project founded by an idea

[HiTech]

Some of it is through established radio beacon points. I'm still trying to understand this project founded by an idea concept. It must involve an advanced level of transcendental medication!!

 

[evilstrike]

Lol according to the replies, im getting, it seems quite hard to accomplish. In my head though it looked simple enough hehe

the project founded by idea concept simply refers to a project that I started followed by an idea to make something and that "something" involves finding a way to measure distance between 2 hand held device from which I though could of been acheived with some type of RF, IR, Wireless or bluethooth transmiter & receiver

See the reason why I though this might not be complicated and hard to do is because I though that that is what cordless mouse & keyboard do.

The mouse sends some type of data to the receiver on relays it to the computer and makes the mouse cursor moved. I assumed that if its possible to do that then it should not be hard to do the same but instead of sending X and Y coordinates it would send distance, or time or whatever. Its just a matter on finding what data to send and what do to with the data onces its received. Because correct me if im wrong but a cordless mouse is a transmiter and the dock that is hooked to the computer via USB is the receiver. And it is not juste sending frequencies, its sending it some X and Y coordinates used for cursor positioning. Same goes for the keyboard, it sends the receiver whatever key was pressed. More technically, i think the data is sent in binary but that is not a big deal as If i were to send time, All i would need to do is convert the timestamp into binary in the same way as the keybaord and mouse does it"

What I think is that maybe I didnt explain this the right way or you are all thinking of something on a large and advanced scale.

 

[Sig239]

I'm also confused. I think what he wants are two devices that give an output when said devices are a "yet to be determined" distance or more away from each other. Does any other data need to be transmitted?
EDIT: No a mouse doesn't give x y coordinates, if it did then the pointer would go to the middle of the screen when you set the mouse down in the middle of your mouse pad. The mouse just measures the distance and direction you have slid the mouse across the pad. It uses the current location of the cursor as a point of reference.

 

[evilstrike]

Does any other data need to be transmitted?

No, all there is to be sent is data which contains a way to determine the distance that separate the two devices in a short range. I said 10meters as an example but the determined distance could be something like 10feet instead of 10meter

and it doesnt need to be measured in feet or meters in can be in anything but it has to be significant in or to be able to calculated a difference

Maybe a motion detector from an alarm system might explain this, now im not sure they work this way but if they do then it is kinda what Im trying to do

A motion detector will detect motion from inside a specifed range. If you walk outside the range, the detector will not inform the system. If you do get into its range, it will tell the system and the system will sound the alarm.

In that case the motion detector has to have some sort of way on calculating its range which can be converted to a distance. Although, im mostlikly wrong on how they work though

 

[evilstrike]

EDIT: No a mouse doesn't give x y coordinates, if it did then the pointer would go to the middle of the screen when you set the mouse down in the middle of your mouse pad. The mouse just measures the distance and direction you have slid the mouse across the pad. It uses the current location of the cursor as a point of reference.

Ok well I said X and Y cause I really didnt know what was sent but its good to know that. But what ever it is sending, it is sending data and the data is being read by the transmiter and action is being taken with the received data.

This is really what I would need execept, I would need to send something to determine how far the receiver is for the transmiter

Couldnt I just take what was said at the beginning with the clocks? What would happen if I added a clock in a mouse synced with one in the receiver. Woulndt I be able to send the timestamp of the mouse with the other data that the mouse sends to the receiver and calculate the difference?

 

[Nigel Goodwin]

Couldnt I just take what was said at the beginning with the clocks? What would happen if I added a clock in a mouse synced with one in the receiver. Woulndt I be able to send the timestamp of the mouse with the other data that the mouse sends to the receiver and calculate the difference?

How are the clocks to be synced together?, you don't seem to appreciate how small the time intervals you need to measure are? - bear in mind the radio waves are travelling at the same speed at the current in the wires of your circuit!.

