In this project, I will demonstrate how to create a simple circuit called “Mobile Controlled Home Appliances without a Microcontroller.” Yes, you can manage your household appliances without the need for a microprocessor or any programming skills using this circuit.
Outline
- Introduction
- Mobile Controlled Home Appliances Circuit Principle
- Cellphone Controlled Home Appliances Circuit Diagram without Microcontroller
- Circuit Components
- Mobile Phone Controlled Home Automation System Design without Microcontroller
- Working
- How to Operate DTMF Controlled Home Automation System without Microcontroller?
- DTMF Mobile Controlled Home Appliances Circuit Applications
- Circuit Advantages
- Circuit Limitations
Introduction
Unfortunately, there are instances when we inadvertently leave devices like fans and lights turned on when we leave a room, resulting in unnecessary energy consumption and costs. This article aims to demonstrate how to construct a simple circuit that can remotely activate these devices and automatically switch them off after a suitable time period, addressing such challenges.
While there are numerous home automation projects that enable remote control of appliances, the distinct advantage of this circuit lies in its microcontroller-free design. Instead, it relies on readily available components. In a prior article, we explored a DTMF-controlled home automation system circuit that employed a microcontroller.
Mobile Controlled Home Appliances Circuit Principle
The fundamental principle employed in this circuit is DTMF communication, which stands for Dual-Tone Multi-Frequency. When you interact with customer service or automated phone systems, you are often asked to press specific numbers to access the services you need. DTMF plays a crucial role in how these systems recognize the numbers you press.
When you press a button on your phone, it generates a tone composed of two distinct frequencies. These two tones correspond to the row and column frequencies associated with the specific button you pressed. For instance, pressing button 1 produces a tone with frequencies of 697 Hz and 1209 Hz. The table below illustrates the row and column frequencies of a DTMF keypad.
The tones produced are sent to a switching center, where they are processed to determine which button was pressed. To remotely control devices using these DTMF tones, we need a DTMF decoder at the receiver end. This decoder IC is responsible for converting these tones into a digital format. For example, if you press the number ‘5’ on your mobile phone, the DTMF decoder will output ‘0101’.
Cellphone Controlled Home Appliances Circuit Diagram without Microcontroller
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
- Bread board
Mobile Phone Controlled Home Automation System Design without Microcontroller
Using dedicated modules for the DTMF Decoder and relay is recommended over building them from scratch. When utilizing modules, you only need to establish a few small connections with jumper wires since all the components are already incorporated.
Connect the receiver mobile phone and the DTMF Receiver board with an audio wire in the 3.5mm audio jack. The D0 pin (usually labelled Q1) is connected to the relay module’s input.
Working
The MT8870 DTMF decoder is a crucial component of this circuit (in this case, a variant known as the CM8870 IC is utilized). When you make a call to the connected mobile phone, the MT8870 IC, upon receiving a valid signal, generates a high pulse at its 15th pin. For instance, if you press the number 1 on your phone, the decoder IC will produce corresponding outputs of 1, 0, 0, and 0 at its pins Q1, Q2, Q3, and Q4, respectively.
As the Q1 pin is connected to the relay’s input, it becomes active, turning on the load. To deactivate the load, you simply need to press any number that corresponds to 0 at the Q1 pin, such as 2.
The following tables shows the Binary outputs corresponding to the buttons pressed on the mobile phone.
How to Operate DTMF Controlled Home Automation System without Microcontroller?
- Connect the wires according to the circuit schematic.
- Make sure there are no common connections between the AC and DC supply while making the connections.
- Keep the receiver mobile in auto answer mode by connecting the audio jack to it.
- The receiver phone’s profile should be set to general, and the keypad tones should be set to sound.
- Make a call to the receiver’s phone, which will automatically pick up the call because it is in auto answer mode.
- When the call is answered, dial number one on your phone. The relay will be activated as a result of this.
- Press 2 to turn off the relay.
DTMF Mobile Controlled Home Appliances Circuit Applications
- It’s used to regulate the appliances in the house.
- We can use this technology to control the robot.
- This circuit is used to set the on time for the water tank motor.
Circuit Advantages
- We can avoid the wastage of power
- We can control the devices from long distances also
Circuit Limitations
- No security is given, and anyone can manage the system simply dialling the receiver’s phone number.
- The number of devices that can be connected to the circuit is restricted.
