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# Cellular Phone Calling Detector Circuit (1N5819)

2016-02-03 20:32
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This article describes Cellular Phone Calling Detector Circuit (1N5819). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: 1N5819.

This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashingLED. The device must be placed a few centimeters from the cellular phone, so its sensor coil L1 can detect the field emitted by the phone receiver during an incoming call.

Circuit diagram:

#### Figure 1 Cellular Phone Calling Detector Circuit Diagram

Parts:

R1 = 100K
R2 = 3K9
R3 = 1M
C1 = 100nF-63V
C2 = 100nF-63V
C3 = 220μF-25V
D1 =LEDRed 10mm.Ultra-bright (see Notes)
D2 = 1N5819-40V 1A Schottky-barrier Diode (see Notes)
Q1 = BC547-45V 100mANPNTransistor
L1 = Sensor coil (see Notes)
B1 = 1.5V Battery (AA orAAAcell etc.)
IC1 = 7555 or TS555CN CMos Timer IC

Circuit operation:

The signal detected by the sensor coil is amplified by transistor Q1 and drives the constable input pin of IC1. The IC’s output voltage is doubled by C2 & D2 in order to drive the high-efficiency ultra-brightLEDat a suitable peak-voltage.

Notes:
Stand-by current drawing is less than 200μA, therefore a power on/off switch is unnecessary.
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 (e.g. a can). Remove the coil from the former and wind it with insulating tape, thus obtaining a stand-alone coil.
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.
Any Schottky-barrier type diode can be used in place of the 1N5819: the BAT46 type is a very good choice.