MIC-E.txt            INTEGRATING APRS ON VOICE CHANNELS         
Ver Mic104e                 and VOICE REPEATERS                
                       Copyright 1993,4,5,6 WB4APR

NEW:  See notes below on new Mic-E telemetry format in MIC104d and APRS77f.

    As mobile GPS/APRS continues to grow, we can eliminate the need for 
every mobile to have a TNC, digital radio, and second antenna by simply 
integrating the position report into a very brief tone burst at the 
end of a voice tramnsmission over any two-way radio.  With this scheme, 
no additional hardware is required in the vehicle, other than a GPS unit.  
The system not only reports position and vehicle type, but also one of 
7 messages, a BeaconText, and 3 analog telemetry values!

     By transmitting a position report at the end of a voice transmission,
not only is this a period of dead time due to the almost universal 
courtesy beeps found on amateur repeaters, but the tone burst can be 
easily muted out at the repeater receiver, so that the other mobile users 
do not hear it!  If the tone burst is about 0.3 seconds, then it will be 
virtually transparent to voice repeater operation.  The APRS MIC-ENCODER
achieves a complete position report, course, speed, and digipeater 
information in about 30 bytes including header, instead of the 90 or more 
bytes in a normal APRS position report.

     At the voice repeater receiver, a TNC picks off the position report 
and digipeats it out onto the dedicated APRS digital frequency for mobile 
position reporting.  Although any TNC can be used, a special TNC is being 
developed that determines the path based only on the bits in the TO-SSID 
instead of the usual long string of digipeaters.  This makes the packet 
very short.  In addition, the special APRS NODE TNC appends the repeater 
frequency onto the end of the position report so that digital users can see 
where the packet originated.  If all voice repeaters digipeated onto the 
same digital position reporting channel (usually 145.79 if available) then 
anyone monitoring the APRS frequency will see ALL mobile position reports 
from ALL GPS mobiles on ALL frequencies!


APRS MIC ENCODER:  In order to make the APRS LOCATOR SYSTEM practical, 
the MIC-ENCODER had to meet several design constraints:

   * Must interface to UNMODIFIED radios via the MIC connector
   * Must use standard AX.25 for compatibility with existing TNC's
   * Must compress position report into about 0.3 seconds
   * Must be low enough in power to be powered from the MIC jack
   * Must accept the standard NMEA output from GPS receivers
   * Optionally has 3 analog channels for telemetry, and an identifying
     beacon text

The result is a 1200 baud position report compressed to 32 bytes including
beginning and ending FLAGS.  This equates to about 320 ms, including
CALLSIGN, DIGIPEATER PATHS, and a minimum message capability.  Plus, the 
packets are still receivable on ANY AX.25 TNC.


PACKAGING:  Although the electronics could be miniaturized into about 
1 cubic inch, the requirement for user access to switches and the 
requirement for withstanding the pulling and tugging on the MIC cord
results in a robust dash board box design.  The cicruit may be powered by 
the mic connector and the only external input is via a standard 1/8 inch
phone jack or DE-9 connector to receive the NMEA data from the GPS unit.  
This makes the entire mobile vehicle position reporting system as portable 
as the microphone!  Simply move the MIC from vehicle to vehicle, and as 
long as the radios are compatible at the MIC connector, then the vehicles 
are GPS ready!  The front panel for the MIC ENCODER is shown below.
It connects to the radio with only a single 7 conductor pigtail back to 
either a back-to-back JACK/PLUG or soldered in parallel to the existing 
MIC jack.
                          
  -----------------------------------------------------------------------
  |  PERIOD    R C V   OMNI    DIR      SSID     DIGI    AUTO   POWER   |
  |            L V L     7  N  S           7  0  1               O N    |
  |    /^\             6         E |     6         2                    |
  |   /   \     (O)   5   / - \   W     5   / - \   3     O       O     |
  |  | (O) |         4   |     |   N+  4   |     |   4   (O)     (O)    |
  |   \___/     (O)   3   \ - /   S+    3   \ - /   5                   |
  |  min               2         E+      2         6                    |
  |            P T T     1  0  W+          1  0  7                      |
  |            O U T    P  A T  H       M E S S A G E   O F F   O F F   |
  -----------------------------------------------------------------------
                    
     On the APRS MIC ENCODER, the configuration switches give the operator 
real-time control over other dynamic MIC choices as follows:

     ON/OFF - Used to enable or disable the Mic Encoder packets
     AUTO   - Enables auto-packets if repeater has been quiet for N secs.
     PATH   - Used to set digi HOPS or North/South/East or West routes
     MSG    - Selects 1 of 7 messages AND selects DIGI or SSID mode
     PERIOD - Used to change the reporting period

     Normally the MIC encoder will only send a POSIT if the POSIT timer has  
elapsed AND the user has been talking AND releases his PTT.  In the AUTO 
mode, however, after a specified AUTO time period, AND after the repeater 
has been silent for the QUIET period, then a position packet will be 
initiated and transmitted.  Most voice repeaters will never even key up on 
such a brief burst due to their built in ker-chunk filters.  The TNC on the
repeater input, however, will hear it and digipeat it normally.  Note, for 
the QUIET timer to work properly, the receiver's audio must be set high 
enough to occassionally flicker the RCV LED.

