This document describes a DTMF (Dual Tone Multi-Frequency) based remote control system using a mobile phone. It consists of a DTMF decoder, microcontroller, relays, and appliances. The system allows controlling up to 4 appliances by pressing number keys on the mobile phone. When a key is pressed, the DTMF decoder converts the tones to digital signals for the microcontroller. The microcontroller then activates the corresponding relay to turn the appliance on or off. The system offers remote control of appliances with advantages of quick response, easy operation, and low cost.

2. CONTENTS
 Introduction
 Block diagram
 DTMF – working
 Components used
 Working
 Software used
 Advantages
 Applications

3. INTRODUCTION
• 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.

4. BLOCK
DIAGRAM

5. DTMF
decoder
Micro
-
contr
oller
Relay
1
Relay
2
Relay
3
Relay
4
Appliance
2
Appliance
3
Appliance
1
Appliance
4
4 bit
binary
digit
1input
2
3
4
5
6
ULN
2803
7

6. DTMF keypad frequencies
DUAL TONE – every button on keypad is characterised
by two different tones
MULTI FREQ.- because it use a mixture of two pure tone
(pure sine wave) sounds
Hz 1209 1336 1477
697 1 2 3
770 4 5 6
852 7 8 9
941 * 0 #

7. WORKING OF DTMF DECODER

8. KEYPAD TONE DECODING

9. COMPONENTS USED

10. Transformer &
Rectifying unit
Headphone –DTMF receiver
Receiver – a GSM cellphone

11. Mcrocontroller unit
DTMF to binary conversion Load driving unit

12. Voltage Regulator - 7805
2 pin connector

13. Block diagram of Linear Regulated
power supply

14. Inside voltage regulator
• employs a pass element serving as a variable resistor
which forms a voltage divider with the load.
• The pass element can be a transistor placed in
between the unregulated dc voltage and the desired
regulated dc output.

15. DTMF decoder MT8870

16. Microcontroller AT89s8253

17. Pin diagram : Atmel AT89s8253

18. LED’s
Resistors

19. Crystal Oscillators

20. PCB Relay (electromagnetic)
Relay driver IC - ULN 2803

21. Pin diagram : ULN2803
Darlington pair of
transistors

22. Darlington pair of transistors
Very high gain
of the order
10,000 to 100,000

23. WORKING
• The first step is to call the reciever phone.
• Next we press the required digit on keypad of
sender phone to give an input.
• DTMF decoder converts the dual tone. frequency
into a digital signal- 4 bit binary.
• Output from decoder becomes the input to the
microcontroller via port 1.
• Processing of the digital signal takes place and an
input is generated for relay driving IC-uln2803.

24. WORKING
• The driving IC uln 2803 is actually a router which
controls the operation of relays and susequently
the appliances.
• Each appliance has a different relay unit
controlling its on-off operation.
• In this project we control 4 appliances as:
• Key 1,2 : appliance 1 ON & OFF respectively
Key 3,4 : appliance 2 ON & OFF respectively
Key 5,6 : appliance 3 ON & OFF respectively
Key 7,8 : appliance 4 ON & OFF respectively
Key 9 : all appliances gets ON
Key 0 : all appliances gets OFF

25. SOFTWARE USED
Mikro C Express PCB

26. APPLICATIONS
• This system can be used in industrial applications.
• This system can be employed in houses ,where people
often forget to switch off electrical appliances
• This system can be used to control AC’s to set the room
temperature
when we are outside
• We can extend this circuit to control many electrical
devices with some modifications using 4 x16 decoder IC.

27. ADVANTAGES
• 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.