In general, switches are commonly used to regulate equipment in our homes. However, there is a wide range of technologies employed in home automation system projects today. In this article, we will specifically delve into the use of DTMF technology for controlling home appliances.
DTMF, which stands for Dual Tone Multi Frequency, plays a pivotal role in this context. Consider when you call customer service, and they instruct you to press buttons like 1, 2, or any other number. Each time you dial a phone number, your phone performs a specific operation, all thanks to DTMF. It operates by generating a tone consisting of two frequencies when a button on your mobile keypad is pressed, with these frequencies often referred to as row and column frequencies.
Row frequencies, generally characterized by their lower values, are contrasted with column frequencies, which tend to be higher in frequency. The selection of these DTMF frequencies is meticulous to avoid any harmonic relationship between them, ensuring that they do not generate identical tones. To address the high-frequency roll-off inherent in voice audio systems, the column frequencies are intentionally made much louder than the row frequencies.
With the understanding that each key pressed on the keypad produces a distinct tone, it becomes evident that these tones are valuable for our electronic devices. Consequently, this DTMF encoder has found its place in mobile phones, offering a convenient interface for users. To further illustrate its utility, the DTMF decoder IC HT9107B can be employed to convert keypad output into a digital format. The interface of this IC with a microcontroller is detailed 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 underlying concept of this circuit centers on the utilization of DTMF technology for the remote control of household appliances such as lights and fans. In this setup, your phone serves as the source of DTMF signals through its built-in DTMF encoder, while the decoder function is handled by the HT9107B IC.
To facilitate the connection, a 1nf capacitor is incorporated into the mobile jack. This mobile jack consists of two wires, typically red and black. The decoder IC is interfaced with the red wire, while the black wire is grounded for proper functioning.
When a button on the phone keypad is pressed, it triggers the generation of a specific tone. This tone is subsequently decoded by the HT9107B IC and relayed to the ATMEGA8 controller. The ATMEGA8 controller then proceeds to process the received input and generates an appropriate output based on the pre-defined code it has been programmed with.
DTMF Controlled Home Automation System Circuit Diagram:
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 is equipped with an integrated operational amplifier, and the signal path proceeds as follows: the output of the op-amp is directed towards the pre-filters, which serve the purpose of segregating low and high frequencies. Subsequently, the signal is channeled through frequency and code detector circuits, leading to the latching of a 4-bit binary code.
To transfer the tone generated by the phone to the op-amp, a network of resistors and capacitors (100 kilo-Ohm and 1nf, respectively) is employed. Specifically, the non-inverting pin (Pin1) of the DTMF IC is connected to the Vref pin (Pin4), while the operational amplifier’s output (Pin3) is routed back to Pin 2 through a 100 kilo-Ohm resistor. Furthermore, a 3.579545 MHz crystal oscillator is linked to pins 7 and 8. Upon the detection of a DTMF tone, the 15th pin goes high; otherwise, it remains low. The steering circuit, comprising EST, RT/GT, a 10k resistor, and a capacitor, is responsible for the frequency detection and digitalization of the signal, with the decoded output emanating from pins 11 to 14.
Moving forward, the output pins of the DTMF IC (i.e., pins 11 to 14) establish connections with the PB0-PB3 pins of the controller. The controller’s output pins (PD0 and PD1) are, in turn, connected to a relay. This relay serves as a critical switch, isolating different segments of the circuit. In the context of this project, it enables the control of AC loads using the 5v signal originating from the controller. The specific type of relay employed in this setup is a magnetic relay.
How to Operate the Circuit?
Upon powering up the circuit, the controller commences a routine process of monitoring inputs. When the mobile keypad registers the number one being pressed, the decoder IC effectively translates the tone and produces a corresponding binary output of 1 (0001). This binary information is then relayed to the microcontroller, which subsequently triggers a high output at the PD0 pin. Connected to PD0, the relay plays a pivotal role in the circuit, leading to the activation of the fan.
Similarly, when the input received is the number 2, the fan is promptly deactivated. If the input is the number 3, it signifies the command to illuminate the light, while a received input of 4 signifies the command to switch off the light.
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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