           
MESSAGE BITS:  The 3 message bits select one of seven pre-defined messages 
as follows.  In addition, all message numbers above 3 will change your 
symbol color as shown.

   MSG    COLOR    DEFAULT DEFINITION
   ---   -------   -------------------
    0    normal    Off duty
    1    normal    Enroute 
    2    normal    In Service
    3    normal    Returning
    4    dim yel   Committed
    5    Brt yel   Special
    6    dim red   PRIORITY     Trips alarms & centers all maps to unit
    7    Brt red   EMERGENCY!   Trips alarms & centers all maps to unit


ROUTING PATH:  

    There are actually two routing systems, one that can use standard TNC's 
at the repeater and the other that takes advantage of a new specialized 
APRS NODE TNC.  We will call the standard mode the DIGI mode and the other, 
the SSID mode.  In the DIGI mode, the path switches just select how many 
hops along one of two preset digi strings will be transmitted in the packet.   
The advantage of this method is that it is compatible with ANY TNC and will 
work with existing systems.   The disadvantage is that each digi hop takes 
7 bytes, and just a 3 hop path almost doubles the length of the packet.  
The second mode uses only the 4 SSID bits for all routing information.  
This keeps the packet short, while also allowing for up to 7 hops in all 
directions!  The high order PATH bit selects between OMNI or DIRECTIONAL 
routing and the 3 routing bits are used to tell the repeater how to route 
the packet.  

     The following table shows how the routing is handled in both the 
DIGI and SSID mode.  In DIGI mode the TO-SSID is always 0 and the actual 
digi path is included in the packet.  In SSID mode, there are no digis 
transmitted and the switch setting are transmitted in the 4 bits of the 
TO SSID.  In the following example, assume the MIC-ENCODER has been loaded 
with the digi string of RELAY,WIDE,WIDE,DIG4,DIG5,DIG6,DIG7
   
D/O PATH SSID DIGI MODE            SSID MODE AS DIGIPEATED BY THE NODE
--- ---- ---- -------------------  ----------------------------------
 0  000  0    none                 none 
 0  001  1    RELAY                WIDE-1
 0  010  2    RELAY,WIDE           WIDE-2
 0  011  3    RELAY,WIDE,WIDE      WIDE-3
 0  100  4    DIG4                 WIDE-4
 0  101  5    DIG4,DIG5            WIDE-5
 0  110  6    DIG4,DIG5,DIG6       WIDE-6
 0  111  7    DIG4,DIG5,DIG6,DIG7  WIDE-7
 1  000  8    none                 NORTH UNPROTO path
 1  001  9    RELAY                SOUTH UNPROTO path
 1  010  10   RELAY,WIDE           EAST  UNPROTO path
 1  011  11   RELAY,WIDE,WIDE      WEST  UNPROTO path
 1  100  12   DIG4                 NORTH UNPROTO path + WIDE
 1  101  13   DIG4,DIG5            SOUTH UNPROTO path + WIDE
 1  110  14   DIG4,DIG5,DIG6       EAST  UNPROTO path + WIDE
 1  111  15   DIG4,DIG5,DIG6,DIG7  WEST  UNPROTO path + WIDE

 In this example, the Mic-Encoder was programmed with a via path of
 RELAY,WIDE,WIDE,DIG4,DIG5,DIG6,DIG7.

CONVENTIONAL DIGIPEAT ROUTING:  First notice that in the DIGI mode, the 
paths 0 through 3 simply select the number of digi hops in the original 
string to use.  The paths 4 to 7 start over again at the 4th position.  
This can be thought  of as a completely independent second DIGI string.  
Typically you would set the path to RELAY,WIDE,WIDE,WIDE,WIDE,WIDE
If you select 4 you get WIDE, if you select 5 you get WIDE,WIDE 
and so on.  THis separation into two distinct strings gives you the chance 
to have a path beginning with RELAY or beginning with WIDE.  This is
important for operating in areas which do not yet have the dual alias
WIDE-RELAY digipeaters yet.  Although the longest path is now limited
to four hops, anything beyond 2 WIDES is frowned on anyway...

