Hamtronics Td-2 User manual

GENERAL DESCRIPTION.

The TD-2 is an advanced DTMF

tone decoder and multichannel con-

troller providing 5 latching outputs

and up to 12 momentary outputs.

Latching outputs are handy to control

autopatches, repeaters, sub-audible

tone decoders, and various other

on/off functions. A toll call restrictor

is included in the autopatch control

circuitry at no extra cost. The heart of

the TD-2 is a central office grade, 16-

digit, crystal controlled DTMF decoder

chip with built-in filters to prevent

falsing on noise or voice signals. Reli-

able operation is maintained for any

audio input level from 100mV to 2V p-

p. Low power consumption is made

possible by the exclusive use of CMOS

ic's. The unit can operate on 10-

15Vdc at only 15mA. Control codes

are easily programmable and allow

flexibility in code types. See our cata-

log for a full list of features.

THEORY OF OPERATION.

Refer to schematic diagram. The

input to tone decoder chip U1 is proc-

essed through a dial tone filter and a

bandsplit filter using switched capaci-

tor technology. The signal is then

analyzed by two zero-crossing detec-

tors and a digital detection algorithm

to determine if and which tones are

present. Then, the resulting logic sig-

nals are processed in a code converter

and latch circuit to provide four bi-

nary outputs (called Q1-Q4) with en-

coded information about dtmf digits

which may have been received.

A valid digit strobe (StD) signal in-

dicates when any valid digit tones are

received. This valid digit signal is

used to gate U2 and to provide a mut-

ing signal to the autopatch board

when tones are received. It also oper-

ates the toll call restrictor, which is

discussed later. The whole circuit is

run on a clock controlled by color

burst crystal Y1. The audio input

signal is filtered by L1/C1 to remove

any rf which may be picked up on the

wiring. The ratio of R2-R3 sets the

gain of the op-amp input circuit. C3-

R4 sets the length of time necessary

for presence of valid tones and the in-

terval between tones to prevent erratic

operation. U2 decodes the hexadeci-

mal information from U1 to provide 16

CMOS output lines corresponding to

the digits on a DTMF pad. Program-

ming for the various functions is done

by soldering jumper wires from pro-

gram pads at the output of U2 to ad-

jacent function program pads.

The 4013 latches may be operated

synchronously or directly. The Q out-

put will assume a hi whenever the set

input is triggered by a hi or a lo when-

ever the reset input is triggered by a

hi. The not-Q output is just the in-

verse. The latch also may be operated

synchronously, with its Q output as-

suming the whatever state the data

input has applied when the clock in-

put receives a hi. If the clock input is

lo, the latch ignores the data input.

But if the clock goes hi at any time,

the latch will follow the data input

when the clock is hi.

U5A/B and U6B are D-type flip-

flops operating as a "key" latch in con-

junction with program inputs K1-K3.

The output of U6B is high only upon

proper receipt of a three digit code,

which provides a security "key" to

unlock the rest of the logic gates.

R8/C11/CR2 in the reset circuit of

U5A provides a five-second time delay.

When the first digit of the key is re-

ceived, the not-Q output of U5A re-

leases the reset inputs of the other

two flip-flops for about five seconds. If

the full three digit code is not com-

pleted within that time period, all

three flip-flops are reset.

There are 12 momentary functions,

each using a 4081 ANDgate. Nor-

mally, one input of each AND-gate is

tied to the so-called "key" bus coming

from U6B and the other input is tied

to a programming pad bearing the

name of the output line from the AND-

gate. To actuate a function, it is nec-

essary to send the three-digit key plus

a fourth digit indicating the desired

function. During the interval when

the key is active (about five seconds),

if any other function is selected, it

may be activated with just its one digit

function code. If the key period ex-

pires, then the key must be re-sent to

start another command. It is also

possible to eliminate the key alto-

gether, if the security is not needed,

allowing one digit commands at any

time. This is done by disconnecting

the input of the AND-gate normally

connected to the key bus and recon-

necting it to the +5V bus instead. You

can even use the key for some func-

tions and not others; using only a "#",

for instance, to turn off the autopatch,

but requiring the full four digits to

turn it on.

