TXE433
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4
THE TXE433
This wireless RF transmitter/encoder has a 4 bit data input that will be
transmitted and encoded, then decoded by the receiver, RXD433. The
output is CMOS compatible when the unit is run on +5 volts.
The “decoder address select” allows you to use one transmitter to control
different receivers by giving each receiver a unique address. The decoder
chip has eight address lines that can be connected to 5 volts or
ground, making it a simple matter of matching the address select pins on the
receiver/decoder module to match the address pins on the transmitter/
encoder. These outputs are also CMOS compatible when run on +5 volts.
The transmitter/encoder unit has a “transmit enable” input. When the
address pins are set up properly and you are ready to transmit, you must
ground the “transmit enable” pin to send the data to the receiver.
How Encoders and Decoders work:
A wireless remote control system requires a clean input signal to ensure that
correct data is received. At all RF frequencies, but especially at the
frequencies where unlicensed transmitter operation is allowed, the RF
spectrum is cluttered with signals and noise that must be filtered for proper
data reception. Rather than use microprocessors to detect and correct
errors, an encoder IC and corresponding decoder IC can be used on the
transmitter and receiver. A code is generated at the transmitter that must be
matched at the receiver before the data is recognized as being valid. This
type of system is widely used in wireless control applications since it is a
reliable way of ensuring security and eliminating interference. Your garage
door opener is an excellent example of such a system. All the openers on
your street may be made by the same company, and may even be on the
same frequency, but each has an internal code programmed into it so that
when you push the button, only your garage door opens.
In our TXE/RXD modules we use the Holtek HT12 series of ICs to
accomplish this encoding/decoding scheme. Following is an explanation of
how these IC‘s work.
Let’s explore how the data and address lines allow one to control many
different outputs for different applications. Because of the versatility of the
HT-12E encoder/decoder chips it is possible to program hundreds of
possible addresses and transmit to several different receivers using the
same transmitter. The HT12E encoders begin a 4-word transmission cycle
when transmit enable is pulled low. This cycle will repeat itself as long as
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