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 4:16 DECODER (IC 74154) :

A decoder is a device which does the reverse operation of an encoder, undoing the encoding so that the original information can be retrieved. IC 74154 is an active-low output decoder i.e, a LOW at output signifies active output while a HIGH signifies undesired output.

 

It takes the 4-bit input from DTMF Decoder at its Pins 20 to 23. It decodes the 4-bit input to 16-bit output and reveals the output at Pins 1 to 11, 13 to 17.

In our project, we utilized outputs at Pins 1 to 6. These output (6-bit) is fed to NOT gate IC as the IC74154 is an active-low output IC.

Pins 12,18,19 are grounded while Pin 24 is connected to Vcc.