working
    - glass filled with ice - working
    - glass filled with glass marbles - working
    - thick green plastic bottle (Cl acid was in there before) filled with glass marbles - working
    - thick black plastic bottle (from sulphuric acid)- NOT working
    - pack of CD's - NOT working

    Anyhow, you basically have (maybe we are missing something and that something might be solution)
    - sound
    - light
    - rf

    sound and light are pretty same here, you can use them to transfer data (ID), you can relatively easy tune the receiver/transmitter so you can achieve 30cm with some acceptable margin of error and you have problem that sound need to go trough the "casing" and that light will be distorted by the "casing" ... if you have casing ready, you can make some test circuit and test how both will behave. The light is easier as you have ready "one chip" receiver that will give you digital output, for sound you need to make receiver.

    rf is a different animal, it will go trough the "casing" without problem, but it is hard to achieve resolution ... if your aim was for e.g. 10m with 1m margin of error I would suggest rf .. with 30cm and few cm margin of error, it is beyond me how one can make it (again, that does not mean anything, I never made any RF circuit in my entire life)
     

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