when the cell phone rings..

[sonaiko]

i found this circuit to build in a site..
**broken link removed**



Parts:

R1____________100K 1/4W Resistor
R2______________3K9 1/4W Resistor
R3______________1M 1/4W Resistor

C1,C2_________100nF 63V Polyester Capacitors
C3____________220µF 25V Electrolytic Capacitor

D1______________LED Red 10mm. Ultra-bright
D2___________1N5819 40V 1A Schottky-barrier Diode

Q1____________BC547 45V 100mA NPN Transistor

IC1____________7555 or TS555CN CMos Timer IC

L1_____________Sensor coil

B1_____________1.5V Battery (AA or AAA cell etc.)


this device supposed to flash the LED when a phone call comes when u place ur cell phone few centimeters away from the sensor coil..

my problem is, i built the circuit, but i didnt know what they meant by "sensor coil" so i used a 10mH inductor as a subtitue.. the circuit is not working! that is part one of the problem..

part two, i really cannot understand what happens exactly when the phone rings and what does that have to do with the coil??!!

can anybody solve those 2 problems plz???

 

[williB]

when the cell phone rings it is also communicating with a tower..
when it talks to a tower it is transmitting electromagnetic waves..
which can be picked up by a coil ..
try using a coil of wire , your inductor may be too small..
EDIT : something like 50 feet of single strand speaker wire might work..just wrap it around something..

 

[sonaiko]

when the cell phone rings it is also communicating with a tower..
when it talks to a tower it is transmitting electromagnetic waves..
which can be picked up by a coil ..
try using a coil of wire , your inductor may be too small..
EDIT : something like 50 feet of single strand speaker wire might work..just wrap it around something..

shall i uncover the wire? or just keep it as it is?

 

[zachtheterrible]

hey sonaiko :lol:

Dont strip the wire. Then the current would not be able to go through the entire wire, it would just short circuit.

 

[Megamox]

hey sonaiko

by looking at the diagram, im guessing by placing the cell phone near the coil which is wound like an inductor, the electromagnetic waves the cell phone uses to communicate with the tower (when it rings!) induce a small voltage in the inductor, this is probably a few milivolts, this is amplified by the self biased transistor network, these arrangements usually have a gain of somewhere between 70 and 150 i think. This is passed onto the 555 timer to trigger it and an indication is given in the output.

Hope this helps