©1999 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 2/4/03
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tions are just the opposite.
(See The-
ory of Operation for reason why.)
The
A latch normally is used for autopatch
operation. It has toll call restriction
circuitry connected to it. If used for
some other function, the toll call re-
strictor can be eliminated by simply
breaking the pc traces to pins 8 and 9
of U3, and reconnecting those inputs
to ground instead.
Any of the functions not required
to turn a latch on and off may be used
for some momentary purpose. Be-
cause the E functions are momentary
only, they should be considered first
for momentary applications.
The latching outputs can be used
to drive solid state circuits directly
and can drive small relays to switch
power loads. The output transistors
can sink loads up to +15V and 50 mA.
If you drive an inductive load, like a
relay coil, be sure to connect a diode
with reverse polarity across the load
to absorb any inductive spikes which
could damage the transistor.
The momentary outputs are essen-
tially the outputs of CMOS gates.
They provide about +5V in the active
state and close to ground in the pas-
sive state. Output current is no more
than 3 mA.
When you select programming
codes, you can use any touch tone
digit for any function you want. You
can reuse digits as many times as you
want; there is no need to use each
digit only once. The fan-out capabili-
ties of U2 allow it to drive any number
of AND-gate inputs from any digit
output pad. The mechanics of making
connections are more of a limitation.
The board uses wire jumpers for pro-
gramming. This allows easy field pro-
gramming without prom burners, etc.,
but it does require a little planning
and workmanship. If you analyze the
sample programming in Table 1, you
will see that it provides for maximum
use of all the digits with nearby func-
tion pads to make wiring neat. Any
codes can be programmed, though,
and if neatness and ease of program-
ming are not important to you, then
you have more freedom in selecting
codes.
Programming is done by soldering
2-1/2 inch lengths of hookup wire
stripped about 1/4 inch on each end.
That length allows a little slack so
wires can be moved around to allow
access to solder other wires.
Be sure to terminate the inputs to
all the AND-gates by connecting any
unused function programming pads
(not the digit output pads, but the
AND-gate input pads) to ground. If
the gate inputs are left floating, the
operation of the ic's can be erratic and
can affect other functions that are
used. Noise input can also cause
unterminated ic's to draw more cur-
rent.
Normally, the three digit "key" is
used as the first part of any com-
mand, and the fourth digit indicates
the function. However, if the security
is not needed and you don't mind hav-
ing someone accidently perform a con-
trol function by hitting one digit, the
pc board can be modified to provide
single-digit operation of one or more
functions. An example of this is that
some repeater owners want to be able
to turn off the autopatch with a single
digit, such as "#", even though the full
four digits are required to turn it on.
Also, in an industrial control opera-
tion, you might want to have quick
commands to perform repeated opera-
tions without having to dial up a "key"
sequence each time. Bear in mind
that the "key" provides useful func-
tions; so consider what you are giving
up before you make a decision to opt
for a single digit command.
Unfortunately, the only way the pc
board could be laid out was to put the
"key" bus trace on the top of the
board. This means, you may need to
modify the traces under the ic sockets
for U7, U9, or U11 to change to single
digit operation, depending on whether
you only want to change an individual
function, a group of functions, or all
the functions to single-digit operation.
If you compare the schematic diagram
with the pc board, you will note the
"key" bus pc trace running on the top
of the board from U6 at its lower-left
extreme to U11 at its upper-right ex-
treme and making a right-angle turn
just below the lower-right program-
ming pad.
The AND-gate pad(s) you wish to
reprogram for single digit operation
must be disconnected from the "key"
bus by cutting the pc trace, and such
pad(s) must be reconnected by a bus
wire jumper to +5V in-
stead, which you can
access on pin 14 of each
4081 ic. The jumpers, of
course, can be soldered
under the board, but
you must have access to
break the "key" bus on
the top of the board. If
you have a unit which is
already wired, you may
need to carefully unsol-
der the ic socket for nec-
essary access. If you are
reprogramming more
that one function, you
may be able to break
and reconnect a whole section of the
"key" bus instead of individual ic pins.
You may reduce the number of dig-
its in the "key" by reconnecting U5
and U6 latch inputs. For a 2-digit key,
disconnect 3rd digit key latch, U6B,
"D" input from U5B and connect U6
pin 9 to +5V instead. Then, use the
K1 and K3 programming pads as your
"key" inputs. U5B essentially is out of
the circuit.
If you want a 1-digit "key", then
disconnect the "key" bus line from
U6B pin 13 and connect it to U5A pin
1 instead. Use K1 as your "key" input
for programming.
Here is a trick suggested by a cus-
tomer on how to convert to a one-digit
key after the board has been assem-
bled using the 4 digit method. Re-
move U6, bend pin 13 out, and re-
install U6 making sure pin 13 does
not connect with pin 13 on the IC
socket. Now jumper pin 13 and pin
14 of U6 by soldering the pins to-
gether on the bottom of the board.
TESTING PROGRAMMED
BOARD.
After the board has been pro-
grammed, all of the functions may be
tested. Power up the board as done
for
Initial Testing
on page 2; apply
touch tones of proper level; and check
for proper responses at the momen-
tary and latching outputs with a volt-
meter. You can also monitor the "key"
bus line on the board with a voltmeter
to see that it goes hi for about five
seconds after the 3-digit key is sent
and then returns to lo. The "mute"
output can be checked at pad 3 at the
left side of the board to see that it
goes hi whenever any valid digit is re-
ceived.
You can also check the toll call re-
strictor circuit by attempting to dial
various numbers after the autopatch
latch is turned on. If you dial a 0 or 1
as the first digit after the patch is
brought up, the patch latch should
Table 1. Typical Programming Plan.
ProgramPads
Function _ Full
Sequence
*---K1
"Key" 1st digit
1---K2
"Key" 2nd digit
2---K3
"Key"
3rd
digit
0---R0
Repeater Off
* 1 2 0
9---R1
Repeater On
* 1 2 9
#---A0
Autopatch Off
* 1 2 #
3---A1
Autopatch On
* 1 2 3
8---B0
Aux B Off
* 1 2 8
7---B1
Aux B On
* 1 2 7
5---C0
Aux C Off
* 1 2 5
6---C1
Aux C On
* 1 2 6
B---D0
Aux D Off
* 1 2 B
A---D1
Aux D On
* 1 2 A
D---E0
Aux E0 Momentary Only * 1 2 D
C---E1
Aux E1 Momentary Only * 1 2 C