Help-Custom radio control fail safe kill switch

[jetskifreestyler]

Although a pretty handy do-it yourselfer this one is over my head. I am looking to design a radio control fail safe with a range of aprx. 50 feet. I am hoping to have a transmitter that is alerted when its (hopefully) small and light weigt reciever is out of range, triggering a shut down relay of some sort located on the transmitter.

These are my primary questions:

What type of technology should I use?
I would like to use multiple units that do not interfere with each other.
Is anyone interest in being compensated for helping me with this project?

 

[KMoffett]

This would require two-way communications in some form, for a transmitting point to recognise when a receiving point no longer "hears" it. Is it possible for the transmitter to be on the "mobile" part, and the receiver to be the one that shuts down the relay? Or does the transmitter control other things on the "mobile" receiver while it's in-range?

This wouldn't happen to have anything to do with falling off a jet ski, would it????

Ken

 

[Leftyretro]

As stated the transmitter is dumb, it only sends out a signal in hope that the receiver will pick it up. Only the receiver knows if the signal is strong enough for proper reception. Now if you used transceivers at both ends then some kind of protocol could allow one to know if messages were being processed correctly.

Lefty

 

[jetskifreestyler]

Hmmm...

I was thinking that the tramsmitter uses more power and would probably be a bulkier unit so I would like that to be the part that triggers the shut down mechanism. If I am wrong about my theories please let me know. One of the two units has to be small and battery powered and the other can be larger and hard wired into 12v. Thanks for your responses.

 

[Papabravo]

Any mechanical system you come up with will be way more reliable than any two-way RF system. Aside from the power limits on unlicensed devices you may need to think through the implications of iterference or malicious mischeif. If the device needs to operate in, shal we say, a moist environment there will be additional problems.

A typical treadmill has a little plastic key that gets inserted in a slot and is attached to your waistband. If you fall the shutoff is immediate. Do you really want to get dumped and have to wait for the ski to go to the range limit of the RF system?

 

[jetskifreestyler]

Yes

Thats the idea. The conventinal system is mechanical and has a rip cord to shut down. I do freestyle and it is standard protocall to have not all or sometimes any of your limbs attached to the jet ski.

 

[RadioRon]

Papabravos point is a very important one. Interference is a big problem in simple systems and often pushes designers to more elaborate protocols just to avoid false signals. For example, it will be necessary to come up with a way that insures that several jetskiers, all using exactly the same system, can be close to each other and not suffer a fault due to inteference. Well, that is if you are making more than one. If not, then this is less of an issue. There is also the problem of multipath that could affect reliability, but perhaps the careful choice of frequencies will minimize this. Again, if you're only making one, then don't worry about this next thing, but if you want to make a product out of it, then the next big thing is that you have to work within government radio regulations which are quite restrictive. These regulations might force you into specific frequency bands, where you have to share with others and the interference they bring.

So, what kind of range are you thinking of? Trigger in, say, 30 feet?

 

[jetskifreestyler]

Range

Yes 30 to 50 foot range would be perfect and I would like to produce multiple units. Thank you guys for all your info this is definately helping. I thought that it would have been more simple but that is not going to discourage me in developing this project. I hadn't really imagined that interference would have been a problem with such a simple signal. Do you think that a high powered ignition system on the motor would cause interference problems?