DTMF Cell Phone controlled Home appliances- Engineering automation project

Do you think that you can control your home and office electrical appliances using your cell phone? Yes.! you can... Here is a simple home controls home automation electronic mini project circuit diagram for engineering students, to control any electrical appliances using mobile phone without using a microcontroller. This circuit makes use of DTMF (Dual Tone Multi Frequency) technique. We have already posted on What is DTMF and DTMF decoder circuit using M8870 decoder IC.

• What is DTMF? How are DTMF Tones Generated?
• DTMF Decoder circuit schematic using M8870

This home appliances control or home automation project also uses the same DTMF decoder circuit section with little modifications to control home and office electrical appliances. Just connect your cell phone headset (headphone) jack to the mobile phone and then mobile will control electrical appliances and electrical equipment through the DTMF key pad of your cell phone. Here for demonstrating, we are controlling an electrical bulb using this circuit project but you can extend this circuit to control many electrical devices with some modifications using 4x16 decoder IC.

Circuit diagram of mobile controlled home appliances

                                                      (Click on the image for enlarged view)

Components required for home automation

1. Regulated power supply
2. DTMF decoder IC (M-8870)
3. Resistors (100Ω; 100kΩ; 70kΩ; 390kΩ)
4. Capacitors (0.1µFx 2)
5. Crystal oscillator (3.579545MHz)
6. IC 7474 D flip flop
7. BC547 Transistor
8. 6V relay

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

Button	Low DTMF frequency (Hz)	High DTMF frequency (Hz)	Binary coded output
			Q1	Q2	Q3	Q4
1	697	1209	0	0	0	1
2	697	1336	0	0	1	0
3	697	1477	0	0	1	1
4	770	1209	0	1	0	0
5	770	1336	0	1	0	1
6	770	1477	0	1	1	0
7	852	1209	0	1	1	1
8	852	1336	1	0	0	0
9	852	1477	1	0	0	1
0	941	1336	1	0	1	0
*	941	1209	1	0	1	1
#	941	1477	1	1	0	0

• 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.

Probe further: Transistor inductive load driver circuit with animation

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Pin out of M8870 DTMF decoder, 7474 flip flop IC & BC547

• M8870 DTMF Decoder IC pin out
• 7474 D flip flop pin out
• BC547 Transistor pin out

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