NHRC NHRC-2 User manual

NHRC-2 User Guide
NHRC-2 User Guide Page 1 2/28/2000
Copyright © 2000, NHRC LLC
All Rights Reserved.
NHRC-2 Repeater Controller
User Guide
Rev D PCB only
Contents
1. Installation
1. Electrical Connections
2. Adjusting the Audio Levels
3. Initializing the Controller
2. Programming
1. Controller Modes
2. Programming the Controller
1. Programming the Timers
2. Programming the CW Messages
3. Programming the Flag Bits
4. Recording the Voice Messages
3. Enabling/Disabling the Repeater
3. Operating
1. About the IDs
2. The Tail Message
3. Using the Tail Message as the Courtesy Tone
Index of Tables
• Configuration Flag Bits

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• Electrical Connections
• Message Commands
• Morse Code Character Encoding
• Programming Memory Map
• Timer Address and Resolution
Board Layout
1. Installation
1. Electrical Connections
The controller uses a female DB9 connector (P1) for all signals. It requires
receiver audio and a signal present indication (CAS) from the receiver, supplies
transmit audio and PTT to the transmitter, and requires 13.8 volts DC for power.
Be very careful when wiring DC power to the controller, reverse polarity will
destroy the ICs. The connector pinout is shown in the table below.

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Electrical Connections
Pin Use
1 Ground
2 +13.8 Volts
3 PTT (active low)
4 TX Audio
5 RX Audio
6CAS+
7CAS-
8 Ground/TX Audio Return
9 Ground/RX Audio Return
Receiver audio can typically be taken from the high side of the squelch control.
This audio must be de-emphasized with the controller's optional de-emphasis
circuit, which provides a -6dB/octave slope. Optionally, audio can be taken from
later in the receiver's audio chain, where it is already de-emphasized. Care must
be taken that this source of audio is not subject to adjustment by the radio's
volume control. If the receiver audio has not been properly de-emphasized, either
in the receiver itself or on the controller board, the repeater will have a very
"tinny", unnatural sound to it.
To de-emphasize the receiver audio on the controller board, install a 0.0068uF
capacitor in position C3, change R3 to 51K, and change R4 to 510K. These
values should be considered a good starting point. You may want to experiment
with the values of C3 and R4 to get better sounding audio. We have had
consistently good results with this de-emphasis network.
The receiver must provide a signal present indication (also called COR, RUS,
CAS) to the controller. Because of the varieties of polarity and state that this
signal can take, we have chosen to implement the controller's signal present input
with an opto-isolator (ISO1). The anode and cathode of the LED in the opto-
isolator are exposed through a current limiting resistor (R30). This allows easy
interfacing to active-high, active-low, and combinations of both to indicate the
presence of a received signal to the controller. Clever wiring can allow the user to
create CTCSS and COR, CTCSS or COR, etc. configurations. Note that both the

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Copyright © 2000, NHRC LLC
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CAS+ and CAS- terminals must be connected to something in order for the
controller to detect the signal present indication.
Transmitter audio can be fed directly into the microphone input of the transmitter.
VR2 (marked TX LVL) is the master level control, used to set the audio level into
the transmitter. The transmitter's deviation limiter (sometimes called IDC) should
be set such that the transmitter cannot overdeviate, regardless of input signal
level. One way to adjust transmitter deviation is to set the transmitter deviation
limiter wide open (unlimited), adjust the controller's master output until the
transmitter is slightly overdeviating, then set the transmitter's deviation limiter to
limit just below 5 KHz deviation. Then reduce the controller's master output until
the transmitted audio does not sound compressed or clipped. Transmitter
deviation should be adjusted with a service monitor or deviation meter.
Transmitter keying is provided by a power MOSFET (Q6) configured in an open-
drain circuit. This can be used to key many transmitters directly. The MOSFET
essentially provides a closure to ground for PTT. For other transmitters, the
MOSFET can drive a small relay to key the radio. Although this MOSFET can
handle several amps, we recommend that no more than 250mA of current be
drawn through it, because the trace on the PC board is somewhat narrow.
2. Adjusting the Audio Levels
Preset all potentiometers to midrange. Connect an oscilloscope probe or DVM to
pin 15 of U3 (the M8870 DTMF decoder). (Use the power supply ground for the
'scope's ground or the DVM's return.) Key a radio on the input frequency, send
some touch-tones, and adjust VR1 (marked RX LVL) until DTMF decoding is
reliably indicated by a 5-volt level on U3 pin 15. Disconnect the oscilloscope or
DVM. Adjust VR2 (marked TX LVL) to adjust transmitter deviation, ideally
measured with a deviation meter or service monitor. Adjust VR6 (the beep level)
to set the courtesy tone and CW tone level.
The easiest way to adjust the ISD1420 input and output level is to select the
simplex repeater mode and record messages until the audio sounds right. VR3
(marked RECORD LVL) adjusts the record audio level into the ISD1420. Adjust
this control for the best sounding record audio. VR5 (marked SPEECH LVL) sets
the ISD1420 playback level. Adjust this control for best acceptable transmitter
deviation. VR4 (marked PROC RX LVL) is used to set the receiver audio level,
and may not need to be adjusted from midpoint.
3. Initializing the Controller
To initially program your secret code into the controller, you must apply power to
the controller with the pins on the INIT jumper, (SW1) shorted, putting the
controller into the initialize mode. Remove the jumper a few seconds after power
is applied. All of the values stored in the EEPROM will be reset to defaults, and