REPEATER TNC ROUTING:  If the TNC is just a conventional TNC, then it
digipeats simply according to the path included in the Mic-E packet.
The special APRS NODE, however, has two routing methods, depending 
on whether the surrounding APRS packet network is capable of the WIDE-N
algorithm or not.  If WIDE-N is available, then the APRS REPEATER node
simply digipeats the packet to WIDE-N where N is the number of hops
indicated in the packet SSID.  If N is greater than 7 then it is a
directional packet and the North, South, East, or West paths stored
at the NODE are used.  If WIDE-N is not yet available, then the NODE
builds a digipeater string using the same algorithm as the MicEncoder;
offering the optional 3 and 4 hop alternatives for 1 through 7 and
still uses the directional paths for numbers greater than 7.  ALso
in the directional path, if the 3rd SSID bit is set, then a WIDE is 
added to the end of that path.
 
WIDE-N ROUTING:  In WIDE-N mode, every APRS digipeater repeats every WIDE-N 
packet it hears and then subtracts ONE from the SSID.  They also keep 
copies of all such packets (or just keep a checksum) for 60 seconds and 
ignore all DUPES of the same packets.  THis is a very effecitve OMNI 
routing method that permits the packet to go out N hops in all directions 
without any duplication!

IMPLEMENTATION:  The key to the success of the MIC-ENCODER is that it
is very versatile and can operate in all required modes.  This allows  
for growth and improvment in the APRS systems without obsolesence.
There are five possible operational situations as follows:

NO TNC  AT  REPEATER:    MIC-E path is set to 0 and anyone monitoring the
(OR SIMPLEX VOICE)       the repeater output with APRS can track users.

NO TNC  AT  REPEATER:    MIC-E path is set to 2 (RELAY,WIDE) and someone's
(But TNC @ someones QTH) home station monitors the REPEATER output with
                         his TNC and DIGI's the packet over onto APRS

STANDARD TNC @ REPEATER: MIC-E path is set to 1 thru 7 in DIGI mode.  
                         The TNC with the alias of RELAY (or WIDE) 
                         repeats packets onto the APRS packet channel.

APRS NODE @ REPEATER:    NODE routes according to MIC-E SSID bits only.

DIGITAL  APRS CHANNEL:   MIC-E path can be 1 thru 7 in DIGI mode.

The BIG difference between the MIC-E DIGI mode and the SSID mode is the 
length of the packet due to the DIGI fields.  THis means for interim 
compatibility, MIC-E users can operate generally with a path of 1,2, or 
3 on all possible channels without specific configuring.  Of course, if 
they select SSID mode while on an APRS NODE repeater channel, their
packets will be much shorter because they will be routed by the SSID alone.

SETTING DIGI or NODE MODE:  To save front panel space, the high order bit 
of the MESSAGE switch is used to select between the DIGI mode and the SSID 
mode, the Mic-E then checks this 4th bit to determine how to send each
packet.  THis way a user can change between SSID and DIGI mode to match
the configuration of the particular repeater he is currently using..  
The front panel markings show that with the switch in the right side
places you in DIGI mode, and the left side in SSID mode.

MIC-E PACKETS:  The Mic-E always sends a compressed position report in 
every packet.  If there is no position, then the Lat and Long are 0.  If
Telemetry is enabled, 5 bytes of telemetry are added, and if BText is
enabled then the text is appended onto the end of the POSIT.  The telemetry
is captured on the alt-TELEMETRY screen in APRS and the BText will display 
on the LATEST STATUS page.  NOTE: Since the BText may also contain a fixed 
POSIT in some applications, whenever there is a BText, then the compressed 
posit is ignored in that packet.

MIC-E SETUP AND CONFIGURATION:  The MIC-E is based on the APRS Micro-
Interface-Module (MIM) designed by Dr. Carl Wick (N3MIM) and produced by 
Dr. Will Clement N3LXR.  The MIC-E is configured via its serial port using 
a PC program called MIC104.exe.  This program provides a nominal TNC type 
command mode for setting the MIC-ENCODER configuration giving the user the
standard cmd: prompt.  Once the MIC-E is configured, you use the PERM 
command to cause the MIC-E to save the configuration in EEPROM.  The 
following items can be configured:

     MYCall           Sets the MIC callsign       
     MYSymbol         Sets the APRS symbol character
     VIA digi1,, etc  Sets the Unproto digipeater path
     TXDelay          Sets the key up delay for AUTO packets
     TXDPtt           Sets the key up delay for Mic-E PTT packets
     PERiod           Sets the nominal MIC cycle period
     POSIT N          Sets POSIT period as N * cycle period
     TELEMETRY N      Sets TELEMETRY period as N * POS period
     BEACON N         Sets BEACON period as N * POS period
     AUTO N           Sets AUTO period as N * POS period
     QUIET N          Sets the QUIET period as N * cycle period
     BText            Sets the Beacon Text
     PTT (1:0)        Sets sense of the PTT signal.  For the MIC-E,  
                      this is 1 since an external PTT transistor is used.

