Mini Tracker

Posted on Feb 7, 2014

A grasshopper is a switch that is ready to go off at any time. A piece of plastic is placed between two switch contacts to keep them apart and connected to cotton thread fixed to the floor. When the object is moved, the cotton pulls the plastic out of the switch and the bug is turned ON. A bug like this would make an ideal detector to track down a

Mini Tracker
Click here to download the full size of the above Circuit.

nything going astray. By attaching it to the product under surveillance, you can follow its removal and maybe turn up quite a few surprises. The Mini Tracker transmits a very short burst of carrier which produces a blank spot on the FM dial - commonly called silence.  Normally, a lot of background noise called snow  is picked up by a radio when it is tuned to a frequency between the stations. The change between silence and snow produces a click  or beep  and this is the noise produced by the project. No actual beep-tone  is produced - just a change in signal quality. The carrier (or silence) is emitted about twice a second. The circuit consists of two building blocks - both are oscillators. The first operates at a very low rate (low frequency - about 2Hz) and the other operates at approx 90MHz. The first is a square-wave oscillator with a very short ON time,  while the other is a sine-wave. The only thing they have in common is a feedback component,  to create and maintain oscillation. In all other respects they are different. The first point we need to cover is the fact that the first "building block" is separated from the battery via a 1k resistor. This is very important as the Pulse Generator takes a very high current when it is "active. " We say "high current" in relative terms as the whole circuit takes very little average current as it is active for very short bursts. But the current is high during the short...

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