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Copyright © 2000, NHRC LLC
All Rights Reserved.
the controller will be ready to accept the 4-digit secret access code. This will
reset the CW ID to the default value "DE NHRC/2" as well. When the controller
is in the initialize mode the courtesy tone is 1/2 second long, instead of the usual
1/5 second. Key up and enter your 4-digit access code. The controller should
respond with the normal (1/5 second) courtesy beep. The secret access code is
stored in non-volatile memory in the PIC16F84 microcontroller. You will use
this code as the prefix for all commands you send to the controller.
2. Programming
1. Controller Modes
The controller can operate in 3 different modes:
• Repeater Controller Mode
The controller operates a full-duplex repeater, with a courtesy tone and
stored voice messages.
• Link Controller Mode
This is a variation of Repeater Controller Mode where the ISD1420 voice
storage chip can be deleted to lower the cost of the controller. This mode
is intended to control remote receivers that are essentially crossband
repeaters. Normally, when using link controller mode, the hang time is set
to 0 seconds, and the controller is programmed to suppress DTMF muting,
so the user's DTMF commands will appear on the input of a "downstream"
controller. The controller adds remote control, a timeout timer and CW ID
capability to remote or link receivers.
• Simplex Repeater Controller Mode
This mode allows simplex (as opposed to duplex) radios to be used as
repeaters. Up to 20 seconds of received audio is stored in the ISD1420
voice storage chip, and is "parroted" back when the user unkeys. The ID
message is played in CW.
2. Programming the Controller
All programming is done by entering 8-digit DTMF sequences. The first 4 digits
are the passcode chosen at initialization. The next 2 digits are an address or a
function code. The last 2 digits are the data for address or function. To enter
programming information, you must key your radio, enter the 8 digits, then
unkey. If the controller understands your sequence, it will respond with "OK" in
CW. If there is an error in your sequence, but the passcode is good, the controller
will respond with "NG". If the controller does not understand your command at
all, it will not respond with anything other than a courtesy beep, and then only if
the courtesy beep is enabled.

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Responses to Commands
Response Meaning
"OK" Command Accepted
"NG" Command address or data is bad
courtesy beep
or nothing Command/password not accepted
If you enter an incorrect sequence, you can unkey before all 8 digits are entered,
and the sequence will be ignored. If you enter an incorrect address or incorrect
data, just re-program the location affected with the correct data.
In order to save space, reduce keystrokes, and eliminate some software
complexity, all programming addresses and data are entered as hexadecimal
numbers. Hexadecimal (or hex, for short) is a base-16 notation that is particularly
convenient for use in digital computer systems because each hex digit represents 4
bits of a value. The controller uses pairs of hex digits to represent 8-bit values for
the address and data of programming information. Any decimal number from 0 to
255mayberepresentedbytwohexdigits. Hexdigitsare0,1,2,3,4,5,6,7,8,
9, A, B, C, D, E, F, where A through F represent values from 10 to 15. To
convert a decimal number from 0 to 255 to hex, divide the decimal number by 16.
The quotient (number of whole 16s) forms the left (high) digit, and the remainder
forms the right (low) digit. Thus, 60 decimal = 3 x 16 + 12 = 3C hex.
The DTMF keys 0-9 and A-D map directly to their corresponding digits.
Use the *key for digit Eand the #key for digit F.
A 16-key DTMF generator is required to program the controller.
1. Programming the Timers
Timer Resolution. The timer values are stored as an 8-bit value, which
allows a range of 0 to 255. Some of the timers require high-resolution
timing of short durations, and others require lower resolution timing of
longer durations. Therefore, timers values are scaled by either 1/10, 1, or
10 seconds, depending on the application.

