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“The basic is very simple… You need a bluetooth enable host device i.e. mobile,computer or anything!! For the sending of command to the circuit. We have used a bluetooth module(HC-05 “HANDS & LEGS OF THE CIRCUIT” ) for catching the signal from paired host device and relaying the same to the microcontroller through its Tx pin to TxD of the later. But you can also use HC-06/07, Sable-x-R2, TIWI-uB1 etc. Now comes the microcontroller…”HEART & BARIN OF THE CIRCUIT”… receives data from bluetooth module and does the work according to the code written in it and REPLIES to the bluetooth module.(TxD to Rx) Pins of microcontroller gives output and thus connected pins of ULN2003 receives it and gives 0V(initially 5V) making the relay trip(work). Relay’s one leg connected to 5V(OR 6V) and another leg get 5V or 0V depending on ULN2003 output. When potential difference(voltage) across relay is 6V it works for 0-3V it doesn’t work.”

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