In general, switches are utilised to regulate the equipment in our homes. Many technologies are now being employed in home automation system projects. This article discusses how to use DTMF technology to control home appliances.
The word DTMF stands for Dual Tone Multi Frequency. Think about it: when you call customer service, they’ll tell you to push 1, 2, or any other number. When you dial a phone number, your phone performs a specific operation. All of this is due to DTMF. A tone of two frequencies is generated when a button on your mobile keypad is pressed. Row and column frequencies are the terms used to describe these tones.
Row frequencies are often low, while column frequencies are typically high. These DTMF frequencies are chosen in such a way that they have no harmonic relationship with one another, ensuring that they do not create the same tones. To compensate for the high-frequency roll off of voice audio systems, the column frequencies are significantly louder than the row frequencies.
We’ve discovered that pressing each key on the keypad produces a tone that is distinct from the others. These tones should now be used in our gadgets. As a result, this DTMF encoder can be found in mobile phones. The DTMF decoder IC HT9107B may convert keypad output to digital format. This IC’s interface to a microcontroller is shown below.
- DTMF Controlled Home Appliances Circuit Principle:
- DTMF Controlled Home Automation System Circuit Diagram:
- Circuit Design of DTMF Controlled Home Appliances:
- How to Operate the Circuit?
- DTMF Controlled Home Automation System Project Output Video:
- Download Code
- Advantages of DTMF Controlled Home Automation System Circuit:
- Limitations of DTMF Controlled Home Appliances:
DTMF Controlled Home Appliances Circuit Principle:
The fundamental idea behind this circuit is to use DTMF technology to control appliances like lights and fans. Your phone has a DTMF encoder, and the decoder is an HT9107B IC. A 1nf capacitor is attached to the mobile jack. Two wires make up a mobile jack (Red and black). The decoder IC is linked to the red wire, while the black wire is grounded. When a button on the phone is pressed, a tone is generated, which is deciphered by the decoder IC and delivered to the ATMEGA8 controller. The controller then looks for input and outputs output based on the code that has been written to it.
This circuit mainly consists of the following components.
- ATmega8 microcontroller U1
- HT9107B IC
- AC Load
- Resistors – R1, R2 and R3
- Capacitors – C1, C2, C3 and C4
- Crystal Oscillator X1
Circuit Design of DTMF Controlled Home Appliances:
The decoder IC consists of an inbuilt operational Amplifier. The output of op-amp is given to the pre-filters to separate low and high frequencies. Then it is passed through frequency and code detector circuits, thus 4-bit binary code is latched.
Through a sequence of resistors (100 kilo-Ohm) and capacitors, the tone from the phone is transferred to the op-amp (1nf). Pin1 of the DTMF IC, which is a non-inverting pin, is connected to Vref pin4. Pin3 is the operational amplifier’s output, which is sent back to pin 2 through a 100 kilo-Ohm resistor. A crystal oscillator with a frequency of 3.579545 MHz is attached to pins 7 and 8. When a DTMF tone is detected, the 15th pin rises high; otherwise, it remains low. The steering circuit, which consists of EST, RT/GT, and a resistor (10k), and a capacitor, performs the frequency detection and digitalization of the signal. The decoded output is produced by pins 11 to 14.
The output pins of DTMF IC (i.e. 11 – 14) are connected to PB0-PB3 pins of controller. Output pins of the controller i.e PD0 and PD1 are connected to relay. Relay output is connected to AC source i.e. light or fan.
Relay acts as a switch. It produces isolation from different parts of the circuit. In our project it is used to switch AC load using 5v which is maximum voltage from controller. Relay used here is magnetic relay.
How to Operate the Circuit?
When the circuit is turned on, the controller checks the inputs on a regular basis. When the number one is pressed on the mobile keypad, the decoder IC decodes the tone and outputs 1(0001), which is passed to the microcontroller, which provides a high output at the PD0 pin. The relay is attached to PD0. The circuit is switched by a relay, and the fan is turned on as a result. In the same way, if the received input is 2, the fan is turned off. If the received input is 3, the light is turned on; if it is 4, the light is turned off.
DTMF Controlled Home Automation System Project Output Video:
Advantages of DTMF Controlled Home Automation System Circuit:
- One can control home appliances from anywhere.
- It reduces wastage of electricity when we forgot to switch off the lights & fans and gone outside.
- It is very low cost compared to other technologies like GSM.
Limitations of DTMF Controlled Home Appliances:
- No security. Anyone can control the appliances by calling the mobile connected to module.
- Number of appliances is limited as our mobile can generate only 16 tones.
To know more about this concept, read the post – Home Automation System and its Applications
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