MIC-E HARDWARE INTERFACE:

As noted, the MIC-E evolved from a standard MIM with a few external
components to integrate it to the user configuration switches and to the
microphone PTT circuit.  The 8 digital BIT inputs on the MIM are used as 
follows:

  D8, D7, D6, D5  Routing BITS.  These are placed in the TO SSID field 
  D4, D3, D2      Three message bits.  Active low.
  D1              PTT INPUT.  Active LOW.
  AD1             Sets DIGI mode if value is between 0 and 7 out of 255
  AD3             PERIOD Pot multiples the PERIOD by N between 1 and 15.
  HO              The Hold OFF is active LOW
  PTT             PTT output is ACTIVE HIGH since an external PTT 
                  transistor is required.

NOTE:  SInce all bits have internal pull up resistors, then the default
values are "1" so we use ACTIVE LOW negative logic.  A SWITCH to GROUND 
is considered to indicate the condition.  AD1 needs a pullup of 470K if
it is not otherwise interfaced to a non-zero analog circuit.

GPS INPUT STRING:  Currently, ONLY the $GPRMC is supported since
it has both position, course and speed.

   $GPRMC,123456.xx,A,3859.11xx,N,07629.12xx,W,123xxx,321.x,.....

POSIT NOW!  This function was added in Mic-E104e so that you could override
the timers and transmit a packet at any time.  Just turn the PERIOD pot
momentarily to 0 (minimum).  This forces a posit NOW.  You may leave it
at minimum as long as you want (my usual position) since it will only send
ONE packet.  If you are already at 0, just rotate it up a bit and then
back down.  In the Mic-E104e betas there is a jiggle zone about 1/8th of
a turn up where you may end up with CONTINUOUS packets since we forgot
to "de-bounce" the transition across the decision boundary...  Sorry...

USE OF MIC-ENCODER BEACON TEXT:  The Mic-E's BText is included on the
end of a posit report.  But due to APRS processing on receive, only the
BText will get through and the posit will be ignored.  This is why you 
should always set your BText rate at a lower rate than your POSIT rate.
For NON-GPS equipped MIC-Encoders, a null posit 000000/000000 will normally
be transmitted.  For fixed station use, however, you can put your full
LAT/LONG in the BText, and APRS will get the posit from that.  Use the
format of  BT 3859.11N/07629.11W$000/000  Where $ is the usual symbol
character.  If you choose to do this, then you can put no other text
in the BText, or the MESSAGE bits will end up not being properly parsed.

A good example for this, is as a burgler alarm at a fixed location.  Put
the location in the BText as above, and connect the MESSAGE bits and PERIOD 
bit to contact closures in your alarm system.  Have AUTO ON.  When the
bits get tripped, the message rate increases by a factor of 16 and the
message changes to EMERGENCY or PRIORITY...


TELEMETRY: The MIC-E can also send 5 channels of analog telemetry.  Mic104
and prior versions would send 4 channels of telemetry representing the
MIM inputs AD0 through AD3.  In Mic104d the PERIOD pot was moved to AD3 and
AD1 became the SSID/DIGI select bit.  But for compatibility with the MIM 
which could still operate with 5 channels, it was decided to always transmit 
the 5 channels in the MIC format even if AD1 and AD3 were already committed.
This change from 4 to 5 channel format results in the following situations:

Pre-MIC104d > APRS77f:  Telemetry page will show 4 good channels.
                         5th channel will show 0 or first byte of BText
                         1st char of BText will be lost when TLM is xmitted

MIC104d > pre-APRS77f:  TELEMETRY page will show 4 channels.
                        2nd chnl will be 0 or 255 depending on SSID/DIGI
                        3rd chnl will be value of PERIOD pot
                        5th chnl will show --- and become 1st char of BText
                          
DUAL USE ANALOG INPUTS:  Since all 5 channels are now always transmitted, 
the telemetry page will show whether the user is in DIGI mode and what is 
the current setting of his PERIOD pot.  In addition, since the AD1 
only indicates DIGI mode if the analog value is 7 or below, this analog 
input can still be used for analog sensors with outputs between .16 and 5
volts while in SSID mode.  A 470K pull up resistor assures a positive value
when the SSID bit is not grounded.   Additional user momentary push button 
actions are anticipated as dual use applications on the other analog inputs 
as well.

WARNING:  Unless the analog inputs are tied to a voltage through an impedance
of less than 10K they may show some crosstalk to adjacent channels.  If they
are floating, they will surely show random values.  Or in the case of the
dual use, the 470K pull up resistors will show strong positive values near
the maximum 255.


