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ABSTRACT
Here is a microcontroller based wireless equipment controller that can switch on or off upto four devices at a desired time interval set by the user in the transmitter. The devices can be controlled remotely from a distance upto 30 metres from the transmitter. In the transmitter, an LCD module is used to show the device numbers and preset control time for the devices (00 to 99 seconds). The 8-bit AT89C51 microcontroller is the main controlling part of the transmitter section. It is connected to the LCD module, input switches and encoder IC (HT12E). The device control program is stored in the memory of the microcontroller to control the devices as per the time out settings done through input switches S1 through S4. The TRX -434 RF transmitter module uses a digital modulation technique called ASK (Amplitude Shift Keying) or on-off keying.
The RX-434 radio receiver module receives the ASK signal from TRX-434. The HT12D decoder demodulates the received address and data bits.
Concepts of wireless RF communication and automation with AT89C51 microcontroller are used here.
CHAPTER 1
INTRODUCTION
The system comprises a transmitter and a receiver as described belows
1.1 TRANSMITTER SECTION :
Fig.1.1 shows the block diagram of the transmitter section. Four push button switches (S1 through S4) are used as input to select the devices and sets the time out in the transmitter section. These are designated as up, down, enter and run keys respectively. The time out data is transferred over the RF wireless page link to the receiver section.
Fig. 1.1 –Block Diagram Of Transmitter Section For Wireless Equipment Control
The 8-bit AT89C51 microcontroller is the main controlling part of the transmitter section. It is connected to the LCD module, input switches and encoder IC (HT12E). The device control program is stored in the memory of the microcontroller to control the devices as per the time out settings done through input switches S1 through S4.
A two-line, 16 character LCD module shows the status of the main program that is running inside the microcontroller. The HT12E is an 18 pin DIP package encoder IC that encodes 4-bit data and sends it to the TRX -434 RF transmitter module.
The TRX -434 RF transmitter module uses a digital modulation technique called ASK (Amplitude Shift Keying) or on-off keying. In this technique, whenever logic ‘1’ is to be sent, it is modulated with carrier signal (434 MHz). This modulated signal is then transmitted through the antenna. The waveforms in fig. 2 depict the ASK concept.
Fig. 1.1.2 – ASK Concept For The RF Transmitter Module
1.2 RECEIVER SECTION :
Fig. 3 shows the block diagram of receiver section. The 12V DC supply, used along with the 5V regulator, can be provided by a 12V battery or power adaptor.
The RX-434 radio receiver module receives the ASK signal from TRX-434. The HT12D decoder demodulates the received address and data bits. IC CD4519 is a quadruple two-input multiplexer that selects appropriate data bits to control the devices. The ULN 2003 relay driver consists of seven npn darlington pairs that feature high- voltage outputs with common cathode clamps diodes for switching the inductive loads. The collector –current rating of a single darlington pair is 500 mA.
Fig. 1.2 –Block Diagram Of Receiver Section For Wireless Equipment Control
1.3 APPLICATIONS :
1) Used for controlling home appliances.
2) Used for controlling industrial instrumentation.
3) Used for controlling devices in labs