to detect by any external device if there is incoming call to mobile

1. EM
N. SHARMA
TESTED
CELLULAR PHONE INCOMING
CALL DETECTOR
Here is a circuit which detects when a
call is incoming in a mobile phone by
means of a flashing LED. It can detect
even when the calling tone of the device
is switched-off.
It must be placed a few centimeters from
the mobile phone, so that its sensor coil
L1 can detect the field emitted by the
phone receiver during an incoming call.
Working:
The sensor coil L1 detects the signal and
the detected signal is amplified by
transistor Q1 and drives the monostable
input pin of IC1. The IC's output voltage
is doubled by C2 & D2 in order to drive
the LED1 at a suitable peak-voltage.
Stand-by current drawing is less than
200µA.Sensitivity of this circuit
depends on the sensor coil type. L1
can be made by winding 130 to 150
turns of 0.2 mm. enameled wire on a
5 cm. diameter former. Remove the
coil from the former and wind it with
insulating tape, thus obtaining a
stand-alone coil.
R3
1M
IC1
7555
1
6 3
8 4
7
2
+
1.5V
Batt.
-
R2
3.9K
L1
Q1
BC547
C1
0.1µ
63V
C2
0.1µ
63V
R1
100K
C3
220µ
25V
LED1
RED
D1
1N5819
A commercial 10mH miniature
inductor, usually sold in the form of a
tiny rectangular plastic box, can be
used satisfactorily but with lower
sensitivity.
IC1 must be a CMos type: only these
devices can safely operate at 1.5V
supply or less.
R.C. Mathur