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Timer Address and Resolution
Timer Address Resolution
Seconds Max. Value Seconds
Hang Timer 02 1/10 25.5
Timeout Timer 03 1 255
ID Timer 04 10 2550
Enter the 4 digit passcode, the timer address, and the timer value, scaled
appropriately. For example, to program the Hang Timer for 10 seconds,
enter pppp0264,wherepppp is your secret passcode, 02 is the hang timer
address, and 64 is the hexadecimal value for 100, which would be 10.0
seconds.
2. Programming the CW Messages
CW messages are programmed by storing encoded CW characters into
specific addresses in the controller. Use the Morse Code Character
Encoding table and the Programming Memory Map to determine the data
and address for the CW message characters. For example, to program
"DE N1KDO/R" for the CW ID, you would use the following commands:
CW ID Programming Example
DTMF
Command Address Data Description/Purpose
pppp0#09 0F 09 D
pppp1002 10 02 E
pppp1100 11 00 space
pppp1205 12 05 N
pppp133* 13 3E 1
pppp140D 14 0D K
pppp1509 15 09 D
pppp160# 16 0F O

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pppp1729 17 29 /
pppp180A 18 0A R
pppp19## 19 FF End of message marker
The CW ID can store a message of up to 40 characters. Do not exceed 40
characters.
3. Programming the Flag Bits
Controller features can be enabled of disabled with the use of the
Configuration Flag Bits. These bits are encoded into a single byte, which
is programmed into the controller at address 01. Multiple flag bits can be
selected by summing their hex weights. For instance, to set up a link
controller with no ISD1420, no courtesy tone, and suppress the DTMF
muting, you would add 01, 10, and 20 to produce hex 31, which you
would then program into address 01 in the controller as pppp0131.
Configuration Flag Bits
Bit Hex
Weight Feature
001 ISDAbsent
1 02 Simplex repeater mode
204 n/a
308 n/a
4 10 suppress courtesy tone
5 20 suppress DTMF muting
6 40 use tail message for courtesy tone
780 n/a
4. Recording the Voice Messages
Stored voice messages can be played and recorded, and CW messages can
be played by using the message commands. Command 40 is used to play

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stored voice or CW messages, and command 41 is used to record stored
voice messages.
To record stored voice messages, use command pppp410x,wherexis the
number of the message you want to record, found in the message contents
table. Unkey after the command sequence, then key up, speak your
message, and unkey. The controller will remove about 100 ms from the
end of your message to remove any squelch crash that might have been
recorded.
To play stored voice messages, use command pppp401x,wherexis the
number of the stored voice message you want to play. To play CW
messages, use command pppp401x,wherexis the number of the CW
messageyouwanttoplay.
You may wish to have a family member or member of the opposite sex
record your ID messages. The recorded audio sounds natural enough that
people have actually tried to call the amateur whose callsign is recorded in
the controller after the ID message plays!
3. Enabling/Disabling the Repeater
The repeater can be disabled or enabled by remote control by setting the value in
location00. Setthislocationtozerotodisable,ornon-zerotoenable. For
instance, to disable the repeater, send command pppp0000. To enable the
repeater, send command pppp0001.
3. Operating
1. About the IDs
When the repeater is first keyed the controller will play the "initial ID". If the
repeater is keyed again before the ID timer expires, the controller will play the
"normal ID" when the ID timer expires. If the repeater is not keyed again, and the
ID timer expires, the controller will reset and play the "initial ID" the next time
the repeater is keyed. If the repeater is keyed while the controller is playing a
stored voice message ID, the controller will cancel the stored voice message ID
and play the CW ID.
The idea behind this IDing logic is to prevent unnecessary IDing. For instance, if
a repeater user keys the machine and announces "This is N1KDO, monitoring",
the controller will play the initial ID, and no further IDing will occur unless the
repeater is keyed again. If users commence with a QSO, keying the repeater at
least once more, the controller will play the normal ID and reset the ID timer
when the ID timer expires. If the repeater becomes idle for one ID timer period
after the last ID, then the next time it is keyed it will play the initial ID. The

