The post presents a simple cellphone triggered remote control circuit that can be applied as a cellphone operated remote car starter. The unit would cost less than $20 to build.

I have already covered quite a few interesting cellphone remote control circuits in this blog, all of which can be implemented to control or toggle some electrical equipment remotely using ones own cell phone, exclusively.

How it Works

The basic cellphone controlled relay circuit stage involved in all the previous circuits can be also effectively utilized for starting the ignition system of a vehicle, through the owners cell phone. The schematic for the same may be witnessed below and may understood with the following explanation:

The design is basically a transistorized audio amplifier circuit, which is positioned for amplifying the assigned ringtone from the adjoining cell phone modem. The cellphone shown with the circuit stays permanently attached with the circuit and forms the integral part of the whole system.

The diagram shows a NOKIA 1280 cellphone as the modem, however any cheap cellphone may be employed for the purpose provided the cellphone includes the "assign tone" feature discretely for the particular selected numbers.

The number of the owner or the user is first stored and assigned with a suitable ringtone available within the cellphone modem so that the modem responds only to the owners phone and not to any other irrelevant numbers. The default ringtone of the modem is set to "empty" in order to mute all other unwanted calls.

When the owner calls the modem cellphone, the ringtone is detected by the circuit and amplified to a level sufficient for the relay to get energized. The relay stays energized for so long as the call remains connected.

Configuring the Relay Contacts

Since the relay contacts are configured or integrated with the ignition switch of the car, immediately triggers the ignition system of the vehicle starting the engine and the whole system.

A feed back from the activated alternator makes sure that the relay is instantly shut off irrespective of the call duration from the owner's cellphone.

The car ignition thus is able to start without the owner or the driver having to get inside the car and go through the manual operations. The car starts remotely through the owner's cell phone, a fail proof and a foolproof procedure yet as cheap as anybody can think of.

Parts List

R1 = 22k
R2 = 220 Ohms,
R3 = 100K,
R4,R6,R7 = 4K7
R5 = 1K
R8 = 33K
R13 = 100 ohms,
T1, T2, T4, T5 = BC547
T3 = BC557,
C1 = 0.22uF
C2,C3, C4 = 100uF/25v
D1, D2 = 1N4007
L1 = 40 mH coil, example: a piezo buzzer coil will do.
diode = 1N4007
Relay = 12V/SPDT
Modem = NOKIA 1280

The charger section is shown in the diagram, and needs to remain connected permanently with the attached cellphone modem.

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