The cell phone call alert security system circuit which needs to be installed incorporates a cheap cell phone as the modem which is actually used for triggering the warning calls in the owners cell phone.The above modem cell phone is first attached with its own SIM card as normally done with any cell phone.
For setting up the cell phone, the cover is removed and a couple of wires are neatly connected with the pads which represent the "green" button or the calling button of the phone.
After securing the two connected wires with the green button terminals, the phone is again sealed back to it normal condition.
The external ends of the above wires are then connected to the relay contacts of the control circuit as shown in the figure.
Before the installation, a call is made from the above modem cell phone to the owners cell phone so that it gets recorded inside the green button as the "last call" made from the cell phone.
Now every time the green button is activated thrice, a call gets connected to the owners cell phone.
Since the wires from the call button are connected to a relay, it simply means that if the relay contacts gets energized thrice, would result a call being sent from the above cell phone.
How the Control Circuit Works
The control circuit basically consists of a hold circuit and a pulse circuit.
The "hold circuit section is made up of two NAND gates configured as a timer cum latch circuit. N1 and N2 together with C12 and R14 form a timer circuit, while the resistor R15 keeps the output latched as long as the timer counts and its timing lapses.
After which the output reverts to its original position.
The input of the above latch is connected to a reed relay sensor which may be appropriately centered for initiating the magnetic contacts when a possible intrusion takes place.
The reed relay activates a relay (left side of the diagram) only momentarily via the capacitor C10.
When the above relay contacts close, N1, N2 latch, and generate a negative or a logic low at the output.
This logic low instantly grounds the reset pin of another timer IC 4060.
This immediately prompts the IC 4060 to start counting.
The process generates a set of three pulses at the pin #15 of the IC activating the relay thrice via the relay driver stage. This activates the cell phone modem which starts sending a blank call to the assigned number or the owners cell phone.
Pin #2 makes sure that the IC counting and the output from pin#15 gets locked after the three relay pulses, this is done by sending a high pulse from pin #2 to pin #11 of the IC.
The IC remains in this position for so long as N1 and N2 are in the counting mode after which the output of N2 goes high and the entire circuit is reverted to its original state and back in the alert mode.
The modem cell phone is kept in a charged state by employing a 7805 charger circuit.
This circuit was exclusively designed and invented by "Swagatam".
All Resistors are ¼ watt 5% CFR, unless otherwise stated.
T2 = BC547