Adjustable Signal...radio, bluetooth, etc.

I am trying to figure out how to control a device that will be "off" while in the range of a transmitter (short range...under 10ft) and then turn on when it goes beyond the range of the signal. I would also like it to be an adjustable range. I was thinking the device would be "on" constantly as the transmitter tells it not to activate, but once it leaves the signal range it would activate. 

Any thoughts?

Thank you in advance.

milkyway312 (author) 3 years ago

How about using bluetooth? Is it possible to "dial" the range down and up?

No.

milkyway312 (author)  mpilchfamily3 years ago

Thanks. So, a radio signal is it.

verence3 years ago

Make/Get a radio receiver that outputs a voltage corresponding to the signal#s strength. (Most have a usable signal somewhere as they need it to control the amplifier). Just compare that voltage against a set (or adjustable) reference and when the received signal gets too weak - react. You do not even have to decode the signal itself. It's like acting on the volume of a conversation you hear, without understanding the words or even the language.

Well... that's true for analogue signals using a permanent carrier. For intermittent signals, digital codings or frequency hopping etc., you have to receive the signal itself and get an quality of service indicator. (Like the number of antea bars on your mobile phone)

Of course in the simplest case you can just receive the signal and react on loss of reception.

But be aware that the strength (or loss) of signal is not directly related to the distance between sender and receiver. Other things may weaken the signal: antenna orientation, walls, metal - or even strengthen it: refection, interferences, object near the antenna...