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intent is that the repeater users only hear the initial ID the first time that they key
the repeater.
2. The Tail Message
The controller supports a "Tail Message" that plays the nth time the hang timer
expires. The number of times the hang timer must expire before the tail message
plays (n) is the "tail message counter" at address 5. The tail message counter can
be set from 1 to 255. The tail message is disabled if the tail message counter is
set to 0. Program the tail message counter value into address 05.
3. Using the Tail Message as the Courtesy Tone
The tail message can be used as the courtesy tone if bit 6 is set in the
configuration flags. In this case, you will likely want to set the tail message
counter value to 0 to keep the message from playing twice occasionally. The
message could store the sound of a bell, a dog's bark, or the repeater trustee
saying "what?"!
Tables
Message Commands
Command Description
400x 0 <= x <= 3, play CW message x
401x 0 <= x <= 3, play voice message x
410x 0 <= x <= 3, record voice message x
Message Contents
Message
Number Stored Voice CW
0 Initial ID ID message
1 Normal ID message timeout message ("TO")
2 Time-out Message confirm message ("OK")
3 Tail Message invalid message ("NG")

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Programming Memory Map
Address Default
Data Comment
00 01 enable flag
01 00 configuration flags
02 32 hang timer preset, in tenths
03 1e time-out timer preset, in seconds
04 36 id timer preset, in 10 seconds
05 00 tail message counter
06 0f 'O' OK Message
07 0d 'K'
08 ff EOM
09 05 'N' NG Message
0a 0b 'G'
0b ff EOM
0c 03 'T' TO Message
0d 0f 'O'
0e ff EOM
0f 09 'D' CW ID starts here
10 02 'E'
11 00 space
12 05 'N'
13 3e '1'
14 0d 'K'

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15 09 'D'
16 0f 'O'
17 29 '/'
18 0a 'R'
19 ff EOM
1a 00 can fit 6 letter ID....
1b-37 not used
38 n/a isd message 0 length, in tenths
39 n/a isd message 1 length, in tenths
3a n/a isd message 2 length, in tenths
3b n/a isd message 3 length, in tenths
3c n/a passcode digit 1
3d n/a passcode digit 2
3e n/a passcode digit 3
3f n/a passcode digit 4

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Morse Code Character Encoding
Character Morse
Code Binary Encoding Hex Encoding
sk ...-.- 01101000 68
ar .-.-. 00101010 2a
bt -...- 00110001 31
/-..-. 00101001 29
0----- 00111111 3f
1.---- 00111110 3e
2..--- 00111100 3c
3...-- 00111000 38
4....- 00110000 30
5..... 00100000 20
6-.... 00100001 21
7--... 00100011 23
8---.. 00100111 27
9----. 00101111 2f
a.- 00000110 06
b-... 00010001 11
c-.-. 00010101 15
d-.. 00001001 09
e. 00000010 02
f..-. 00010100 14
g--. 00001011 0b

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h.... 00010000 10
i.. 00000100 04
j.--- 00011110 1e
k-.- 00001101 0d
l.-.. 00010010 12
m-- 00000111 07
n-. 00000101 05
o--- 00001111 0f
p.--. 00010110 16
q--.- 00011011 1b
r.-. 00001010 0a
s... 00001000 08
t- 00000011 03
u..- 00001100 0c
v...- 00011000 18
w.-- 00001110 0e
x-..- 00011001 19
y-.-- 00011101 1d
z--.. 00010011 13
space 00000000 00
EOM 11111111 ff

