©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 2/4/03
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dump. It should not dump if any
other digit is sent first or if a 0 or 1 is
sent after the first digit in the phone
number.
INSTALLATION.
Caution
. Be careful whenever you
handle the module. Even though static
damage occurs most easily before ic's
are installed in their sockets, damage
can still occur to the ic's in a completed
module if a static discharge occurs at
any part of the board during handling.
Although wrist straps are not abso-
lutely necessary just to handle the
completed board, you should make it a
habit of discharging your hand to a
grounded object before touching a
CMOS module.
Mounting.
The board should be mounted to
your chassis with 4-40 standoffs
about 3/8 inch long in the four cor-
ners of the board. Be sure to get a
good dc and signal ground through
the mounting hardware. If you can-
not get ground through the hardware
or if you need a ground lug to solder
to, you can mount a solder lug under
the mounting screw in one corner of
the board. Placement of the board is
not critical, but the board should not
be mounted in a strong rf field. In a
repeater, the transmitter already is
shielded; so usually, you don't need to
do anything special. In our REP-100
Repeater, the TD-2 normally is
mounted under the left side of the
chassis, toward the front.
Power.
The unit is designed to operate on
+10 to +15Vdc at about 15 mA. The
low power consumption is due to the
CMOS circuitry. A voltage regulator
on the board takes care of voltage
variations within the range specified,
but be sure you use filtered dc power
and don't allow any spikes or reverse
polarity to be applied.
Tone Inputs.
The range of audio tone levels
which the tone decoder ic will accept
is 100 mV to 2V peak-peak. Audio
can be applied from any source, in-
cluding radio receivers, and telephone
lines with some sort of interface such
as an autopatch board. The audio
source must be referenced to ground.
Check to be sure that your
source is compatible. If not,
some adjustment will have to be
made. If you cannot alter the
level from your source to within
this range, you may be able to
change the sensitivity of the
tone decoder to some extent.
The input circuit of U1 is a typical op-
amp, with gain set by the ratio of
R3/R2. A reasonable change in resis-
tor values can be made to reset the
range of levels the chip will accept.
If you interface with our AP-1
Autopatch Board, you don't need to be
concerned about compatibility. The
tones for the TD-2 should come from
E8 on the Autopatch Board.
Output Circuits.
The latch outputs are open-
collector transistor circuits, which can
be used to sink current up to 50 mA
on circuits up to +15V. The
Theory of
Operation
and
Programming
sections
tell more about the default condition
and control line terminology. If you
use the outputs to operate small re-
lays, be sure to put a reverse diode
across the relay coil to soak up tran-
sients.
The "R" latch output should be
used if you want to enable and disable
a repeater by remote control. The "R"
output is normally used in our REP-
100 Repeater to ground the COS line
coming from the receiver or autopatch
to the COR board. This prevents the
transmitter from being keyed after the
"R0" command is given.
The "A" latch output should be
used to turn an autopatch on and off.
In our REP-100 Repeater, the "A" out-
put grounds E13 of the AP-1 Auto-
patch Board to turn on the autopatch.
The "Mute" output from pad 3
normally is connected to E10 on our
AP-1 Autopatch Board to mute the
transmitter audio whenever a valid
digit is received so that it cannot be
heard on the air.
Momentary outputs are direct
CMOS outputs from 4081 and-gates.
They provide close to +5V in the active
state and close to ground in the pas-
sive state. CMOS outputs will provide
only low current levels, up to about 3
mA.
Switching Large Loads.
In applications where the TD-2 is
used to turn equipment on and off,
the output transistor in the TD-2 can
be used to turn a relay on and off.
Two types of relays can be used.
Figure 3a shows a solid state relay,
such as the A95 relay we sell as an
accessory. The positive input of the
relay goes to +12Vdc and the negative
input goes to the TD-2 output. Note
that solid state relays generate heat;
so the metal base of the relay must be
coated with heatsink compound and
mounted to a metal box or other metal
object to dissipate the heat. The A95
relay is rated to switch ac current up
to 10A, at voltages of 24 to 220Vac.
The other type of setup is to use a
small relay, drawing less than 50mA,
to switch ac to operate a large power
contactor, as shown in figure 3b, or
used to switch a small load directly.
In this case, make sure you have a di-
ode connected as shown to prevent
damage from transients generated
when the relay coil is turned off.
LED Indicators.
There are led's on the board to in-
dicate the status of the various func-
tions: one for each latch and one to
indicate when a valid digit is received.
Although these were included primar-
ily for use in testing, it is possible to
remove them from the board and care-
fully extend them to a front panel with
hookup wire.
OPERATION.
Operation is fairly simple. A con-
trol sequence normally consists of
four digits, with the first three being a
Table 2. DTMF Frequencies
1209 Hz 1336 Hz
1477 Hz 1633 Hz
697 Hz
1
2
3
A
770 Hz
4
5
6
B
852 Hz
7
8
9
C
941 Hz
*
0
#
D
Figure 3 A. S olid S tate R e la y
Wiring.
Figure 3B . S m all R e la y
S witch ing P o we r C ontact or.
To
Contactor
Coil
+12Vdc
Output of
TD-2 Xstr
AC
Common
AC Hot
+
+12Vdc
–
To AC Load
AC In
AC Out
AC Hot
Output of
TD-2 Xstr
AC
Common