|
TRACKING |
Lets you find things, using an FM radio to pick up the level of "snow" compared to the level of "silence."
See also: Mini Tracker Beeper Bug
This circuit can be used to track an item, using an FM radio.
It is turned on via the flashing LED.
The flashing LED is powered via the 2k2 resistor and base-emitter junction
of the BC557 transistor. When the LED is not flashing, the current taken by
the chip inside the LED consumes very little current and the 10k resistor
supplies some of the current so that the BC557 is not turned on.
This means the 100MHz oscillator section is not turned on and the circuit
consumes very little current.
The RF output is zero. But when the chip inside the LED counts 0.5 seconds,
it turns on the LED and this current turns on the BC557.
The transistor pulls the 10k resistor on the collector to the 3v rail and
this activates the oscillator.
The circuit produces a carrier and this is detected on an FM radio as
"silence."
When the LED turns off, the carrier stops and background noise is heard from
the radio.
This is a clever way of producing a beep without the necessary beep
circuitry.
No kits are available for this project, however the mini tracker board can
be used and modified to take the additional components.