NHRC-2 User Guide
NHRC-2 Assembly Guide Page 1 3/16/2000
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NHRC-2 Repeater Controller
Assembly Guide
Rev D PCB only
The NHRC-2 Repeater Controller is a fairly simple project to build. Minimal electronic
experience is required. Assembly time should be around 1 hour.
1. Organize your parts as per the Bill of Materials. All resistors in this kit are mounted
vertically on the PCB. You may want to form the resistor leads ahead of time. Simply
bend the resistor lead over. (Hint: Try to keep the color code bands consistent top to
bottom throughout the board, oriented such that the tolerance bands of the resistors all
face in the same direction). Note that pin 1 of many components is denoted by the square
pad on the PCB. You will be working from your parts list and matching components
from the parts list to their appropriate location on the PCB. As you install a part check it
off on your parts list. You can also use the “Board Layout” image located on page 2 of
your User Guide as a reference for parts placement.
2. Insert the capacitors into the PCB. Be careful to install the polarized caps correctly. The
square pad always goes to the positive (+) lead of the capacitor. Capacitors such as the
0.1uF bypass caps are non-polarized and do not have a square pad. They may be inserted
either way. (Note: Double check your work, tantalum capacitors may explode upon
power up if they are inserted backwards. Be careful not to mix up C20 (33pF) with any
of your bypass caps, they look similar.)
3. Insert the resistors. The PCB silkscreen has a circle around the pad that the resistor body
will sit above and a line from the circle indicates where the other lead goes. Be careful to
match the reference designator to the proper component location. If in doubt find the
component in the schematic and use an ohmmeter to identify the component location in
question. Some reference designators may be crowded among other reference
designators and may have a line drawn to the proper component location. (Note: Pay
special attention to the placement of resistors R4 and R11. Resistor R4 is located next to
C3 and R11 is located next to C8.)
4. Install the voltage regulator, U4 (LM7805) and power MOSFET Q6 (IRF510). All of
these components are installed with the heat sink surface facing out from the board.
(Note: These parts should not require mounting to a heat sink.)
5. Install the other transistors and FET's. Q2, Q3, and Q4 are PN2222, Q1 is an MPF102
JFET, and Q5, which is a 2N3906.
6. Install the zener diode, D1 (1N5226) so that the cathode (the end with the band) goes into
the square pad. (Note: Zener diode D2 (1N5240) does not need to be installed.)

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7. Install the crystal, Y1, being careful not to have the part body contact the trace below it.
Lifting Y1 up slightly off the PCB or using a dab of RTV or “hot glue” under the part
before soldering will solve this.
8. Install pots, VR1, VR3, VR4, VR5 & VR6 which are 10K (marked "103") and VR2
which is 500K (marked "504").
9. Install connector P1, and 2 pin header SW1.
10. Install the chip sockets. (Note: Install them so that designator for pin 1 is per the notch
shown on this chip socket on the silkscreen.) Do not install your chips at this time.
You will need to do some power up checks first.
11. Solder all of your connections using a small soldering iron of approx. 25-40 watts. (DO
NOT USE A SOLDERING GUN). Use a "63/37" rosin flux-core solder and use care not
to overheat the PCB. Carefully trim the leads of the bottom of the PCB. Clean the PCB
to remove flux residue with alcohol. You may also consider using a water-soluble flux-
core solder (such as Alpha Metals Aqualine 6000). A quick rinse under warm water in
your sink after assembly and your finished product will look professional.
12. Double-check your work. Check for any unsoldered parts, solder bridges, or improper
part placement.
You are now ready to apply power to the PCB and check some voltages before installing the IC
chips. See the Users Guide for assistance with assembly of the connections required. Apply
power and check that the +5V regulator is working and that +5 volts (VCC) is being supplied
where needed (Example: U1 pin 14, U2 pins 16 & 28, etc.). Check that VREF is approximately
1/2 of your input supply voltage is at U5 pins 3 & 5. When you are confident that all of your
voltages are OK then you are ready to install your chips. After which you can power the PCB
back up, INIT the processor (following the procedure in the Users Guide) and enjoy!
If you encounter problems go back and recheck your work, look for unsoldered connections,
solder bridges or misplaced components.
Look at the Assembly FAQ and the Troubleshooting Guide included in the Users Guide or visit
the NHRC-2 web site http://www.nhrc.net/nhrc2 for more detailed trouble shooting
instructions. We also offer troubleshooting support by email [e-mail]. The circuit
is fairly simple and most problems can be resolved quickly.
Alpha Metals solder info is available at http://www.alphametals.com

