Circuit Concept and Working
DTMF controlled home appliances project works over mobile DTMF technology that exists in Dial tone. DTMF stands for Dual Tone Multiple Frequency. There are some frequencies that we used to create DTMF tone. In simple words by adding or mixing two or more frequencies generates DTMF tone. These frequencies are given below:
In Given figure we can see two groups of different frequencies. When one upper and one lower frequencies mixed then a tone is created that tone we calls Dual Tone Multiple Frequency. In this project we control ac appliances by pressing dial pad keys like 1, 2, 3, 4, 5 and more.
Here we have connected a cell phone using aux wire to the DTMF decoder circuit. Before explaining the further working of project we need to know about the output of DTMF decoder for every key pressed.
In circuit diagram at K1, K2, K3 and K4 are 4 relays connected to the output of DTMF Decoder IC MT8870. Now when we press key 1 at the dial pad of mobile phone DTMF decodes this tone and generates a digital output given in table. Now According to given output in table Q1 is HIGH and Q1 is connected with Relay K1 which is turned ON. Similarly we can switch ON relays K2, K3, K4 by pressing 2, 4 and 8 keys respectively. Please refer the video for complete demo and assembly.
Components required :
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