How to Build a Cell Phone Controlled Door Latch
Controlling your door lock through your personal cell phone was never this easy. Learn how to build a simple electronic circuit that will help in converting your ordinary door lock into a high security door lock which can be now controlled through your own cell phone.
Your ordinary door lock can be now very easily converted into a cell phone controlled high security door lock. Learn the entire building procedure through some simple instructions and circuit schematics.
Introduction
A very simple configuration using a low cost cell phone (used as a modem) and an electronic circuit can be build to control remotely a high security door lock. Once the unit is built and attached to a door, by simply assigning your personal cell phone’s number inside the modem cell phone, you can alternately lock and unlock a particular door by sending subsequent “miss calls” through your cell phone to it from any part of the world. We use a NOKIA 1202 as the modem cell phone here for the project. Let’s proceed and learn the simple instructions required to complete the project.
How the Circuit Functions?
The basic concept of the project is to detect a particular ringtone from a SIM supporting modem and use it to toggle the electronic circuit and the load (door lock) correspondingly. The very specific and unique ringtone – “Beep Once” or the “No Tone” is available with every NOKIA cell phone. And also this ring can be assigned to any particular fed number of the cell phone. So this ringtone becomes specific only to that particular number and will be sounded every time a call is received from the assigned number. This facility has been ideally exploited here. A 5 volt regulated supply is used to trickle charge the modem round the clock so that its battery is never discharged. This supply also goes to the IC 4093 = pin 14 (+) and pin 7(-). An in-built cut-off system inside every NOKIA cell phone ensures a safe charging.
The circuit functioning may be easily understood with the following explanation.
The FIGURE above shows a simple three transistor amplifier circuit which is basically used as a tone amplifier. On receiving a “miss call” from the assigned number (owner’s cell phone), the modem immediately responds and produces the desired ringtone (“Beep Once”). This tone frequency is collected from the modem’s headphone socket and applied to the tone amplifier’s input. The ringtone is suitably amplified and is used to toggle a relay momentarily. This relay connects a 5 volt trigger pulse to the input of CMOS flip flop circuit and also sounds a buzzer. The flip flop toggles in response to the above action and activates the following transistor/relay locking mechanism. A car central lock has been effectively integrated with an ordinary manual locking shaft to form an excellent door dead bolt. The whole system activates in a push pull manner to alternately lock and unlock the door in response to every subsequent “miss call” from the owner’s cell phone.
Assembled, tested kit available, contact hitman2008@live.in
Parts List
R1=2K7
R2=10K
R3=10K
R4=2M2
R5=2M2
R6=1K
R7=1M
R8= 180 Ohms
R91K
R10=10K
R11=22k
R12=47K
R13=10 Ohm
C1,C2=470uF/25V
C3,C4,C5=0.22uF
C6,C7,C12=10uF/25V
C8 = 0.1uF/100V
C9,C10=1uF/25V
C11=1000uF/25V
All NPN Transistors are BC547 and PNP is BC557
IC2=7805
IC1=4093
All Relays=12V/400 Ohm
Diodes D5- D8=1N5408
Rest all Diodes are 1n4148
Transformer=0-12V/3Amp
Construction Clues and Modem Cell Phone Configuration
Constructing the control circuit is very easy and may be done by just assembling the procured electronic components over a general purpose board by soldering. All the connections should be accurately done with the help of the given circuit schematic. Once the assembly is completed, it’s time to configure the modem cell phone.
The attached modem cell phone needs to be set up through the following steps:
Go to settings and select set the default ringtone as EMPTY. It means now at this position the modem does not produce any ringtone to any incoming calls. Also, switch off the message tone, keypad tone, start up tone etc.
Now feed your personal cell phone numbers (single or many as desired) through which the modem and the lock need to be operated.
Assign the required “beep once” ringtone to all these numbers.
The modem is all set. Integrate it to the control circuit through its headphone socket pin assembly. Also, connect the charging voltage input to it as shown in the diagram.
Your high security door lock is fully ready and can be installed over the door which is to be controlled and will lock and unlock it faithfully on receiving the subsequent “miss calls” from the assigned numbers.
