I am in need of some assitance in building a simple rf device to interupt dc power when the powered unit reaches a predetemined range.
Also if this range could be adjustable that would be even better.
It would of course need a transmitter and a reciever.

I have virtualy no electronics experience to speak of. I can however read schematics and diagrams, and assemble boards. I just have no idea where to start. If anyone knows where I could get a schematic to build this device or any help at all would be greatly appreciated.
Any replies can be sent to me via email
JimmeeB@aol.com
thanks in advance
JB..

 

I need help constructing a simple rf device that will interrupt dc power at a predetermined (or preferably adjustable ) range.
I will assume this project will of course need a transmitter and reciever.
I have very very little electronics knowledge. I can however read shcematics
and assemble boards.I just have no idea where to start.
If anyone could point in the right direction to obtain such a schematic or possibly send me on via email it would be greatly appreciated. Any help or comments at all however are welcome.
thanks in advance
JimeeB

 

The construction of the device will have a lot to do with how well it performs. That is, while something like, say, an audio preamp is fairly lenient as far as how long the traces are, how things are positioned, and so on, an RF circuit is not. At RF frequencies almost everything becomes an active part of the circuit.

Also, building your own RF stuff may well require a license where you are. You need to be able to prove to yourself that when you turn the thing on, you won't be opening the neighbour's garage door or making their radios go crazy.

What kind of budget are you looking at? I'd suggest buying the RF portion and just building the rest of it. Or just buy a remote-controlled power switch at the hardware store. In a pinch you might be able to hack a cheap wireless doorbell.

Anyway, we need more information:

o What is your target budget?
o What is the actual application?
o Where are you (so we know where we might suggest you go shopping for parts)?
o What is your target range?
o What kinds of load will you need to switch?


Torben

 

These sorts of schemes are highly variable, signal strength varies far too much depending on conditions.

There are actually commercially available systems for young children where an alarm is triggered if they get too far away - but again, they aren't accurate.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

ok.
MY budget is.. well as little as possible for now.

the application is for a prototype for an idea that I have which I would rather not disclose at this time. I can tell you though that it nothing illegal or terroristic or anything of the sort. I guess you could call it a saftey device of sorts.

I am in s\w florida USA

The target range will be from 10-100 ft or somewhere in that area

The load will be 6 and 12v the amperage will vary. However I dont believe it will exceed 12a

 

Dang, I clicked on the link from the thread list and didn't see the original post which makes more sense.

Jimeeb, you may safely ignore my doorbell/remote switch comments as they make no sense in this context.


Torben

 

From what little I know of it, Nigel's right. The idea comes up on the forum every so often but as far as I know, nobody's yet figured out how to make one that's very reliable.

If you don't have any size constraints you might be able to do something with RF direction-finding and use triangulation to estimate the distance, but that has a whole slew of other problems and I doubt it's what you're looking for.

Could you use GPS for this? It would again have its own issues (like, would it work in a parkade or a shopping mall?) but for out in the open you might be able to get close enough.


Torben

 

thank you torbin and nigel.
I obviously have a bit of research to do on this.
how well do you think IR might work in this application aside from the obvious
line of site?

 

You want something to turn OFF (6V and 12V, <12A) when it gets too far (10-100 ft) from a 'host'. Is that it?

IR might work indoors, if you can tolerate interference from other IR sources.

You want to keep an automatic device from running away.. like a robot (roomba, lawn mower, beer dispenser, etc.) Or you want an electronic device (radio, television, portable audio, etc.) to be inoperable when it's away from 'home'. That type of thing?

 

mneary.
yes that is the function of the device . however it does need to work outdoors as well.
I would hate to lose my beer dispenser

 

I suppose this has to work in more than one area, right? i.e. it's not as simple as setting up a perimeter wire underground which triggers the device when it crosses it, like a shopping cart wheel lock does when you try to leave the parking lot?

I'm not sure about the IR idea. If line-of-sight is acceptable it might, but I believe that IR rangefinding has its own issues at those distances. Most of the IR rangefinders I know of seem to be for quite short range (up to a few meters at most). There are people on this board with lots more experience with them than me though--maybe they know more about it.

One page you might read for some more information: http://www.societyofrobots.com/senso...pirrange.shtml


Torben

 

You could try ultrasonics. Synchronize the two units (GPS or something). Then 'home' sends bursts at a prearranged time. The rover knows how far away he is by how late the burst is relative to the original time. Both units must always be synchronized within a few milliseconds, and if the path isn't line of sight you might get some false (longer than expected) readings.

 

Ultrasound is absorbed in air pretty well (something like 1 to 3 dB per meter) so I wonder if the receiver might not need to be very sensitive (and/or the transmitter quite powerful) to operate out to 100 feet, where the signal would be something like 30 to 90 dB down. I haven't crunched the numbers on it; just seems like something that might need to be addressed. I don't know if it would make things prohibitively difficult or not; any thoughts?


Torben