DESCRIPTION
time delay of 1 to 3 seconds, ensuring that the
sensor circuit must be continuously open for at
least 1 second before the D-24A will transmit.
This feature helps prevent activation from
short-term, spurious signals, and from signals
made from outside electromagnetic sources.
The transmitter may be re-triggered after a
30-second reset time. The transmitter has a
pushbutton for battery/transmission test.
NOTE: On the D-24A, the loop input terminals
must be closed for a minimum of 45 seconds
before the pushbutton will activate the
transmitter.
CODE SWITCH LOCATION
Use a pointed object (other than a pencil or pen)
to set the keys. The ON position is when the top
of the switch is down, facing the numbers. The
OFF position is when the top of the switch is up
and the bottom is down, away from the numbers.
In the example shown in Figure 3, keys 1,4,6
and 8 are ON; keys 2,3,5 and 7 are OFF.
The D-21A(/K), D-24A(/K), and D-26A(/K) are
digitally coded stationary radio transmitters
triggered by normally open (N/O) or normally
closed (N/C) sensors. These transmitters can
be programmed to activate any of Linear’s
standard digital receivers that are tuned to the
same frequency. Each transmitter can perform
many remote switching tasks and are typically
used in wireless/hardwire security systems.
Each unit is powered by a self-contained 9-volt
battery and can be connected to various
sensors with the built-in screw terminals.
The digital coding switch is attached to the circuit
board inside the case. To access the switch,
unsnap and slide off the back cover as shown in
Figure 1, exposing the battery, lead wire screw
terminals, and digital coding switch (see Figure 2).
Figure 1.
Removing
the
Transmitter
Back Cover
MOUNTING
SCREWS
8
7
6
NOTE: Transmitters with a /K model number
suffixareLinear’sCanadianmodelstunedto318
MHz. These instructions pertain to both the /K
and standard 303.875 MHz U.S. models.
D-26A N/O TIME-DELAY TRANSMITTER
5
4
3
The D-26A is used with various types of security
sensors that are normally open. The
special-purpose D-26A transmitter has a built-in
exit/entry time delay. The timer starts when the
sensor circuit closes. It begins a 5 to 10 second
countdown. If no action is taken before the time
delay is completed, the transmitter will send an
alarm signal to its companion receiver. Pressing
the pushbutton before the time delay period
has elapsed will prevent signal transmission.
In addition to canceling time-delayed signal
transmission, the pushbutton is used to test the
battery. Pressing the button turns on the red
LED if the battery is in good condition. The LED
does not light upon transmission.
1
RECESSED
WIRING
HOLE
O
N
CODING
SWITCH
O
F
F
SURFACE
WIRING
SLOT
D-21A N/O TRANSMITTER
The D-21A is used with various types of security
sensors that are normally open (magnetic
contacts, security floor mats, etc.). The D-21A
transmits a signal when the sensor circuit
closes. The transmitter triggers instantly, and
may be re-triggered after a 30-second reset time.
A pushbutton is provided for battery/transmission
test. Pressing the pushbutton with the sensor
circuit open (after the 30-second reset) triggers
the transmitter and turns on the red LED if the
battery is above 7.5 volts.
Figure 2.
Transmitter
Components
9-VOLT
BATTERY
Figure 3. Example
Coding Switch
Figure 4. Transmitter
Back Cover Mounting
SCREW
TERMINALS
INSTALLATION
To mount the transmitter, proceed as follows:
CODE SETTING
STEP 1: Select a location for the transmitter and
drive screws through the two countersunk holes of
the back cover to mount the cover (see Figure 4).
NOTE: Generally, the higher the transmitter is
mounted above ground level (minimum of 3
feet) the better the radio range should be.
STEP 2: For recessed switches with hidden
wiring, fish the sensor wires through the wire
access hole on the back cover. With surface
wiring, route the wire leads through the wire slot
on the back cover (see Figure 4).
CAUTION! All transmitters and receivers must be
re-coded by installer prior to operation. DO NOT
USE THE FACTORY SET CODE!
Among the 256 possible codes, four codes are
considered invalid, and should not be used. They
are: all keys ON, all keys OFF, and keys set
alternating ON/OFF or OFF/ON combinations.
To set a code, select any valid combination of
ON and OFF positions for the switch keys
numbered 1 through 8.
NOTE: The each transmitter contains a timing
circuit that allows a single transmission of a
2-second duration to occur, followed by a
30-second reset time. This means that regardless
ofthenumberoftimesthetransmitteristriggered,
itwillnotsendasignalmoreoftenthanonceevery
30 seconds.
D-24A N/C TRANSMITTER
The D-24A is used with various types of security
sensors that are normally closed (magnetic
contacts, security window screens, etc.). The
D-24A transmits a signal when the sensor
circuit opens. The transmitter incorporates a
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