Cell Phone Controlled Relay

            Now a days all of them are using various types of cell phone in the world. Imagine that from your cell phone you can control a relay which is connected to you home gate lights or other equipment's in the house. So i build a circuit for this application.While calling to someone, if we press any button in the cell phone a tone produced and the receiver can heard.This tone is called DTMF (Dual Tone Multi Frequency).For more about DTMF, see my previous post.The working of the circuit is based on this principle. 

                                                 Click the circuit for enlarging.

DTMF Decoder

      While calling to someone, if we press any button in the cell phone a tone produced and the receiver can heard.This tone is called DTMF (Dual Tone Multi Frequency). DTMF assigns a specific frequency (consisting of two separate tones) to each key so that it can easily be identified by the electronic circuit. The signal generated by the DTMF encoder is a direct algebraic summation, in real time, of the amplitudes of two sine (cosine) waves of different frequencies, i.e., pressing ‘5’ will send a tone made by adding 1336 Hz and 770 Hz to the other end of the line. The tones and assignments in a DTMF system are shown below.

  

Frequencies	1209 Hz	1336 Hz	1477 Hz	1633 Hz
697 Hz	1	2	3	A
770 Hz	4	5	6	B
852 Hz	7	8	9	C
941 Hz	*	0	#	D

      An MT8870 series DTMF decoder is used here. All types of the MT8870 series use digital counting techniques to detect and decode all the 16 DTMF tone pairs into a 4-bit code output. The built-in dial tone rejection circuit eliminates the need for pre-filtering. When the input signal given at pin 2 (IN-) in single-ended input configuration is recognised to be effective, the correct 4-bit decode signal of the DTMF tone is transferred to Q1 (pin 11) through Q4 (pin 14) outputs.The circuit is shown below.

3.5mm Headphone Jack

         3.5 mm Headphone Jack is a 1/8 inch or 3.5 mm headphone jack is an audio socket that accepts a 3.55 mm male pin or audio plug. A small round connector for accepting the pin-shaped plug from a standard pair of music headphone. Below schematic shows the typical diagram of 3.5mm Headphone Jack.

3.5mm Headphone Jack Schematic Diagram 

• 1 – tip : audio out left channel. 
• 2 – 1° ring : audio out right channel. 
• 3 – 2° ring : microphone line in. 
• 4 – 3° ring/sleeve : ground – common for microphone and audio out.

       In circuits we only need the Speaker +ve and the speaker ground. For circuit, Tip pin as the 1 and the ring pin as either the right channel out (pin 2) or left channel out (pin 1). The modified schematic diagram of the 3.5 mm Headphone Jack for circuits is below (for electronics application).

Cell phone controlled car without micro controller

I had made this cell phone controlled car for my project. In every cell phone controlled car there is costly micro controller. But in my car i don't use a  micro controller. so the programming is not need for my car.  So every beginners in the electronics can do this project.

The car can move forward, backward, Left turn, Right turn, Rotating clock wise, Anti rotating clock wise.

The main part of the car is DTMF decoder ic and a motor driver. The DTMF decoder decodes the signals from the mobile and send to the motor driver ic. For every decoded signal there is a movement in the car.

My Old Prototype 

New Prototype 

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Cell Phone controlled home appliances

Prototype of the cell phone controlled home 

appliances