 

[Hero999]

How are the clocks to be synced together?, you don't seem to appreciate how small the time intervals you need to measure are? - bear in mind the radio waves are travelling faster than the current in the wires of your circuit!.

Fixed .

 

[evilstrike]

you don't seem to appreciate how small the time intervals you need to measure are?

not sure what you mean by that...
I have no preference in time measurement, I can be in seconds, nanoseconds, picoseconds, just as long as there is a significant difference to be able to be calculated.

How are the clocks to be synced together

how about the same way you would sync a watch? It woulnt need to be exactly synced because what can be done is sync the receiver and then sync the transmiter exactly 5 seconds after. Since you would know that they are exactly 5 second appart then you would simply have to keep in mind to add or subtract the 5 second delay to the equation

 

[Sig239]

The alarm sensors you refer to don't measure range either, nor do they use any range information. They are only capable of working in a certain range. If this type of response is suitable to your application then maybe you should use something that will only transmit a certain small distance(10ft.), then just try to detect the signal. If you can detect it then it is closer than 10 ft. if not then it is farther away.

I have one of those Boe bot kits that are based on a basic stamp 2 microcontroller, and it uses the frequency response curve of a ir detector to achieve similar results. You transmit ir pulses at different frequencies. Each frequency detected represents a different distance. If this doesn't make sense to you I will explain further. It was a great discovery for me.

 

[evilstrike]

The alarm sensors you refer to don't measure range either, nor do they use any range information. They are only capable of working in a certain range. If this type of response is suitable to your application then maybe you should use something that will only transmit a certain small distance(10ft.), then just try to detect the signal. If you can detect it then it is closer than 10 ft. if not then it is farther away.

Oh then I think this is even better but how would it be done? Because motion detectors dont send a signal to a perticular device nor do they listen for a signal coming from a specific device. What I would need is for the motion detector to sound the alarm only if the transmiting device enters the detector 10feet range meaning that if the detector does not recieve a signal from the transmiting device it does nothing and when it does recieve it then it rings.

 

[Sig239]

Oh then I think this is even better but how would it be done? Because motion detectors donc send a signal to a perticual device nor do they listen for a signal coming from a specific device. What I would need is for the motion detector to to sound the alarm only if the transmiting device enters the detector 10feet range

HUH Well how do you think they work? Instead of us just bouncing around from idea to idea how about you tell us exactly what you are trying to achieve (with all the details) then we can determine how complicated it needs to be. None of us wants to reinvent the wheel or add unneeded complexities.

 

[dknguyen]

Radars and tracking devices measure the time it takes for a radar beam to echo back.

I don't know where you got the idea that motion sensors don't transmit or listen, because how else would they work? Motion sensors (which do not provide range information like radar and are also much cheaper) use the doppler effect. They send out a continuous fixed frequency wave and measure the frequency of echo. Any motion in the field that is not perfectly perpindicular to the waves (anything that is moving even slightly towards or away from the transmitter) will produce a doppler frequency shift. So if the received echo frequency is not the same on that is sent out, you can tell if something is moving towards or away (not side to side). It can only measure the velocity component parallel to the waves.

I have no preference in time measurement, I can be in seconds, nanoseconds, picoseconds, just as long as there is a significant difference to be able to be calculated.

THe units do not matter. I think you are misunderstanding. We don't mean the units used for calculation. What we mean is that the time frame of such events are in picoseconds if you use one, two, or three digit integer numbers. It doesn't matter if you calculate in seconds, milliseconds, nanoseconds, or picoseconds. What we mean is the time of flight for electromagnetic waves is on the order of picoseconds and to design/buy circuitry that can work that fast is very difficult/expensive. That IS the problem. There is no significant difference to measure. THe speed of light is 300,000,000 m/s. You want a working range of about 10m. Take out your calulator and find out how many seconds it takes light to travel 10m. Do you understand what we mean now by you not appreciating how small the time invervals involved are? Think about it, something like sound is soooo slow compared to the electronics you can totally ignore the time it takes for the circuit to work. But with electromagnetic waves, their speed rivals (usually exceeding) the speed of the electronics, so everything suddenly all the little delays in the circuit become important...a major pain in the ass.

