RF transmitted "Ringer"

[magnumcalib]

I've been around working thinking of different projects to do for fun and came upon a thought (while driving home from working "tuning in" with my radar detector). Anyone have an idea on a design for a radio transmitter that transmits a signal to a receiver in our trucks (to tell them, say, to go ahead and come in and such) that makes a buzzer go off? (much like the way a radar detector "listens" for the Doplar Radar frequency to be hit). Range would be as far as I could get (in reality a few miles would be cool but just a few hundred yards would work too, I'm not sure on the laws for home brewed designs). Any help or suggestions would be appreciated, thanks.

 

[MikeMl]

Go get some of the 450MHz FRS/GMRS walkie-talkie radios. They can be bought for peanuts. They include selective calling and paging...

 

[Sceadwian]

Mind you using FRS/GMRS walkie talkies in this method is technically illegal. Would work quiet well though.

 

[magnumcalib]

Mind you using FRS/GMRS walkie talkies in this method is technically illegal. Would work quiet well though.

Yeah, I'm trying not to break FCC laws...I've gotten in trouble before (it seems my CB radio was "assembled incorrectly" and I picked up police frequencies...) I'm thinking something along the lines of how a RC car works, remote control at the base station, and in the vehicle just a receiver like you would have on the "car" end of the RC toy, and instead of a servo and motor, a buzzer. the thing is I don't know how far I could legally make a cheap RC signal go...

 

[audioguru]

My FRS radios pickup all kinds of people talking on their FRS radios.
There are so many people on FRS radios that the advertised range occurs only on Mars.

 

[magnumcalib]

My FRS radios pickup all kinds of people talking on their FRS radios.
There are so many people on FRS radios that the advertised range occurs only on Mars.

advertised range is sales gimmick, max output is 4watts, that = ABOUT 4 miles, I've increased range through clear line of sight and exterior antenna to about 8 miles. other than that you're just getting lucky

 

[Sceadwian]

Not far enough magnum. You'd be lucky to get a few hundred yards, boosting the power is your only option and again technically illegal. What's wrong with using a regular walkie talkie and just talking to the driver? Talking over the FRS/GMRS band is perfectly legal, using it to actuate a remote control device is where it becomes technically illegal. Just set up a security code on the talkie and tie it to the vehicles power. The security codes aren't particularly effective but they keep the chatter down from other people without that security code from triggering your talkie.

 

[magnumcalib]

Not far enough magnum. You'd be lucky to get a few hundred yards, boosting the power is your only option and again technically illegal. What's wrong with using a regular walkie talkie and just talking to the driver? Talking over the FRS/GMRS band is perfectly legal, using it to actuate a remote control device is where it becomes technically illegal. Just set up a security code on the talkie and tie it to the vehicles power. The security codes aren't particularly effective but they keep the chatter down from other people without that security code from triggering your talkie.

Yeah I could, I just like the idea of having the buzzer of sorts

 

[mneary]

My FRS radios (Conair "Expedition" model FRS214HT) have a Call button that sounds a nasty chime on the receiver.

 

[BrownOut]

max output is 4watts

That sounds like alot of power. Isn't the limit much lower?

 

[magnumcalib]

That sounds like alot of power. Isn't the limit much lower?

CB/FRS max output is 4watt while GFRS is 5watt, operating on GFRS requires an FCC license though. When you think of it, it's not that much power compared to some of these other radios we use. (I know it's not much of a comparison) but when you look at the amount of power a radio tower (say...106.1, here in lansing michigan) the amount of power is so high that if you were to stand next to the antenna whilst transmitting, and you were wearing contacts, they would be almost melted to your eyes.

 

[Sceadwian]

Honestly it's not that big a deal. But you should be able to use a DTMF sender and decoder. I'm just not that familiar with the letter of the law, and what is considered 'remote control' or encrypted communication, as what the signal is used for is very important in FCC law. I think FRS/CB/GFRS is pretty well locked down to voice only, but then again all the 'security codes' are is a data sensitive squelch, it sends an identification tone out when you hit the button, if the code doesn't match the one it's set for it squelches the audio. But that's built into the device itself, and hooking up an external audio source changes things, so it's a little weird.

 

[magnumcalib]

Honestly it's not that big a deal. But you should be able to use a DTMF sender and decoder. I'm just not that familiar with the letter of the law, and what is considered 'remote control' or encrypted communication, as what the signal is used for is very important in FCC law. I think FRS/CB/GFRS is pretty well locked down to voice only, but then again all the 'security codes' are is a data sensitive squelch, it sends an identification tone out when you hit the button, if the code doesn't match the one it's set for it squelches the audio. But that's built into the device itself, and hooking up an external audio source changes things, so it's a little weird.

Got any links of where to buy or links of how to build the DTMF set up? all this "device" will do is send a signal, like a garage door opener, and trigger the buzzer on the trucker end, just like a remote on off button, no buttons to make it code. So I would think it wouldn't be illegal, no codes (say like a computer) no voice transmission, just a signal that is "open gate"

 

[Sceadwian]

Umm, just one place off the top of my head. MPJA.com sells kits that will energize a small relay (fine for a light bulb or what not) when the presence of a programmable DTMF tone is recevied. There are DTMF encoder/decoder chips out there galore, but those simple little 'toy' kits work great for something like that, no muss no fuss just follow some basic instructions and provide it the right voltage. Turning the light on via a DTMF audio tone is the realm of 'remote control' though and that's illegal over those systems, but it's really silly rather than OMG you're gonna kill someone kind of illegal =)