PTT LED INDICATOR:  The PTT LED is connected to the MIC PTT output line that 
shows when the Mic-E is pulling the PTT low.  This shows the user that a 
packet is pending and will be sent when he releases the PTT.

RECEIVER LED:   This LED is connected to a simple audio rectifier of the
receiver audio.  As long as the LED occasionally flickers, the MIC-E will
not AUTO-initiate any packets.  If the LED has not been driven by the
receiver for the period of the QUIET timer, then an AUTO packet is initiated.
If AUTO is set to OFF, then the switch permanently lights the LED and
prevents all AUTO-packets.  Users must set the receiver audio high enough 
to tickle the RCV LED frequently in order for holdoff to work.

WARNING!:  If you turn the audio down because the wife wants quiet, then
your Mic-E will not have a holdoff signal and the AUTO timer may transmit
on the repeater over other users if AUTO is enabled!

RADIO INTERFACING:  THere are three ways to wire the MIC-E to your radio 
system depending on your preference:

    A)  Wire the MIC-E in parallel to your mic at its connector
    B)  Wire the MIC-E internally to the radio or to an auxiliary input
        (But the MIC-E must be able to sense the MIC PTT independently)
    C)  Wire the MIC-E to a back-to-back plug jack combination
    D)  Parallel the MIC-E and a 6 inch pigtail to a mic connector
        and put a standard mic-jack on the pigtail

Option A or B is suitable if you only have one radio and mic.  I initially
preferred the universal option C where you simply solder back to back 
connectors and then run a 7 conductor cable of any length to the MIC-E.  
Conveniently, a standard 8 pin plug and jack will fit very nicely in a 
standard 1/2 inch to 3/8 inch copper reducing coupling.  Just saw it in 
half so you can place it over the connectors after they are soldered back-
to-back.  Drill a 1/4 inch hole in the side for the cable to the MIC-E.
Add lots of black tape to make it look nice.

But after my wife broke my back-to-back conector off with her purse, I now 
think that option D where you solder both the Mic-E and a 6 inch pigtail 
in parallel to a mic plug and put a companion jack on the pigtail is the 
safest way.  This assures that there is no additional stress on the mic
jack of your radio.  The following description uses the color code in the
central column of the note that comes with the 8 conductor cable from
PacComm.  There are three possible cable/color codes that may be shipped
with the Mic-E.  If yours is not the one in the center column, as verified
with an ohm meter, then change your colors appropriately.


   MIC JACK                                                 MIC PLUG

                  short 6" pigtail                          To Radio

   From Mic     >--green------------->                      Up Button
                >--violet--------------->                   Down button
                >--brown/shld------------*->                PTT/Radio gnd
                >--orange----------------|--*->             Rcv audio
                >--black-----------------|--|--*->          5/8 volts DC
                >--yellow----------------|--|--|--*->       Mic Audio
                >--blue------------------|--|--|--|--*->    Mic Gnd
                >--red----------------*  |  |  |  |  |  *-> PTT to radio
                                      |  |  |  |  |  |  |  
                                      |  |  |  |  |  |  |
   PTT into MIC-E     3  <---red------*  |  |  |  |  |  |
   PTT/Radio ground   2  >---brown/shld--*  |  |  |  |  |
   Receiver audio     4  >---orange---------*  |  |  |  |
   5/8 volts to Mic-E 1  >---black-------------*  |  |  |
   Mic Audio          5  <---yellow---------------*  |  |
   Mic Ground         7  >---blue--------------------*  |
   Mic-E PTT output   6  >---green----------------------*
                      8      violet not used   (I would parallel it to GND)
   Mic-E CONNECTIONS


INSTALLATION INSTRUCTIONS:

1) First you must determine how to power the MIC-E. If you will be using 
a GPS with its own power arrangements, then you may power the Mic-E from
the Mic jack power.  If you will be using the internal GPS or wiring GPS
power at the same time, you may as well use external power for the Mic-E.

   To use MIC power, measure the voltage at your MIC jack with a 330 Ohm 
load.  If it is between 5 and 7 volts connect directly to the Mic-E 
wirepoint WPX and install JP1.  If it is only 5 volts then also install
JP6 to bypass the internal 10 ohm resistor.  These arrangements will use 
only a Zener to regulate to 5 volts.  BE CAUTIOUS, HOWEVER, because this 
input has the regulator bypassed.  If 7.5 or more, connect to the Vin pin 
on the MIC-E.  Check all your radios with compatible connectors and plan 
to work with all of them...  If you do choose to mic circuit power, you
should also consider cutting and re-wiring the S2 power switch so that
it can also disconnect mic circuit power.  DO NOT BE TEMPTED to just jumper
mic circuit power to J1 so you can use the switch, because sooner or later
someone will plug in 12 volts to J1 and blow you PIC chip!