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NHRC-2 Repeater Controller
Frequently Asked Questions about Assembling a Partial Kit
Rev D PCB only
I have some ISD1020s lying around. Can I use them in the NHRC-2?
Not easily. The ISD1000 series parts use a slightly different interface for
record/play, power down, and chip select. To use an ISD1000 series part would
require some changes to the PC board, and some software changes as well. These
changes are not impossible, in fact the original prototype controller used an
ISD1020, but the ISD1420 is a less expensive, newer part.
What if Digi-Key is out of stock of the DB9 connector?
If the NorComp part listed in the BOM is unavailable, Digi-Key does not offer a
good sub. Two acceptable subs are: Newark Electronics P/N: 87F2251 (Amphenol
617-C009S-AJ120 $0.98ea.) or RadioShack P/N: 910-1546 ($1.90ea.) These
devices have the proper offset (0.318") and board mount locks, however neither
part comes with jackscrews. These are available separately using Newark P/N:
50F4689 (Keystone 7228 $0.24ea.) Some kit builders have reported that the AMP
Amplimite 754781-4 (Digikey A2100-ND), will fit in the board, but extreme care
must be taken if this part is used to make sure that none of the traces on the PC
board under the connector are shorted out. Use some electrical tape or Mylar sheet
to insulate the connector housing from the board.
I built my controller, and it doesn't work. What can I do?
Look at the Troubleshoot Guide contained in your documentation or the
Troubleshooting Information page at http://www.nhrc.net/nhrc2/troubles.html for
some ideas to get your controller running.
I want to build a controller without the ISD1420, because I don’t desire speech or for use
as a link controller. What parts are not needed?
You can leave the following parts off the board:
C5, C9, C12, C15, C18, C23, C24, C25
Q3, Q4
R9, R10, R13, R20, R21, R24, R25, R26, R27, R28
U2
VR3, VR5
Remember to set bit 0 of the configuration flag to indicate to the microprocessor
that the ISD1420 is not present. Consider setting bits 4 and 5 as well, depending on

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your linking requirements.
What's all this about de-emphasis, and why should I care?
De-emphasis is used to remove the pre-emphasis put on a FM signal by the
transmitter. Together, they work to reduce the amount of hiss you hear in a received
FM signal. The concept is similar to Dolby noise reduction: the transmitted signal
has the high-frequency component boosted before transmission, and then a
corresponding reduction occurs in the receiver. The receiver removing a significant
part of the high-frequency component of the received signal actually removes a lot
of hiss and noise with it.
If you use receiver audio that has not been de-emphasized (like what is commonly
found on the high side of the squelch control), then the repeated audio will sound
very tinny and unnatural. However, the high side of the squelch control is a good
place to take audio from a receiver used in a repeater because the audio there is not
subject to level changes caused by the volume control. In many radios, the de-
emphasis filter is "downstream" of the volume control, which makes taking audio
from there unattractive.
The NHRC-2 has the capability to perform de-emphasis filtering on board. To use
the onboard filter, some parts substitutions must be performed. It is probably easier
to decide whether you want the filter or not before soldering part to the board.
Component No De-emphasis With De-emphasis
C3 Not present .0068uF
R3 100K 51K
R4 100K 510K
I seem to be “falseing” the DTMF decoder frequently. What’s the problem?
First try adjusting the level of VR1 (RX LVL) down. If the signal level is too high
it could be overloading the decoder. You can also try replacing R22 (300K) with a
470K ohm resistor. This speeds up the time constant of the DTMF decoder slightly,
and should help eliminate “falseing”.
There seems to be some distortion in the repeated audio. What can I do?
Try replacing U5 (the LM358) with a TL062CP (available from Digi-Key P/N:
296-1771-5-ND), or install a 4.7K resistor from U5 pin 7 to ground. Do not use
both modifications.