how about the same way you would sync a watch? It woulnt need to be exactly synced because what can be done is sync the receiver and then sync the transmiter exactly 5 seconds after. Since you would know that they are exactly 5 second appart then you would simply have to keep in mind to add or subtract the 5 second delay to the equation

Keeping the tiny time differences mentioned above in mind, synching with a stopwatch watch based on your reflexes (or any conventionally found reflexes) would be useless because you have to get the clocks within picoseconds of each other. The other problem is, are they REALLY 5 seconds apart? Down to the picosecond? Or is it 5.0000006 seconds apart? Assuming you were able to synchronize something to this RIDICULOUSLY accuracy,that "tiny" 0.0000006 second (600,000 picoseconds) error will cause an error of 160m in your readings...on the transmit. On the echo it would introduce another 160m error reading. So even if you did pull off synching to this ludicrous accuracy, your error would be +/- 320m. Also, the act of merely walking by the sensor would cause enough vibrations and nudge your transmitter receiver enough to totally mess up the stopwatch synching that you took so much work to do.

 

[evilstrike]

I don't know where you got the idea that motion sensors don't transmit or listen

I didnt say that motion detectors didnt transmist or receive a signal, what I said was that it didnt transmist or receive a signal comming from a specific device. For example, the motion would not sound the alarm if you entered its range holding a divice that would say "hey I live here" and it would sound the alarm if you would enter its range without that device. That was sence in which I meant while saying they didnt transmit and receive.

I though the project was clear but I guess it is still quite unclear to many.
Here I will make it simple, You have 2 devices. Device A and Device B and Device A has a LED on it

The idea is the LED on Device A will only light up if Device B is at a certain distance or range from Device A but will stay off as long as Device B stays below the desired range or distance

Is this a better explantion?

 

[dknguyen]

If you are using only RF, the easiest way is to adjust the power of the transmitter by trial and error until you get the distant you want. It will not be an absolute hard distance threshold, but that's not really needed anyways. You only need to know "too far" or "not too far". If you try to measure and calculate the distance with RF that gets very hard.

But here is another idea that should serve you very well. Use an electromagnetic wave AND sound. Transmit both from the transmitter simultaneously. Light travels so fast that you can assume it instantly reaches the receiver. Because it is instant, the EM wave tells us when the sound was transmitted. Therefore, if you measure the time difference between the arrival of the light and sound to the receiver, you can figure out how long it took for the sound to get to the receiver. From this you can calculate how far the transmitter is away. You do not have to assume EM waves reaches the transmitter instantly (you don't even have to use EM waves, as long as you have two different waves that travel at different speeds). It just makes the calculations simpler since the travel time of EM waves is so small over these distances you can assume it is zero. And sound travels so slow compared to electronics, it is easy to measure.

Normally, IR light is used for something like this, but because there may be walls in the way (or not have line of sight between transmitter and receiver) for your application, you can use a radio wave that can pass through walls. Sound can travel around corners so having walls in the way is not a problem for sound.

Remember that it takes a lot of power to transmit sound and light so often. So, you can have your receiver (which is plugged into the wall so has lots of power) always radiate a second radio signal that turns on the EM-wave/sound transmitter when it is in range. This way, you can save battery power by stopping the transmitter from sending electromagnetic and sound waves when it is far out of range of the receiver. THe bad thing is that now the receiver AND transmitter are transceivers, rather than just a transmitter or receiver.

Lower frequency sounds are the best for this because they travel the farthest and spread the widest (high frequency sounds travel in narrow beams and travel short distances). You could make it audible but that could be annoying, especially if you nowhere near the receiver (or if you had the activation signal from the receiver, it could be annoying whenever you were near the receiver). If the distance is just 10m, you could use low utrasonic frequencies, just beyond the range of human hearing. But it might hurt dogs and other things with better hearing.

