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DATA CONSIDERATIONS
Once an RF link has been established, the challenge becomes how to effectively
transfer information across it. For simple control or status signals, such as button
presses or switch closures, consider using an encoder and decoder IC set.
These chips are available from several manufacturers including Linx, Microchip,
Holtek, and Motorola. These chips take care of all encoding, error checking, and
decoding functions. They generally provide a number of inputs to which switches
can be directly connected, and address or security bits to prevent unintentional
activation. These IC's are an excellent way to avoid protocol development and
bring basic remote control/status products quickly and inexpensively to market.
In most applications the modules will be interfaced to a microprocessor. A UART
may be employed or an output pin of the microprocessor "bit-banged" to create
a data stream. While many RF solutions impose complex formatting and
balancing requirements, the HP-3 series was designed to be as transparent as
possible. The HP-3 does not encode or packetize the data in any manner. This
transparency gives the designer tremendous flexibility in the structure of a
protocol. Of course the performance and reliability of the link are dependent on
the quality of external software and hardware. To properly apply the transmitter,
it is critical to understand the differences between a wired and a wireless
environment. At each point in the system there are timing and data-corruption
issues that should be understood and accounted for. The following section
provides a brief overview of these issues. You may also wish to read Application
note 161 (Considerations for Sending Data Using the HP-3 Series) prior to
beginning code development.
GND
ANT
CHS 0
CHS 1 SS CLOCK
CHS 2 SS DATA
CTS
POWER DOWN
VCC
GND/MODE
DATA IN
V
CC
V
CC
V
CC
Channel
Select
TX1
S1
3-Position
DIP Switch
R1
2.2K
3
16
+
+
+
+
C1
4.7 uF
C2
4.7 uF
C3
4.7 uF
12
1
3
4
5
6
15
8
J1
DB-9F
Serial
Connector
5
C4
4.7 uF
U1
Max 232
2
13
14
Figure 24: Typical Application: RS-232 Interface
GND
ANT
CHS 0
CHS 1 SS CLOCK
CHS 2 SS DATA
CTS
POWER DOWN
VCC
GND/MODE
DATA IN
D0
D1
D2
D3
DOUT
TE
OSC1
OSC2
GND
VCC
A7
A6
A5
A4
A3
A2
A1
A0
V
CC
Channel
Select
TX1
S1
3-Position
DIP Switch
R1
390K
S3
S4
D1
IN914
D2
S2
8-Position
DIP Switch
Address Select
Holtek
HT680
Figure 23: Typical Application: Remote-Control Transmitter