2) Interfacing ANYTHING to your microphone circuit is not trivial.  Any 
ground loop will add noise to the MIC audio (remember the alternator noise 
problems...)  Drawing 15 ma from the MIC circuit adds to this problem too.  
Separately powering the GPS from the 12 volt system and then connecting 
that data ground to the MIC encoder is also a potential noise source.  Be 
sure to use the isolated MIC ground as shown in the circuit.  Do not just  
connect this wire to just any-ole ground!  If you do, circulating ground 
currents will degrade the packet audio.  If your packets do not sound clean, 
you may have to power your MIC-E with a 9v battery to get clean power and 
audio... 


NOTES ON THE TAPR/PACCOMM MIC-ENCODER:

1)  The MIC-E was only designed to work with radios with separate PTT 
circuits.  Many HT's with combined PTT/MIC audio lines will not work.

2)  The Mic-E is not at true RS-232 voltage levels.  The data only swings
between 0 and 5 volts on output and may be incompatible with some RS-232
serial ports.  It should work fine with the GPS however.  If you are  
having consistent link failures with the MIC104.exe program try this:

            Mic-E output >-------/\/\/\/------*------> PC input
                                   1  k       |
                          -  *---/\/\/\/------*
                            ---    10 k
                             - 
                            ---  9 volt battery
                          +  - 
                             *-----------------------* Ground
JUMPERS

JP1  REGULATOR BYPASS - With this jumper ON, you can bypass the regulator
     chip when available MIC power is less than 7.2 volts.  External
     power must be fed to wire-point X.  In this case, you will be using
     the 10 ohm R4 and Zener diode D10 for regulation.  WARNING:  Do NOT 
     use this option for supply voltages greater than 7.5 volts or you may 
     cook everything.   DEFAULT is OFF.  See JP6.
    
JP2  AD0 INPUT - With jumper on pins 1 and 2, AD0 will read supply voltage
     in tenths of a volt.  Meaning 126 = 12.6 volts.  With jumper on 2 and
     3, AD0 reads external voltage on pin 1 of the extternal connector.

JP3  Not used on MIC-E prototype.

JP4  GPS INPUT - With the jumper in place, the GPS can be programmed
     externally from the DB-9

JP5  TBD - Default on pins 1 and 2.  

JP6  5 VOLT POWER - This jumper bypasses the 10 ohm series resistor in the
     Zener regulator circuit and relies on the source impedance of the MIC
     circuit power for current limiting.  WARNING:  Be sure to never use
     this jumper when supply voltages are above 5.8 volts.  DEFAULT is OFF.

JP7  TTL INPUT - With jumper on 1 and 2, you may input TTL data at wire
     point 12.  On position 2 and 3, data input is quasi RS-232 on pin 2
     of the DB-9 connector.  DEFAULT is 1 and 2.

JP8  GPS INPUT - With Jumper on, the internal GPS-20 is connected to the
     MIC Serial input port.  With jumper off, you may use the DB-9 for
     external serial connection to your PC for configuring the MIC-E.

J3   Mic-E LOADING - This jumper allows you to minimize the impedance
     loading of the Mic-E on your existing Mic Circuit.  Use the highest
     value resistance that still gives suitable packet audio level without
     loading down the voice audio.  DEFAULT is on pins 3 and 4 for 10K.

OPERATIONS:  My initial guess at a POSperiod is about 1 minute and an auto 
period of about 4 minutes and a QUIET time of about 10 seconds.  I usually 
leave AUTO OFF so that I wont key up the repeater unnecessarily.  I also   
always have PATHS set to zero so that the packet is as short as possible.
Since no one is really tracking me yet, to put out a good posit on the APRS 
network, however, I just dial in my 145.79 memory channel, set PATH to
3 (RELAY,WIDE,WIDE) and kerchunk the mic, and listen for the digipeat.  If 
I hear it, then I got in and I'm on the maps!.

   AUTO has two uses.  On a voice repeater you might set QUIET to long
enough to be sure the repeater is really not BUSY before you kerchunk it.
But if you use AUTO on the APRS packet channel, then you want QUIET to
be ZERO so that it acts only for colision avoidance.  If QUIET is non
zero and you have a busy APRS channel it may never transmit!.  You can
override this if you need to, by simply turnning the volume down, but
then you dont have colision avoidance.  So this is a tradeoff.

    Once the REPEATERS mute the packets, then QUIET might be able to be set 
to zero on the voice repeater too and this will solve this problem...
Just be sure to never turn your radio volume down on a REPEATER if you
have AUTO on, or you will BRAAAP other people...

