View Full Version : I got problem with RSSI

03-04-2010, 04:13 PM
Hi guys,
Im making an Received Signal Strength Indicator(RSSI) for my mobile. Im using a transmitter which I stick on my cell phone and I bind a receiver in on hand. When a thief going to steal my mobile from me the signals strength will go low and my receiver start vibrate so that I will being alert by a vibrator which i fitted in my receiver.
So in receiver im going to use simple 2051 uC. At transmitter i want to use Astable multivibrator which generate low frequency square wave signal.
Now my problem is i want to receive that square wave signal at certain voltage at which my 1 pin of uc will be set condition, only when distance between Tx and Rx is lesser than 1 meter. When distance goes more than 1m, at reciver end i want less than that voltage at which pin of 2051 will get reset. and my main problem is I must feed a pure dc voltage at pin of uC( becoz i dont want 0v that in at any time).
So the basically my problems are
1)If i put antenna(coil) at o/p if Astabale M/V then may i able to transmit square wave?
2) if i use a simple receiver ckt (like putin capacitor and inductor in llel) will i able to receive pure square wave or i get spikes due to inductance and capacitance?
3)How can i get pure dc voltage from receiver? can i get it by rectifying by simple anti parallel combination of diodes?

pls replay me ty

03-05-2010, 02:13 PM
You will have near-field + far-field spurious responses that will nullify or swamp your receiver.
....the mobile phone transmitter is quite powerful ( it can 'cook' your nrain, according to scientists) and you will have to build extensive circuitry to keep thew RF out of unnecessary parts.

The best way is to have an inductive coupling between the Mobile and your Alarm receiver, like an air cored transformer. or a magnetic reed switch that will trigger the external alarm.

we have done this using RFID components.....

03-05-2010, 09:59 PM
Well i dont want to couple my mobile with alarm receiver. Im going to simply stick that alarm rx behind mobile. my alarm rx have separate ckt, freq, and pwr supply. So in this way if my cell phone (its battery) goes down then still other xtra battery will still keep on this security sys. And my main aim is i wont be able to receive more than 4v so that my uC's pin will be reset and it will get acknowledged that mobile is going away. To trigger my alarm im using uC to generate square wave for my piezo buzzer ( im using an amplifier too if sound is not sufficient).