[time-nuts] Toy radiolocation and LORAN envelope
brooke at pacific.net
Tue May 27 18:32:20 UTC 2014
The trouble with a transponder is the receiver is a power hog.
One way to mitigate that is to have the receiver operate on a low duty cycle and use a transmit signal that's longer
than the receive period.
The military PRC-68 squad radio used this method and the squelch opened so fast you would not know it worked that way.
PS that radio is the basis of my web page URL.
In "Leash" mode the location tag transmits a pulse (has no receive function) with a low duty cycle and the smart phone
looks for some number of missing pulses in order to sound an alarm.
This is one way the Bluetooth tags work. The smart phone stores it's location every time it receives a ping from the
tag, not all of them just the last known location, so that when the tag goes missing you know it's last location. Some
proprietary smart phone software allows other smart phones to report hearing a tag that's been reported as stolen.
Another mode is "Find or Locate", i.e. where are my keys? This requires the tag to act as a Bluetooth receiver and beep
when queried. This may be the most popular Bluetooth tag mode.
Chris Albertson wrote:
> You don't need much power because the device in the toy only needs to
> transmit for a few milliseconds then shut off. Some transmuter you
> have pings the device in the toy that acts like a transponder. It
> only transmits in response to a "ping". So limey it can be powered
> by a button battery. How to power the receiver? RFID tags are
> devices that are powered by rectifying the RF energy from the antenna
> . Crystal sets work this way also. as for logic, the TI MSP430 can
> run on nano amps of current. and sleep modes use pico amps. So it
> could be powered by a capacitor that is charge from some powerful AM
> broadcast station.
> It turns out that "energy harvesting" (getting power from the
> environment) is a hot tops right now. The simplest method would be
> the solar powered calculator. That tiny little cell runs a uP and an
> LCD screen. The old mechanical self winding watch was another example
> of harvesting energy. You could run the receiver and logic on
> harvested energy and then use the coid cell battery for a transmitter.
> Your locator device would measure time of flight to the toy and its
> own location via GPS. As you move the locator it gathers data used
> for a solution. All the "smarts" is on the hand held locator that
> has a high power transmitter, sensitive receive, GPS and a computer.
> The device in the toy is a simple transponder.
> In "monitor mode" the locator would request a micro-power ping (not
> using the coin battery, just the capacitor. from the toy and use a
> large non-mobile antenna and would alarm if the time of flight
> You'd want some frequency that would go through walls and trees and in
> some band that is legal for such stuff.
>>> A friend of mine recently suffered a theft so I thought about the
>>> to embed little marker transmitters in some object usually left in the
>>> (like bicycles for example), and have inside the house a system that
>>> constantly monitors them for unwanted movement,
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