In this project, I will show you how to design a simple circuit called Mobile Controlled Home Appliances without Microcontroller. That’s right. Using this circuit, you can control your home appliances without any microcontroller and programming.

Mobile Controlled Home Appliances without Microcontroller Image 2

Introduction

Sometimes, unfortunately, we may forget to switch off the appliances like fans and lights while going outside and as a result, we end up paying the price for it. To solve these types of problems, this article explains to you how to design a simple circuit, which will on the devices remotely and devices will off automatically after the specified time interval.

Till now we have seen so many home automation projects that control the devices or appliances from the remote place but the main advantage of this circuit is simple because we are not using any microcontroller 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 an 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 into the picture.

If you press the button in your mobile phone, 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 button 1 then a tone generated with the sum of 697 Hz and 1209 Hz. The below table shows you the row and column frequencies of a DTMF keypad.

Frequency Range

These generated tones are decoded at the switching center to determine which button is pressed. Now we have to use these DTMF tones to control the devices from the remote area. To decode these DTMF tones at receiver we need to use a DTMF decoder. Decoder IC converts these tones into the digital form. For example, if you press number ‘5’ in mobile keypad then the output of DTMF decoder is ‘0101’.

Cellphone Controlled Home Appliances Circuit Diagram without Microcontroller

Mobile Controlled Home Appliances without Microcontroller Circuit Diagram

Circuit Components

  • MT8870 DTMF decoder
  • 5V Relay Module
  • 230V, 50 Hz AC motor (optional)
  • BC547 Transistor
  • 3.579545 MHz crystal
  • 3.5mm audio jack
  • LED
  • 1N4007 Diode
  • 0.1uF Ceramic capacitors – 2
  • 20pF Ceramic Capacitors – 2
  • Resistors (1/4 watt) – 1KΩ, 100KΩ x 2, 300KΩ
  • Connecting wires
  • Breadboard

Mobile Phone Controlled Home Automation System Design without Microcontroller

It would be best if you choose dedicated modules for the DTMF Decoder and relay as building them from scratch might be tedious. If you are going with modules, then all you need to do is to make a few small connections using jumper cables as all the components are readily placed.

Mobile Controlled Home Appliances without Microcontroller Image 3

Connect an audio cable in the 3.5mm audio jack between the receiver mobile phone and the DTMF Receiver board. The D0 pin (usually marked as Q1) is connected to the input of the relay module.

Working

The main components in this circuit are MT8870 DTMF decoder (a variant called CM8870 IC is used here). When you make a call to the mobile which is connected at the receiver end, the MT8870 IC provides a high pulse at 15th pin after receiving a valid signal. Now if you press 1 from the mobile the output of the decoder IC at pins Q1, Q2, Q3, and Q4 will be 1, 0, 0 and 0 respectively.

As the Q1 pin is connected to the input of the relay, it will be activated and as a result, the load will be turned ON. To turn off the load, press any number that makes Q1 as 0 i.e. 2 for example.

The following tables show the Binary outputs corresponding to the buttons pressed on the mobile phone.

DTMF Decoded Frequency Output Table

DTMF Decoded Frequency Output Table

How to Operate a DTMF Controlled Home Automation System without Microcontroller?

  • Give the connections as per the circuit diagram.
  • While giving the connections, make sure that there is no common connection between AC and DC supplies.
  • Insert the audio jack to the receiver mobile and keep the receiver mobile in auto-answer mode.
  • Receiver mobile should be in general profile and keypad tones should be in sound mode.
  • Now make a call to the receiver mobile as it is in the auto answer mode it will pick up the call automatically.
  • When the call is attended, press number 1 on your mobile. This will activate the relay.
  • To turn off the relay, press 2.

Mobile Controlled Home Appliances without Microcontroller Image 1

DTMF Mobile Controlled Home Appliances Circuit Applications

  • Used to control the home appliances
  • We can control the robot using this technology
  • This circuit is used to control the water tank motor by setting them on time

Circuit Advantages

  • We can avoid the wastage of power
  • We can control the devices from long distances also

Circuit Limitations

  • Security is not provided, anyone can control by making a call to the receiver mobile
  • The number of devices which we can connect to the circuit is limited.

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