   You may want to add a tiny LED on the MSB of the path bit just so you
cam identify its position in the DARK.  Just rotate the PATH switch till
the LED goes OFF and you are at the 0th path position.  You may do the
same thing with the MSG switch if you add a 1K pull up and are willing
to giveup the dual use of AD1 as an analog input also...  Maybe you could
use a high gain inverted PNP transistor with the 470K resistor going to
its base as a current amp to pull-up" the LED without severly loading the
analog usage...  

    Without these night time vision aids, you will be in the dark whenever
you diddle the switches such as going between 145.79 and voice...

-----------------------------------------------------------------------

APRS REPEATER NODE TNC:  

    This special TNC NODE is designed to be intgrated into typical amateur 
voice repeaters.  The TNC performs a number of special functions to fully 
implement the APRS LOCATOR SYSTEM:

   * It has true DCD to distinguish between voice and data for muting
     the repeater audio during packets
   * It digipeats all position reports from the repeater receiver to the
     dedicated APRS digital channel
   * It implements the APRS Directional Digipeating algorithm
   * It implements the APRS WIDE-N digipeater algorithm for OMNI packets
   * It appends ADDText (usually the rptr freq) to the end of all packets
     ("Via 146.940") 
   * It an external carrier detect for the APRS packet channel for
     true CSMA effeciency, typically just a connection to the squelch
  
Notice that although the APRS REPEATER NODE function only listens on the
voice repeater input and only transmits on the digital APRS packet 
frequency, it must also have a secondary carrier detect on the APRS packet 
channel to avoid collisions.  This special APRS node function is NOT 
involved in any further routing on the APRS digital channel (I mean that 
it does NOT serve as a general purpose APRS digipeater on the digital 
channel).  All it does is to insert the appropriate directional or OMNI 
digipeater path and digipeat the packet.  This distinction, of course, 
is only a functional distinction, since APRS digipeater functions can be 
co-located, or even built into the same NODE box as long as dual digital 
receiver channels are maintained.


REPEATER MUTING:  Since the  acceptance of the POSIT-PACKET on voice
repeaters will be determined by the minimization of the BRAAAAAAP sound
on the repeater output, the DCD and subsequent muting of the repeater
are important.  Muting the repeater output is easy if use the signal from 
the DCD LED on the TNC to implement a 20 dB attenuation in the audio line 
to the repeater transmitter.  I think a 10 to 20 dB attenuation is 
appropriate.  If it is completely  muted, then no one will know about your 
new toy, and more importantly, the DCD may occasionally mute some sylables 
of some voices.  The problem is that the TNC must have the add-on True-
DCD so that it responds only to packets and not voice.  See the following
section.


USING ANY TNC AT THE REPEATER:    Unitl the special APRS NODE is available, 
you can use any TAPR-2 compatible TNC with the add-on True DCD such as the 
PacComm Tiny-2.  Just connect its audio input to the repeater 
input receiver and connect its TX audio and PTT to a small 1 watt XMTR 
on 145.79.  Use the output of the add-on True-DCD circuit to mute the
voice repeater transmitter.  This will work fine, but is not going to 
avoid collisions.  It is better to have a transceiver on 145.79 and use its 
squelch to drive the external Squelch DC signal on the TNC to implement 
CSMA.  Be sure to isolate the add-on True-DCD output from the Squelch
output so that packets on the Packet channel do not also MUTE the voice
repeater!

NOTE:  You cannot use the KPC-3 TNC set to software DCD, since it then
IGNORES the external DCD defeating this dual carrier detect capability.  




NOTES:   Notice that the APRS REPEATER NODE will also work on the digital
channel!  In other words, the APRS REPEATER NODE algorithms can also be
running simiultaneously in all of the APRS DIGI's so that the APRS compressed
format will be picked up directly on the digital channel.  These original
packets are distinguishable because they DO NOT have an original DIGI field.
Once a NODE processes them and adds the DIRECTIONAL or WIDE routing, they
will be forwarded as usual.  Notice that the NODE hardware can actually do
both functions as long as dual digital receive channels are provided.


MIC-ENCODER ASSEMBLY NOTES:  (OBSOLETE.  THIS WAS BUILDING IT FROM A MIM)
                             ********************************************

    The MIC-ENCODER is the original APRS TELEMETRY TNC transmitter on a
chip (MIM Module) with different code for the  MIC-ENCODER algorithms.  The
following partial schematic shows how the MIC-ENCODER evolved from the MIM: 


 MICROPHONE                                                      RADIO
 ----------                                                     --------

