Mobile Controlled Home Appliances without Microcontroller

Introduction

Sometimes unfortunately we may forget switch off the appliances while going to the outside and we face the problems to switch off these devices when we are out of home.

Till now we have seen so many circuits to control the devices or appliances from the remote place but the main advantage of this circuit is simple because we are not using any micro controller in this circuit and it uses the components which are easily available in the market.

Mobile Controlled Home Appliances Circuit Principle:

The main principle used in this circuit is DTMF communication. DTMF is acronym for Dual-Tone Multi-Frequency. When you make a call to customer care service they will ask you to press the numbers to provide the appropriate services. If you think about how they are recognizing the pressed number then DTMF comes on the picture.

If you press the button in your mobile phone then a tone is generated with 2 frequencies. These 2 frequencies of the tone are row and column frequencies of that particular button. For example if you press the button 1 then a tone generated with the sum of 697 Hz and 1209 Hz. The below table show you the row and column frequencies of a DTMF keypad.

Idea Concept:-

• What had been thought impossible at one time was achieved by man.
• As technology advanced man was able to control everything from one place.
• Controlling electrical appliances with mobile is one of the examples.
• This makes the use of DTMF(Dual Tone Multi Frequency) technique.
• The DTMF Decoder circuit is made using M8870 Decoder IC.
• Just connect your cell phone headset (headphone) jack to the mobile phone and then mobile control electrical appliances and electrical equipment via DTMF key pad of your cell phone.

§  Block diagram:-

What is DTMF (Dual Tone Multi Frequency)? DTMF is a common communication term for touch tone phones. The tones formed when dialing on the keypad (DTMF digits or DTMF number) on the phone can be used to characterize the digits, and some different tone is used for each digit. DTMF signaling is mainly used in DTMF phones, telephone switching system.

• How DTMF decoder works?

Yet, there is always a possibility that a random sound will be on the similar frequency which will trip up the DTMF sounds system. It was recommended that if two tones were used to represent a digit, the probability of a false signal happening is ruled out, thus the name ‘Dual Tone’. This is the basis of using dual tone in DTMF communication. DTMF dialing uses a keypad with 12 or 16 buttons. Each key pressed on the keypad generates two tones of particular frequencies, so a voice or a random signal cannot mimic DTMF signaling tones. One tone is generated from a High DTMF frequency group of tones and the other from Low DTMF frequency group.

• When a button is pressed, both the row and column tones are generated by the telephone or touch tone instrument.
• These two tones will be distinctive and different from tones of other keys. So there is a low and high frequency associated with a button, it is essentially the sum of two waves is transmitted.
• This elementary principle can be extended to a range of applications.

DTMF Frequencies generated on Key press: The frequencies generated on pressing different phone keys are shown in the Table.

Button	Low DTMF frequency (Hz)	High DTMF frequency (Hz)
1	697	1209
2	697	1336
3	697	1477
4	770	1209
5	770	1336
6	770	1477
7	852	1209
8	852	1336
9	852	1477
0	941	1336
*	941	1209
#	941	1477

DTMF signals can be transmitted over a radio to switch ON or switch OFF home appliances, flash lights, motors, cameras, warning systems, irrigation systems and so on. These encoded data can be stored and processed in a microcontroller to perform different tasks.

Actual working and Circuit diagram:-

Working of this home automation electronic project

• Our project uses M-8870 DTMF decoder IC which decodes tone generated by the keypad of cell phone.

• When you press any key on your mobile phone while call is in progress, the other person will hear some tones corresponding to the keys pressed. These tones are based on the DTMF (Dual Tone Multi Frequency) technology.

• Data is transmitted as pairs of tones. The receiver detects the valid frequency pair and gives the appropriate BCD code as the output of the DTMF decoder IC.

• DTMF signal can be tapped directly from the microphone pin of cell phone device.

• See the figure below. Cut the microphone wire and you will be able to see 4 wires. Among these wires you need only 2 wires- Ground and Right as shown in figure.

• Select the right wire and connect it as the DTMF input to the decoder circuit. Ground should be connected to common ground of our circuit.

• The signals from the microphone wire are processed by the DTMF decoder IC which generates the equivalent binary sequence as a parallel output of Q1, Q2, Q3, and Q4.

Table showing DTMF Low and High frequency tones and decoded output:-

• The output Q4 from the DTMF decoder IC is fed to the clock input of IC 7474 D flip flop which acts as a buffer to the output from M8870 DTMF decoder IC.

• IC7474 is configured as Toggling mode, that is if it gets a clock pulse the output of this IC (Pin 5) sets to high and further clock pulse resets back the IC. (The outputs toggle whenever a key is pressed).

• When we press and release any of the keys among 1, 3, 5, 7, 9 and *, the DTMF decoder IC generates a high pulse which acts as a clock to our flip flop and sets the output flip flop to high.
• The output of flip flop is connected to the relay driver circuit via 100Ω resistor; this output energizes the relay coil through BC547 transistor and turns ON the bulb that is connected at the normally open terminal of relay circuit.

Advantage:-

• Quick response is achieved.
• Construction is easy.
• Easy to maintain and repair.
• Comparatively the operation cost is less.  
• Design is efficient and low cost.
• Power consumption is low.
• Controlling electrical devices wirelessly
• Saves electricity (when we forget to switch off and go out).
• We can control appliances from any place round the globe.
• No coding is required.

Disadvantages:-

•      This system is not capable of displaying the feedback status of the devices being operated.

•      This system needs a cell phone to be placed in circuit.

•      Number of electrical appliances that can be controlled by this circuit  is limited

Proteus Diagram

Layout

Future scope:-

In future we can add feedback system to know actual status of device… for this purpose we can add camera at the receiver so that we can check current status of device

Conclusion:-

This project demonstrates the remote access of the electrical appliances using the Dual tone multi-frequency technology, eliminating the use of manual switches itself.