When a particular AND-gate re-

ceives both a key input and a function

input, it applies a hi signal to its out-

put line. In the case of five pairs of

AND-gates, the outputs also are tied

to the "set" and "reset" inputs of

latches. The latches, in turn, drive

output transistors and led's. The

open-collector transistor switches may

be used to drive external circuits.

Thus, the momentary outputs, which

are CMOS hi's in the active state, may

be used or the latch outputs may be

used or any combination of latch and

momentary outputs may be used as

desired.

The names of the lines were se-

lected based on two parameters.

First, the letter indicates the function

usually associated with the line. The

"R" function normally is used to en-

able or disable a repeater. The "A"

function normally controls an auto-

patch in a repeater. Of course, the

circuits can be used for any other

function, but it was thought best to

select names based on uses most

owners will have for them. The other

functions are not dedicated to any

particular function; so they were

named B, C, D, and E. (E is the pair

of momentary functions which has no

latch. We loaded the pc board with all

the functions we could fit on the

board, and we had two AND-gates left

to provide the extra momentary func-

tions. There is no other significance.

If you need a momentary function or

two, you can use the E functions

without feeling you are wasting an as-

sociated latch.) The number, 1 or 0,

indicates which line turns the latched

output on or off.

It is a little confusing looking at

the latch circuits until you realize that

the repeater latch circuit is different

from the others, which turn on a cir-

cuit by the collector of the transistor

conducting to ground. The R latch

mutes a repeater by grounding the

COS line from the receiver or auto-

patch to the COR board input. Thus,

the repeater is off when the transistor

is active instead of being on when the

transistor conducts like the other cir-

cuits. The autopatch latch is differ-

ent, too, because of extra toll call

restriction circuits. There also is a

difference in the way that the latches

are preset at power up. The repeater

wants to be enabled after a power

failure, not disabled. So its latch is

wired to default with the repeater en-

abled. The other latches default in

the off condition. Default status is

set by the C/R networks on the clock

or reset inputs of the latches. When

power is first applied, a positive pulse

is applied by the capacitor to reset the

HAMTRONICS

TD-2 DTMF DECODER/CONTROLLER

latches.

The autopatch latch has some ex-

tra circuitry with it to provide toll call

restriction. U4 is a counter which

keeps track of which digit is received

after the autopatch latch is turned on.

When the autopatch is off, the not-Q

output of U6A is hi, keeping U4A/B

reset. However, when the four digit

code is sent to bring up the patch,

U6A turns on, and the reset signal is

removed from U4, allowing it to count

digits. The Q output of U4B remains

lo until the second digit after the

autopatch turns on. If a 0 or 1 is re-

ceived during the first digit after the

patch is brought up, U3B, which is

used as an AND- gate, is satisfied that

it has two lo's, and it provides a clock

input to autopatch latch U6A. Since

the data input is wired lo, that causes

the output of the latch to assume the

data input (lo) condition, thereby kill-

ing the autopatch. If any other digit is

received as the first digit of a phone

number, U3B is not satisfied, and the

autopatch remains on. On subsequent

digits, digit counter U4 removes its lo

from U3B, so the patch will not be

turned off by any received digit, even a

0 or 1.

CONSTRUCTION.

The pc board is double-sided with

plated-through holes. Because it is

more difficult to unsolder from this

type of board, be sure parts are ori-

ented properly and of the correct

value before soldering. Pc traces are

close together, so use a fine soldering

iron tip.

During construction, orient the

board right side up as shown in the

parts location diagram. The top side

as shown has the pin number mark-

ings. Also refer to the parts list and

schematic diagram during construc-

tion.

