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. 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. We have already seen How DTMF Controlled Home Automation System Circuit Works using Microcontroller in the earlier post.
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.
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’.
Cellphone Controlled Home Appliances Circuit Diagram without Microcontroller:
- MT8870 DTMF decoder
- NE555 timer IC
- 5V relay
- 230V, 50 Hz AC motor
- BC548 transistors – 2
- 3.579 MHz crystal
- Pot – 4.7M ohm
- 2.5mm audio jack
- red LED
- Electrolytic capacitor – 470uF
- 1n4007 Diodes – 5
- 0.1uF Ceramic capacitors – 3
- Resistors (1/4 watt) – 150k, 1k, 390k, 10k, 100k, 2.2k, 1M, 220
- Connecting wires
- Bread board
Mobile Phone Controlled Home Automation System Design without Microcontroller:
The main components in this circuit are MT8870 DTMF decoder and 555 timer. Here 555 timer operates in monostable mode. When you make a call to the mobile which is connected at the receiver end, MT8870 IC provides high pulse at 15th pin after receiving a valid signal. Now if you press 7 from the mobile the output decoder IC will trigger the 2nd pin of 555 timer. As a result the output at 3rd pin of 555 timer becomes high, so that transistor Q2 starts conducting because of this LED and device on. The device on time can be varied by varying the Pot RV1 and capacitor C4. The device on time can be calculated using the formula
Time = 1.1 * RV1 * C4 sec.
In the above circuit device become on only when all the outputs of DTMF decoder (pin 11, pin12, pin13 and pin15) are high. To make all the outputs of DTMF decoder high we need to press number 7 from the dialed mobile.
[Also Read: How To Make an Adjustable Timer ]
How to Operate 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.
- Solder a two pin connector to the audio jack
- 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 ring stops press number 7 in your mobile, now you can observe that both LED and device will on for some time and switches off.
DTMF Controlled Home Automation System without Microcontroller Circuit Advantages:
- We can avoid the wastage of power
- We can control the devices from long distances also
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 the on time
- Security is not provided, anyone can control by making a call to the receiver mobile
- Number of devices which we can connect to the circuit is limited.