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

 

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

 

Have a look at Dick Cappel's "Minimum Mass Wireless Coupler" and related projects:

Min_Mass_Wireless_Coupler

 

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.

 

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

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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

 

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://ww1.microchip.com/downloads/e...doc/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.

 

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.

 

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?

 

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.



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


Ultrasonic Transmitter


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)

 

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.

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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.

 

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?

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Smart Kits build Smart People
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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)

 

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

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Smart Kits build Smart People
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