This circuit will allow you to control any electrical gadget from any part of the world through your cellphone remotely, that too without spending a penny for the individual commands.

Circuit Concept

Whether it’s you vehicle, your basement door, your mansion gate or simply the air conditioner of your house, everything can now be switched by just a flick of your cell phone button.

And yes, it’s completely fool proof, meaning no false triggering is possible through any other cell phone signals, it works only through the owners cell phone commands.



The explained circuit must be employed strictly for operating only the following specified equipment:

All domestic electrical appliances like, lights, fans, motors, TV sets, refrigerators, Air conditioners, washing machine, porch lights, garage door, house gate, basement gate or entrance, car ignition, car doors, water heater etc.

The concept has been already discussed in one of my previous articles – How to make a GSM car security system, and the going about is unbelievably simple.

However, the above article deals with a system that involves DC control features and therefore is not suited for controlling AC appliances.

The unit discussed here is a universal device and can be used for operating all types of electrical gadgets from any part of the globe, just by making a single blank call to the systems number.

The system will faithfully respond to every call made from your cell phone and will alternately switch the connected load ON and OFF as per your instructions.



The concept is impeccable, as it has been tested by me thoroughly since last three years with flying results.

Basically the unit employs a very fundamental principle of converting the ringtone of a cell phone into a command output for operating a relay.

This cell phone acts as a modem and is permanently attached with the internal control circuit of the unit. The modem cell phone is initially made ready by putting a SIM card inside it and by configuring the essential assigned numbers into its phone directory.

These assigned numbers are the only numbers to which this modem responds. Therefore you would want to assign only those numbers through which you may like to make a call to the “system”.

For safety reasons more than one number is assigned to the modem so that in case one of your cell phones is out of order or has low battery, you always have the option of using the other cell phone for triggering the system.

The biggest advantage of the GSM cellphone remote control circuit is that, any cheap NOKIA cell phone can be used here as the modem and therefore there’s no fear of the modem becoming obsolete.A simple yet effective cell phone remote control switch details has been discussed here with complete schematics and step by step tutorial.

If you have sufficient prior knowledge of electronics, you should be making this complete unit within a days time. Let's begin the discussion. Basic Concept The idea here is to use an ordinary NOKIA 1280 cell phone as the modem attached permanently with a switching circuit. This entire unit now becomes the receiver unit.

The modem cell phone NOKIA1280 is assigned with desired numbers, for example the owners cell number and a few other numbers of the owners family members.

When the modem cell phone is called through these assigned numbers, the modem ring tone becomes active and this ring tone is applied to the control circuit and is processed for operating a relay and the connected load.

Since the modem cell phone needs to be attached permanently inside the switching unit, it needs to be charged at regular intervals so that it remains functional all the time.

For this, a separate cell phone charger module has also been incorporated along with the main circuit which keeps the modem cell phone battery always up to date and fully charged.

It is quite obvious that the attached cell phone modem will need a SIM card, which will need to be maintained as we do for normals cell phone operations.

Let's learn the building process. You will have first get or procure the following materials or parts for making this unit. I would suggest not to make the Printed board initially, it would better to first test the working over a general board and if thing goes then you would want to transfer it over a well designed P-C-B.

Bill of Materials


All resistors are 1/4w 5% CFR unless otherwise stated.

R1 = 22k

R2 = 220 OHMS

R3,R11,R12 = 100K R13 = 100 Ohms

R4,R6,R7,R9 = 4.7K

R5 = 1K,

R8, R10 = 2.2M

C1,C4,C5 = 0.22uF DISC TYPE

C2,C3 = 100uF/25V

T1,T2,T4,T5 = BC 547B

T3 = BC557 B

ALL DIODES = 1N4148 IC1 = 4093

RL1, RL2 = RELAY 12V/300 OHMS SPDT

JACK = 3.5mm AUDIO JACK

CELL PHONE MODEM = NOKIA 1280

Circuit Diagram



Understanding the Schematic Diagram


The above schematic of the proposed cellphone controlled remote circuit is rather very easy to understand. It may be divided into two main stages, the lower stage consisting of the transistors is a simple audio amplifier, the upper stage consisting of IC is the flip flop triggering stage.
When a signal is present at the 3.5mm jack, which might be the input ring-tone from the cell phone modem., T1, T2 amplifier to some greater level, which is further amplifier by T3, T4 to a level is becomes sufficient for triggering the relay RL1. RL1 instantly connects the supply to the input of the flip flop at C5, via its N/O contacts.

Note that RL1 will remain switched ON as long as the ring tone is present and will switch OFF the moment the ring tone or the signal over the 3.5mm jack is canceled. C3 makes sure that the relay does not get rattled by any insignificant signals or RFs.

L1 has been installed also for the same reason, that is for eliminating unwanted signals and making sure that T3, T4responds only to valid ring-tones.

L1 is a buzzer coil, as used in piezo electric buzzers, or may be hand made by winding 1000 turns of 36SWG super enameled wire over a small ferrite core, size and shape does not matter. Image of L1, inside a buzzer




The period for which RL1 remains switched ON will have no consequence on the flip flop operation, the flip flop will switch ON and OFF in response to every subsequent missed call made from the owners cell phone.

The section comprising the IC 7805 is battery charger section, which needs to be connected to the battery charger input of the cell phone.

The charger will keep the cell phone battery always charged so that it remains functional all the time. The above circuit has been thoroughly tested and confirmed by me, so if you make everything as shown in the above diagram, it should start working immediately.

How to Assign Numbers Inside the MODEM CELL PHONE It's very easy. Just follow the following steps. Save the names and the numbers which are important and through which you want the above unit to be operated.

Next select a particular name-->--press scroll right-->--"contact details" will be displayed-->-- press options-->--scroll down-->-- select "assign tone"-->--select a ring tone which has a sustained, non-breaking tune-->-- do OK. Repeat this for all the desired numbers. Now go to settings, go to tone settings and select "empty", press OK.

That means now you have switched OFF the default ringtone and no ringtone will be audible for any numbers other than the above assigned ones.

So you can be rest assured that the system will not respond to wrong numbers or any unknown numbers. It will respond to only the calls made from the assigned numbers.

How to Power the Unit


The circuit needs to be powered through a DC12V/500mA or 1 Amp SMPS adapter.
The load may be any electrical appliance like lights, fans, AC, fridge or anything that you may like to switch using this system.

Video Clip showing the circuit functioning of the prototype




WARNING AND DISCLAIMER – THE PROPOSED DEVICE MUST BE USED FOR OPERATING ONLY THE COMMON HOUSEHOLD ELECTRICAL SYSTEMS AND PARAMETERS. THE PROPOSED CELL PHONE OPERATED SWITCH MUST NEVER BE USED FOR ANY OTHER INTENTIONS OR PURPOSE WHATSOEVER, AND THE AUTHOR TAKES NO RESPONSIBILITY FOR ANY LOSSES THAT MIGHT OCCUR IN CASE THE UNIT IS USED FOR OPERATING ANYTHING ELSE OTHER THAN WHAT'S BEEN SPECIFIED IN THE ABOVE ARTICLE.

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