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Copyright © 2000, NHRC LLC
All Rights Reserved.
NHRC-2 Repeater Controller
Troubleshooting Guide
Rev D PCB Only
Power-related problems
Check all of your solder joints carefully. A poorly soldered or an
unsoldered joint can cause all sorts of problems. Solder joints should
appear bright and shiny, and the solder should taper from the end of the
pin to the pad on the board; there should not be a "blob" of solder on the
pin. Make sure that there are no solder "bridges" between pads or traces.
It is very easy to create solder bridges between the IC pins; these pins are
only 1/10 inch apart.
Apply power with all the chips removed from their sockets and an
ammeter in series with the +12 volts (pin 2 of P1 on the controller). There
should be an extremely small amount of current flowing into the board
with the IC's removed, typically less than 5mA. If there is more current,
check component placement, and ensure that there are no solder bridges
on the board. Remove the ammeter, and re-apply power. With all of the
chips still removed, check for +5 volts at pin 3 of U4 (LM7805), pin 14 of
U1 (PIC16F84), pin 28 of U2 (ISD1420), and pin 18 of U3 (M8870). If
any of the power supply voltages are not right do not insert the chips
until this problem is found and corrected.
Make sure the PIC16F84 is in the correct socket on the board. The M8870
sits in the socket nearest to the crystal. Make sure the chips are plugged in
correctly, with pin 1 corresponding with the square pad on the PCB.
Improper installation of the chips can destroy them! If you had any of the
chips in backward they may be “nuked”.
CAS Signal problems
The easiest way to verify correct operation of the CAS signal is to remove
ISO1 (4N36) from its socket, and plug a LED in instead. The LED's
anode (the "+" leg, usually longer) goes into pin 1, and the cathode
(the "-" leg, usually shorter) goes to pin 2 of the socket. If you are unsure
of which leg of the LED is which, test it with +12 volts and a 1Kohm
resistor in series with the LED. When the CAS signal is correctly applied,
the LED should glow. A dim glow is probably OK. If the LED lights up
very brightly, or “smokes”, it is likely that the CAS signal's voltage is too

NHRC-2 User Guide
NHRC-2 Troubleshooting Guide Page 2 3/16/2000
Copyright © 2000, NHRC LLC
All Rights Reserved.
high. In this case, ISO1 has probably been destroyed. Replace R30
(1.5Kohms) with a higher value, calculated to allow approximately 10mA
to flow through the LED in the opto-isolator. We do not recommend CAS
signal voltages of more than 30 volts.
If the LED will not glow, make sure that there is at least +3 volts on pin 6
of the DB9 connector (P1), measured against pin 7, when the CAS signal
is present. The LED must glow when the CAS signal is present.
If the LED glows when CAS is applied, but the controller never seems to
"see" that the signal is there, you can test the entire CAS path in the
controller by using a DVM to measure the voltage on pin 13 of U1
(PIC16F84). Pin 13 should be near +5 volts when the CAS signal is not
present, and should fall to near 0 volts when the signal is present.
PTT Signal problems
If the power is not good, or the CAS signal is not good, you will never get
PTT (push-to-talk). These sections should be verified before worrying
about the PTT circuit.
Pin 7 of U1 (PIC16F84) should normally be around 0 volts, and should
rise to about +5 volts when the controller turns PTT on. If not, verify the
CAS signal is working, then examine the section in this document on a
completely dead controller. When PTT is turned on, the gate (pin 1) of
Q6 should rise to about +5 volts. If not, then either Q6 is bad (shorted) or
R29 is open or incorrectly installed.
The controller supplies PTT as a closure to ground. If the controller is
interfaced to the repeater correctly, there should be some positive voltage
on the drain (pin 2) of Q6. When the controller turns PTT on, this positive
voltage should drop to near 0 volts. If there is no positive voltage on pin 2
of Q6, then check the interface to the transmitter's PTT line.
Completely Dead Controller
If the controller appears completely dead, and none of the power, CAS, or
PTT symptoms are found, then the problem may be related to the
microprocessor. Measure the DC voltage on Pin 4 of U1 (PIC16F84) with
a DVM. This pin should have around +5 volts on it. If it does not, check
R17, R18, R19, Q5, and D1. Make sure that D1 is installed correctly, with
the banded end of the diode mounted into the square pad on the PCB.
Make sure that Q5 is oriented correctly, and verify the values of R17, R18,
and R19.
If U1 pin 4 has about +5 volts on it, make sure that the 3.58 MHz clock is
running. Use an oscilloscope to look at U1 pin 15. This pin should have a