Description

Mobile controlled Home Appliances without Microcontroller

Introduction

         Using this circuit, you can control your home appliances without any microcontroller and programming.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 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.

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 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 the button 1 then a tone generated with the sum of 697 Hz and 1209 Hz. 
• These generated tones are decoded at switching centre to determine which button is pressed. Now we have to use this DTMF tones to control the devices from 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’.

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 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.

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 the on time