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From: Lizard Blizzard
Subject: Re: Single / Multitone Detector (Not DTMF)
Date: Tue, 14 Jan 2003 07:59:08 -0800
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> On Mon, 13 Jan 2003 11:12:02 -0500, Terry King
>>1: I have several inputs from handheld FRS and/or GMRS
>>radios, which have several 'calling tone warble'
>>options, one of which sounds like a typical electronic
>>phone. I was hoping to be able to pick two tones
>>from each of these, and to be able to identify which
>>user was calling. I MIGHT be able to pick one tone,
>>and detect the time-domain pattern. Hmmm.
>>My application is for access to my home control system and
>>communications systems from FRS radios used by family members,
>>and from the phone system. My most immediate need is to
>>be able to turn on the "road" lights when arriving late at night.
>>But once I get into the system, lots is possible.
The most vexing problem with using what's built into the radio is that
anyone with another radio and a little patience and good ear can
duplicate the tones and bingo! turn on or open your whatever.
I'd make a small handheld oscillator, probably Wien Bridge, with an
earphone on the output that's loud enough to be heard on the radio when
it's held up to the mic during transmit. At the receiver, this single
tone would then be used to verify that it was really my radio doing the
transmitting. But then I'd still use the other tones to do the 'heavy
If you use two tones with a push button for each, you could have more
than one set of control functions. With a Wien Bridge osc, it's easy to
do this because the tone control elements are two caps and two
resistors. All you have to do is use a switch to change the two
But whatever you do, it's probably a really bad idea to add an
acknowledgement to the receiver because then anyone can remotely tell
how well they're doing at cracking your codes. If you just have the
lights turn on without any ack, then the cracker would have to be within
sight to watch the results of his actions as he fiddled around.
Oh, one other thing. Probably more important than whatever was
discussed here previously. You might be interested in this URL:
http://www.aaaremotes.com/ They have some small keychain remote
transmitters and receivers for under fifty bucks. The nice thing about
these is that they have the built-in security codes.
> With the right system you can switch things on and off remotely.
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