Before assembly, it is important to

decide whether or not you will use the

three digit key for controlling all of the

functions. If you will want to control

some or all of the functions with only

a single digit code, it is necessary to

break some pc paths on the top of the

board which will be concealed later by

ic sockets. If you want to modify the

pc board in this way, refer to the sec-

tion on Programming prior to assem-

bly.

CAUTION. The CMOS ic's used in

this kit are all static sensitive; so han-

dle them with care. A grounded wrist

strap should be worn whenever you

pick up an ic. Do not open the pack-

ages containing the ic's until you are

ready to install them, and then handle

them only with suitable static control

measures.

a. Install ic sockets oriented with

notches as shown, and solder.

b. Install the led's on the board,

observing polarity. The positive lead

is longer on some led's. On others,

there is a flat on one side as shown on

the parts location diagram.

CAUTION: Small LED's are heat

sensitive. Keep the LED's up off the

board about 1/4 inch and solder

quickly, applying minimum heat to

avoid damage.

c. Install the remaining parts

other than the dip ic's, according to

the parts list. Be sure to observe po-

larity on the diodes, transistors, U12,

and the electrolytic capacitors. Verti-

cally mounted parts are illustrated

with a circle indicating the body of the

part, and the diode symbol next to

CR2 on the diagram indicates the po-

larity.

d. Check over construction to be

sure all parts are installed in proper

places and with proper polarity and

that solder connections are good.

Look for things like cold solder joints

and solder splashes. Note that one

hole above U5 is a "via" used only to

make a connection between the top

and bottom of the board. Nothing is

installed in this hole. Note also that

programming wires will be installed

later.

e. Using static protection de-

scribed earlier, carefully unpack the

dip ic's and install them in the sock-

ets. Be sure to orient them as shown,

according to either dot or notch on the

end of each ic. If any conflict between

notches and dots on an ic, the notch

(which only appears on one end) takes

precedence. Sometimes, RCA cmos

ic's have a test dot of some color (eg.

blue) on one end, and such dots can

be confusing because they can appear

on either end. Ignore such dots if the

ic also has a notch or white bar on

one end, which would indicate the pin

1 end. Be careful to engage all the

pins in the socket; don't let any leads

bend over.

PC BOARD HANDLING PRE-

CAUTION.

Be careful whenever you handle

the module. Even though static dam-

age 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.

INITIAL TESTING.

Although it is not necessary, you

may wish to test the tone decoder por-

tion of the board before you proceed

with programming. To do so, connect

a power supply ground to the ground

trace at one of the four corners of the

board, and connect +10 to +15 Vdc to

the dc input at pad 2. Connect a

source of touch tones to audio input

pad 1, with a level between 100 mV

and 2V p-p. The outputs at the left

two rows of programming pads should

have a CMOS logic level (close to 0

and +5V) with the hi corresponding to

reception of a valid touch tone digit.

The "mute" signal should also appear

at mute pad 3 at the edge of the board

whenever any valid digit is received.

PROGRAMMING.

The following discussion is an at-

tempt to simplify the steps required to

plan how to use the various functions

on the TD-2 module. There are many

variables involved, but breaking it

down like this should make it easier

to consider everything.

Read through the paragraphs

which follow, and take actions where

appropriate. Table 1 is a sample of the

type of plan you should make. This is

a typical setup in an amateur radio

repeater installation, and it is the pro-

gramming we use for wired units at

the factory unless something else is

requested. The chart shows the corre-

spondence of the decoder output pads

with the function-input programming

pads for each function. It also shows

the complete command sequence de-

sired for each function, based on hav-

ing to send the three "key" digits plus

the function-indicator digit for each

command. You should make a plan

like this for your installation, noting

what each function will be used for.

There are 12 momentary functions

available. 10 of them may be used ei-

ther for a simple momentary function

or as the input to control a latching

function. The E0 and E1 functions

may be used only as momentary func-

tions. (Refer to theory of operation for

more information on these circuits.)

