Linx Technologies CMD-HHTX-xxx - Manual (Page 2)

Page 2 Page 3
THEORY OF OPERATION
The CMD-HHTX-*** OEM Handheld transmitter combines the LC Series
transmitter and Splatch planar antenna with an on-board Holtek HT640 encoder
IC to form a simple, yet highly reliable, RF remote-control transmitter. The LR
Series transmitter is a low-cost, SAW-based ASK / OOK transmitter.
When a button is pressed on the transmitter, power is applied to the internal
circuitry and the encoder IC is enabled. The encoder detects the logic states of
the address lines and button data lines. These states are formatted into a three-
word transmission cycle that continues until the button is released. The encoder
data is used to modulate the transmitter, which, through the antenna, conveys
the data into free space. On the receiver side, a decoder IC or custom
microcontroller is used to check the transmitter’s address bits against the
address settings of the receiving device. If a match is confirmed, the decoder’s
outputs are set to replicate the transmitter’s button states. These outputs can
then be used to activate external circuitry required by the application.
The transmitter is compatible with several Linx receiver products, including the
LR, KH2, LT, and OEM product families. For applications where range is critical,
the LR Series receiver is the best choice due to its outstanding sensitivity. When
the transmitter is combined with an LR Series receiver and the HT658 decoder
chip, ranges of up to 1,000 feet are possible. Applications operating over shorter
distances will also benefit from the increased link reliability and superior noise
immunity provided by the LR Series receiver.
1. Characterized, but not tested
Notes
ELECTRICAL SPECIFICATIONS
Parameter Designation Min. Typical Max. Units Notes
POWER SUPPLY
Operating Voltage V
CC
2.1 3.0 3.6 VDC –
Supply Current I
CC
– 3.4 – mA –
Power-Down Current I PDN – 5.0 – nA 1
TRANSMITTER SECTION
Transmit Frequency Range: F
C
CMD-HHTX-315 – 315 – MHz –
CMD-HHTX-418 – 418 – MHz –
CMD-HHTX-433 – 433.92 – MHz –
Center Frequency Accuracy – -50 – +50 kHz –
ENVIRONMENTAL
Operating Temperature Range – -30 – +70 °C 1
SETTING THE TRANSMITTER ADDRESS
The OEM Handheld transmitter allows
the selection of one of 256 unique
addresses. All transmitters are supplied
set to the same address. To avoid
contention with other units or to create
unique relationships, the address can
be changed. This is accomplished using
internal DIP switches as shown. The
switches are accessed by removing the
rear cover as for battery replacement.
If the switch is on, the address line is
connected to ground, otherwise it is
floating. The receiver’s address must
match exactly in order for the units to communicate. Application Note AN-00300
describes in detail how to set the address to match any of the receivers offered
by Linx. This note can be found in the Support section of the Linx web site,
www.linxtechnologies.com.
CMD-HHTX BUTTON ASSIGNMENTS
This diagram illustrates the relationship between the button locations and
encoder data lines.
D7 D6
D5 D4
D3 D2
D1 D0
Figure 3: CMD-HHTX-*** Button Assignments
ON OFF
A7 = 1
A6 = 2
A5 = 3
A4 = 4
A3 = 5
A2 = 6
A1 = 7
A0 = 8
Figure 2: DIP Switch Assignments