5. The RF Transmitter 2:
The rf transmitter 2 is the same unit that was explained in the previous sections. It transmits the serial data from the encoder to the remote control and command unit.
6. The Relay Based Mains Switching Section:
As the devices that are to be switched on are of course going to be ac operated. Thus some form of ac switching arrangement would be required. This has been realized in the project with the help of four electromagnetic relays. The use of relays ensures sufficient isolation between the dc control circuit and the ac load that is being switched. The relays used here are 12V pcb mount type having a resistance between 150 to 200 ohms which would thus require about 65mA of current to drive it. The loads are connected to the normally open contacts of the relay so that the devices will be switched on when the relays are energized.
The status display and key pad section: this section lets the user see the status of the remote loads that are connected to the base unit. As explained earlier, the status is sent from the base unit to the command and control unit by the encoder 2– rf transmitter2-rf receiver2-decoder 2 link.
The status display LEDs have been directly connected to the output of decoder 2 as it capable of driving the LEDs directly. The decoder itself also drives the warning buzzer via a driver. This buzzer would start buzzing whenever the VT signals from the decoder disappears indicating a break in the rf link.
The key pad has only four switches, one for each load to be controlled. Of course by the merit of four data lines that the encoder has it is easily possible to control 16 loads without much alteration in the hardware. The switches are directly connected to the data input lines of the encoder 1.