The five latching functions are

similar except that the R function, be-

ing normally used for control of a re-

peater, has reversed nomenclature,

ie., the "R0" function causes a short to

ground at the latch transistor output

pin, and the "R1" function causes an

open circuit. The other latching func-

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

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. Solid S tate R e la y

Wiring.

Figure 3B . S mall Re lay

Switching Power Contactor.

Contactor

Coil

12Vdc

Output of

TD-2 Xstr

Common

C Hot

12Vdc

–

To AC Load

AC In

AC Out

C Hot

Output of

TD-2 Xstr AC

Common

common "key" used with all com-

mands, and the fourth digit being a

function identifier. As soon as the

fourth digit is received, the selected

function is performed.

If some or all of the functions have

been modified for operation with a

smaller "key" or no "key" at all, then

operation will be different for those

functions. For security, the entire

command sequence must be sent

within about five seconds or a timer

will reset and the sequence must be

started from scratch.

Note that the "key" timer will keep

the key circuit enabled for about five

seconds once it is tripped. Therefore,

if more than one command is to be

sent in a short period of time, only the

final digit of the second and following

commands need be sent. If you re-

send the "key" digits during the five

second period, they will be taken as

function identifier digits and not "key"

digits and may cause erroneous op-

eration.

For example, using the commands

in our example, Table 1, if we want to

turn the autopatch on and then off

again within the five seconds, we

would send "* 1 2 3" to turn it on and

just "#" to turn it off, since the "* 1 2"

is still "in memory", so to speak be-

cause the "key" timer is still on.

TROUBLESHOOTING.

Tracking down trouble is fairly

straightforward. The Theory of Opera-

tion section describes the signal path

and what each circuit does. The only

significant voltages are CMOS hi's

(near +5V) and lo's (near ground) as

marked on the schematic by thelittle

pulse symbols. The only exception is

the latch output transistors, which

have about +0.7V at the base when

turned on. The collector is at ground

when conducting and open circuited

when off.

The operating voltage of the unit is

+10 to +15Vdc. Current drain nor-

mally is about 15mA, depending on

how many led's are lit, since they

draw more current than the other cir-

cuits.

Note that led brightness may vary

from one led to the next. To save

power and space on the board, the

led's are driven directly by the CMOS

ic's. In this mode, the ic's put out just

as much current as they can into

what looks like almost a short circuit

load. The amount of short-circuit

current varies from one chip to the

next, and so the brightness of the

led's vary. This should cause no con-

cern, since the function of the led is

simply to indicate whether the circuit

is on or off.

A logical troubleshooting proce-

dure would be to start by checking the

audio source to be sure valid tones of

proper level are being fed into the TD-

2. The range of acceptable levels is

100 mV to 2V peak-peak. Table 2

gives frequencies of touch tones. You

should check your tone pad if some of

the digits don't respond, to see if the

pad is sending tones on frequency. If

the U1 chip is not decoding touch

tones, check to see if its oscillator is

running and at the proper frequency.

You may need to use a 10:1 scope

probe for the frequency counter input

to keep from loading the oscillator cir-

cuit. The next step would be to check

the hexidecimal signals from U1 to U2

and check for a valid digit signal from

pin 15 of U1 (the valid digit led should

light).

Remember that the ic's are static

sensitive. You don't want to further

damage the board while troubleshoot-

ing. A ground wrist strap should be

worn when handling the ic's.

The next thing to check is the "key"

bus. Check to see if the output of

U6B at pin 13 goes hi when the "key"

digits are received. Next, check the

momentary outputs: R0, R1, A0, A1,

etc. Finally, check the 4013 latches to

see if they are responding and supply-

ing the required current to turn on the

output transistors. The led's can be

used as an indicator of latch status.