 

[evilstrike]

(I just read your original question, and were you even asking for a motion sensor? Or just for a device to wirelessly disable something when you were in the are?

No I wasnt asking about motion detector. The motion detector idea came into play when I was trying to find something that kinda did what I wanted to do. The problem I think is when I asked that I needed to calculate distance. That is because I assumed that that was the way to go, but I think the motion detector sparked a new view as to how this can be done. The goal of this is in fact to have a device to wirelessly disable something when you are in the area.

I have no preference on which kind of wireless to use which Is why I came here to try and find out what type of signal would be best for this and what I can use for this.

The problem of IR not going through walls is why I originally stated using RF as I knew RF went through walls and this project has to pass through walls.

I think what threw everyone off on this is the measuring of distance. But after reading about the motion detector I think now that detecting if a device in present in a desired range is alot easier then trying to calculate the distance separating the 2 devices.

So do you think its possible at low cost to use a motion detector to detect the presence of a perticual tagged device and take action of it sees the device?

 

[dknguyen]

I was editing my previous post when you responded. Thanks.

No, I do not think it is possible with aconventional motion detector, but there are other, potentially better ways (like the RF/sound method I just added in my previous response)

Since RF and IR both travel really fast, it is hard to use them by themselves to measure distance, whether or not they can pass through walls. But if you combine them with slow travelling sound it becomes much easier and you can use the high speed of electromagnetic waves (which both IR and RF are) you can take advantage of their high speed by assuming they reach the receiver instantly as a timing signal for when the sound was transmitted. This lets you simplify the calculations a little bit since you don't have to account for travel time of the electromagnetic wave, since it is so fast compared to sound. You can just treat the the instant you receive the EM wave as the instant the sound was transmitted.

 

[evilstrike]

ok but see I dont "need" to measure the distance. I wanted to measure the distance because I thougt that that was the only way to be able to get the LED to light up.

How do those robot lawn mower or robot vacume cleaner work? Because with those robots you can add a ground barrier. If the robot neers the barrier its turn arround. This is mostliky more what Im looking for. What type if signal is being set from the barrier to the robot for the robot to know not do go further then the barrier?

I taking for example the follow iRobot
**broken link removed**

they use a ground transmiter to tell the robot to turn arround

 

[dknguyen]

I believe those just use some kind of IR pass-through beam (or magnetic wire). They work more like borders, than for a single area. You could achieve the same thing by using passive RFID tags with detectors along each entry way into the area.

Systems like this are more for outlining areas than to figure out if something is within the area. YOu can't detect if something is within the area so much as you can detect if something is passing between the borders of the area (you cannot differentiate between passing in or out).

 

[ClydeCrashKop]

Two transmitter / receivers could do this. The stationary unit would transmit a signal and start a high speed counter. When the mobile unit detects the signal, it would answer. When the stationary unit detects the answer it would stop the counter. Now you have a number you can work with representing how long it took the signal to get from point A to point B and back.
Somewhere in cyberspace is a thread from a man wanting to plot the XY position of a go-cart on various race tracks. It required two transmitter / receiver pairs at right angles to the track. The signal that the stationary units would transmit would be the previous counter result that his computer receive also to plot coordinates.

 

[Sig239]

Incidentaly, it seems that he does not really need the actual distance or xy coordinates. He really does not know what he needs, and he won't tell us the actual situation he needs the project for, so he is not making it very easy for any one to help. He gives hypothetical situations that end up not being acurate to his actual situation. Perhaps more acurately, he is incorrectly assuming the way some things work then coming up with ideas to use them improperly. I see the creative value in doing such things, but it can be frustrating when others are trying to help. At any rate you are welcome to give it a go...lol