 MIC >-----------------------------------------*----------------> AUDIO
                                         47k   |
                                     *--/\/\/--*  *-------------> MIC gnd
                                     |            |     
 +8v <----------*--------------------------------------*--------< +8 V
                |                    |            |    \ 1k
                |              D1    |            |    /
 PTT >---*---------------------|<----------------------\------*-> PTT
         |      |                    | MIC audio  |    /      |
         |    |-|----------------------|          |    *      |
         | D2 | *                    * | MIC GND  |    V  LED |
         *-|<-|-*    MIM MODULE      *-|----------*   ---     |
   PTT in     |                        |               |  D3  |
              | *               *    * |  PTT OUT      *--|<--*
              |-|---------------|----|-|    5.6K     |/c  
                |               |    *----/\/\/\-----|   Q1 NPN
                |    *----*-----*                    |\e
                |    |    |     c\|  Q2 NPN            |
                | S1 *    |       |--------*-----||-------------< RCV AUDIO
                |  \      |     e/|        |   .2 uf   |
                |    *   ===    |          -           |
                |    |    | 6uF |          ^ D4        |
                |    |    |     |          |           |
 GND >----------*----*----*-----*----------*-----------*--------> GROUND


CIRCUIT DESCRIPTION:  D1 isolates the microphone PTT from the radio PTT
input so that the Mic-E can key the PTT line while also sensing the MIC
PTT condition.  D2 prevents the MIC-E from grounding the PTT lead when
the MIC-E is turned off.  Q1 is an open collector PTT transistor.  The
LED shows when the Mic-E is holding a PACKET, waiting for the user to 
release the MIC PTT.  D3 isolates the LED from the mic PTT.  The 47K
minimizes circuit loading and the isolated MIC ground is connected to the 
lower end of the MIM audio pot to minimize ground loop noise.  Q2, D3 and 
the lower two caps are an audio rectifier to drive the HOLDOFF input to 
the MIM when the radio is in use.  S1 is the AUTO switch.  When OFF, it 
asserts hold off, so that the MIC-ENCODER will never auto-initiate a posit 
on its own.  Bits D2 to D8 connect the PATH and MESSAGE switches and A5
is the PERIOD adjust pot as follows:
                                             A3 (was A5 in early MIM/MIC's)
               D8 D7 D6 D5 A1 D4 D3 D2       A5    +5v
               *  *  *  *  *  *  *  *        *      *
               |  |  |  |  |  |  |  |        |      |
               -----------------------       |      |
               |          |          |       |      /
               |     7    |     7    |       *----->\ 10k
               |  P A T H |   M S G  |              /
               -----------------------              \
                     |          |                   |
                   -----      -----               -----
                   ////       ////                ////

SERIAL PORT FOR GPS AND CONFIGURATION:  All users should consider using
the APRS standard 1/8 inch stereo phone plug/jack for their serial
data port on the MIC ENCODER and other small stand-alone-trackers.  
The phone plug is small, readily available, and is compatible with
the nominal mono 1/8 inch phone plug found on many GPS units:

    GPS UNIT or PC LAPTOP                 MIC-E or embedded TNC
    ---------------------                 ----------------------
    mono or stereo PLUG                   1/8th inch stereo JACK
    
    TXD (data out)   --------------------> TIP    
    RXD (data in )   <-------------------- RING   
    GND              *-------------------* SLEVE

To help remember, just think of the DATA comming out of the male plug tip.
This applies to the GPS by itself or to the laptop used to CONFIGURE the
stand-alone tracker.  By using a "closed-circuit" jack, an internal GPS
can be normally connected to the internal MIC-E or TNC, but plugging in
the LAPTOP opens that circuit and connects the laptop to the TNC...

9 PIN CONNECTOR OPTION:  Although the Mic-Encoder uses a standard DB-9 for 
its external connections, only pins 2,3, and 5 are the serial port for 
the GPS and for configuration with a laptop.  Most of the other pins are
defined as follows:

    Pin 1   Analog input #1
    Pin 2   TXD    Data to the PC
    Pin 3   RXD    Data from the PC or GPS to the Mic-E
    Pin 4   V+     Useful for powering the GPS
    Pin 5   Ground
    Pin 6   Analog input #2 (shared with SSID/DIGI select switch)
    Pin 7   n/c
    Pin 8   Analog input #3 (Used as PERIOD POT)
    Pin 9   Analog input #4 (suggested for internal temp)

The analog inputs should be protected with a 100 ohm series resistor and
a 5 volt zener to ground.  These were NOT on the beta test units, so the
analog inputs were isolated from the connector.  If you re-install them, 
be sure to add this protection.  The inputs were placed on pins in the DB-9e
that should be safe for cables used on most computer serial ports.

TEMPERATURE MEASUREMENTS:  By proper selection of 2 resistor values and
2 to 4 diode voltage drops, you can easily make one of the Digi-Key
$2 thermisters read out temperature in degrees F.  For details, run the 
MIC-TEMP.BAS program.  It is suggested that AD-2 be used for internal
temperature just for consistency with the default APRS Telemetry Display.