If falsing occurs with some com-

mands or the unit fails to respond,

you should check the twist of the in-

coming tones in addition to their fre-

quencies. Twist is the relationship

between the level of tones in the high

group to the level of tones in the low

group. There should be no more than

10 dB difference between the two tone

levels in any digit. That is about a 3:1

difference in voltage. Various factors

influence the twist of the tones, in-

cluding the tone pad at the transmit-

ter, coupling capacitor values in your

system, receiver de-emphasis, trans-

mitter pre-emphasis, and how hard

you drive the tones at the transmitter.

One problem with some transmitter

setups is that a ham will set his tone

level too high, trying to get full 5 kHz

deviation. The level is actually set so

high as to go into limiting. This may

cause the high and low tones to be

transmitted at the same level instead

of having the desired pre-emphasis. It

may also add distortion to the tones.

Then the receiver de-emphasis at the

other end causes the low tone to be at

a higher level than the high tone be-

cause the pre-emphasis at the trans-

mitter was wrong. You should

encourage system users to be conser-

vative in setting tone levels at their

transmitters.

Another cause of bad twist on

touch tones can inadvertently occur if

a sub-audible tone decoder is used in

the receiving system. The high-pass

filters supplied on sub-audible tone

decoder boards, usually connected in

series with the audio in the receiver to

get rid of buzz from sub-audible tones,

can severely degrade the levels of

lower frequency touch tones as well.

If you have such a board installed in

your receiver audio path, you might

want to check its effect on touch tone

twist. If a problem, you may want to

take your touch tones from a point in

the receiver unaffected by the high-

pass filter or even just not use the fil-

ter in your6 receiver. Generally, the

required level of deviation to make a

sub-audible tone system work is very

low, about 0.2 KHz or less, and some

people run the level much higher than

needed, which causes the buzz. Run-

ning the proper level may allow the fil-

ter to be removed with no great

problem.

ested Selective Callin

Unit Ci

cuitr

CUSTOMIZING.

There are several parameters

which are preset to what is considered

normal, but you may wish to change

them if settings don't do what you

want.

The first is the duration of tone

presence necessary to be recognized

as a valid digit. This is set, along with

minimum time required between dig-

its, by R4/C3. The present setting is

what is considered normal in the tele-

phone industry, namely 40-50 mSec.

You may wish to change it so you can

dial faster (but with possible falsing)

or slower (for more protection).

Another parameter you can play

with is the five second timer setting

for the window after reception of the

"key" digits during which other tones

will be accepted as function indica-

tors. This is set by the R8/C11 time

constant. You could shorten the time

experimentally to find a time which

requires someone to really send the

four digits quickly and allow no addi-

tional time to do other commands. Or

you could slow it down so that it

would allow a series of commands to

be sent with one digit each after the

initial "key" digits are sent.

The gain of the input op-amp in U1

can be changed within reason to allow

various ranges of audio levels to be

accepted. The gain is set by the ratio

of R3/R2.

SOME ADDITIONAL TRICKS

Popular Media Converter manuals by other brands

Clear View Audio

Clear View Audio KR425H-16 user manual

Honeywell

Honeywell HUSS-E1 manual

Antelope

Antelope Zodiac+ owner's manual

Analog way

Analog way DPH104 quick start guide

TP-Link

TP-Link TL-FC311 manual

DRAKE

DRAKE DDC864 manual

YBA DESIGN

YBA DESIGN Heritage D100 owner's manual

Digiflex

Digiflex CM430S Installer's reference guide

Syscom Video

Syscom Video 8CH FX-TRON instruction manual

Beijer Electronics

Beijer Electronics BoX2 base v2 Configuration manual

AV TOOL

AV TOOL AVT-3310 instruction manual

MOOD

MOOD ProFusion iO Pandora quick start guide

Westermo

Westermo LD-63B DC installation manual

Rotel

Rotel RDD-1580 technical information

Gefen

Gefen EXT-DVIKVM-LAN user manual

Crestron

Crestron HD-CONV-USB-300 quick start

Sealey

Sealey SA501 quick start guide

CTS

CTS MCT-3002 Series user guide

HAMTRONICS TD-2 User manual

Popular Media Converter manuals by other brands