Remote control transmitter uses AT89C2051 microcontroller to transmit the codes according to the key pressed key codes are output from the pin number 3 of the microcontroller and connected to the data in pin of the 433MHZ radio transmitter module which transmit the codes to air.
Transmitter circuit explanation: eight keys are connected in four by two matrix to the microcontroller ic1 at2051. Key data is transmitted through the 433 mhz transmitter module through its pin no 3 of the microcontroller which is tx pin of the in built uart of the microcontroller and works on 1200bits/sec.Crystal X1 along with capacitor c4 and c5 gives the required clock input to the microcontroller. C 3 and R1 forms the reset circuitory connected to pin no 1 of the microcontroller. Key pressed value is transmitted through antenna Ascii codes are transmitted from the transmitter part.
433MHZ radio receiver module receives the codes from the attached antenna and data is in from pin 7 of module serially. This data is given to the rx data in pin of the microcontroller on the receiver pin 2 of the microcontroller ,relays are switched ON OR OFF .
Relay on off action is a toggle action when same codes are received second time .the relay is previously on it will become off or vice versa.Transister Q1 to Q16 forms the relay driver circuit.and drives 12v relay . output of the normally open contacts can be used to switch on devices of your choice .
Relay contact capacity is only 7 ampere avoid overloading .9v 1 ampere transformer is connected to PCON1 power connector diode d1 to d4 forms bridge rectifier circuit, c1 to c4 are filter capacitors ic1 is 5v regulator ic out put of this ic is 5v regulated power supply required to drive our microcontroller and other ics.Input of the regulator is 12v dc which is also used for driving the relays.
Capacitor C5 and r2 gives the required reset pulse to microcontroller.capacitor c6,c7 along with the crystal x1gives the clock pulse to microcontroller.Resistance connected to the base of the transistors (r3to r10) are current limiting restances. SIL ARRAY resistance network of 10×8 are connected to pin 12 to 19 of the microcontroller to provide pullp(high) to these pins. D5 to d12 connected across relay coil are to protect the circuit from the back e.m.f. generated by the relay coils .RL1 to RL8 are relays.
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