TELEMTRY.txt 7.4c         APRS TELEMETRY SYSTEM
                   Using the Micro.Interface.Module (MIM)

The MIM module has CHANGED since first introduced at Dayton 95.  It now has
5 Analog channels and 8 digital bits.  Also it has a serial port for NMEA
GPS data so that it can send its POSIT as well as telemetry.
NOTE:  There were only 4 of the original 4 channel models sold, so those
units must use APRS74b or earlier to decode the old telemetry format.

The following text represents the new MIM module but the physical detail 
and PIN outs are still preliminary

      Carl Wick, N3MIM, has developed a simple, yet powerful Micro-Interface-
Module that can be used as a single chip APRS telemetry system.  Although the
intent of his original design was to make a very simple, light-weight, throw-
away module for experimental balloon flights, his design has now evolved into
a very useful APRS packet tool.  Using a single chip microprocessor, he has
implemented a complete TNC (transmitter only) on a chip.  This chip has five
analog inputs, eight digital bit inputs, a receive audio input (for propoer
CSMA operation) and outputs PTT and AX.25 audio using digital synthesis.  The
only external components besides the sensors themselves, are a crystal and a
transmitter.  A 0.2 cu in. 500 mw xmtr is available too!  The pin-out follows:

                    _____________
        Analog 3 --O|           |O-- Analog 2    THIS SCHEMATIC IS NOT
        Analog 4 --O|   M.I.M   |O-- Analog 1    NOW CORRECT!
       Rcv input --O|           |O-- Xtal
           reset --O|   AX.25   |O-- Xtal
           Gnd   --O|           |O-- 5 volts
     Input bit 1 --O| Telemetry |O-- AX.25 out
     input bit 2 --O|           |O-- AX.25 out
     input bit 3 --O|   Chip    |O-- PTT
     input bit 4 --O|___________|O-- Input bit 5


APRS TELEMETRY RECEIVING SYSTEM:   Any telemetry system requires a table of
equations and labels to make the values useable at the receiver site.  The
problem with most experimental telemetry systems, is that the receiver system
must be tailored for every new application.  In the case of a one-time
balloon launch, (or any experiment assembled to meet a schedule) the
equations are not usually available until just hours or minutes before
launch.  This means that it is next to impossible to distribute the equations
and parameter definitions to a large number of tracking stations and to be
able to have receiving telemetry software ready to go.

      For this reason, APRS has been designed to serve as a general purpose
telemetry tracking system for the M.I.M.  Using APRS it is possible to
transmit the telemetry equations, parameter definitions and channel units IN
REAL TIME!  Once any APRS station receives these parameter transmissions, it
is then ready to receive and to display the real-time telemetry values in the
proper engineering units.  The TELEMETRY page is displayed using the alt-T
command.  Hitting this command causes APRS to scan the READ MAIL screen
looking for the telemetry equations, and then to scan the ALL_BEACONS pages
looking for TELEMETRY values.  Up to 16 samples are displayed per page, for
a total of 75 samples.  The TELEMETRY samples are saved in the normal LOG
files.  A sketch of the APRS telemetry display is shown below:


APRS TELEMETRY FOR XYZ BALLOON LAUNCH

SER TIME Battery  AirTemp BTemp Pres  Altud Camra Par Sun 10m ATV 5th 6th etc 
NUM      volts    deg.F   deg.F Mbars K ft  BIT   BIT BIT BIT BIT BIT BIT
--- ---- -------- ------- ----- ----- ----- ----- --- --- --- --- --- ---
101 1215  12.8     86      85    999    0    ...  ... ... ... ... ... ...
102 1216  12.8     86      85    999   1000  ...  ... ... ... ... ... ...
103 1217  12.6     87      87    998   2000  ...  ... ... ... ... ... ...
104 1218  12.4     84      80    980   4000  clik ... on  on  hi  ... ...
105 1219  12.3     80      76    900   8000  ...  ... ... on  hi  ... ...
106 1220  12.1     75      70    850  16000  ...  ... on  on  ... ... ...
107 1221  12.0     70      65    800  32000  clik ... ... ... ... ... ...
108 1222  12.0     65      60    730  64000  ...  ... on  ... hi  ... ...


    Notice that the M.I.M module transmits a value for each of its five
analog channels and each of its eight digital bits once every sample time. 
The sample periodicity can be set from any value from 1 second to 16 minutes 
depending on the application.  Each sample includes a unique serial number.  
In addition, not only can the parameter name, units and equations be 
specified for each of the analog channels, but the word to be associated 
with either the 0 or 1 value of each digital bit can also be specified.

     To configure all APRS stations to properly decode the telemetry from the
M.I.M module, the net control station (or any other designated station in the
APRS network) needs to transmit the proper parameter definition packets.
These packets are transmitted as APRS messages TO the CALLSIGN of the M.I.M
module.  If the M.I.M module is using the callsign of N3MIM, then the
parameter definition station would send the following four messages:

To N3MIM:PARM.Battery,BTemp,AirTemp,Pres,Altude,Camra,Chute,Sun,10m,ATV
To N3MIM:UNIT.Volts,deg.F,deg.F,Mbar,Kfeet,Clik,OPEN!,on,on,high
To N3MIM:EQNS.0,2.6,0,0,.53,-32,3,4.39,49,-32,3,18,1,2,3
To N3MIM:BITS.10110101,PROJECT TITLE...

The PARM format specifies the name of each of the 13 parameters.  The UNITs
format specifies what units are to be displayed, and for the digital bits,
show what label is associated with the digital condition.  The parameters and
units for the first two can be up to 9 and 8 characters respectively, the 
next 3 can be 6 characters, the first three BITS can be 5 characters and the
final 5 can be four characters each.   The EQNS format has three coeficients 
for each of the five analog channels.  The BITS format specifies either a 1 
or a 0 for each of the five digital channels to indicate which state is 
associated with the indicated label.  This permits the payload designer to 
use 1's or 0's as convenient with his circuity without being forced to always 
use 0 for OFF and 1 to mean ON.  A title can also be included in the BITS 
definition which will be used by APRS to title the TELEMETRY page.  The three 
values for each of the analog channels are the coeficients of a quadratic 
equation:

  Final value = A*X^2 + B*X + C  Where X is the M.I.M transmitted value

FORMAL SPECIFICATION:  The specific format for the TITLE, PARM, UNIT, and EQNS
message packets are shown below.  They are entered as messages to the address
of the MIM module:

  PARM.P1,P2,P3,P4,P5,B1,B2,B3,etc    Where Pn and Bn are the parameter names

  UNIT,U1,U2,U3,U4,U5,L1,L2,L3,etc    Where Un are the units for analog ports
                                      and Ln are the labels for the bits

  EQNS,A1,B1,C1,A2,B2,C2,A3,B3,C3,etc Where the An,Bn,Cn are the coeficients 
                                      for each of the five analog channels, 
                                      
  BITS.XXXXXXXX,Title-up-to-23-chars  The x's specify the state of the bits
                                      that match the BIT Labels.

  T#sss,111,222,333,444,555,xxxxxxxx  This is the on-air format for the UI
                                      packet, where sss is the serial number
                                      followed by the five 3 digit analog
                                      values and the eight binary values.
                              

APPLICATIONS:

   1)  Balloon payloads using only party balloons, not needing the big
       WX balloons and all the paraphanalia.

   2)  TRAFFIC monitoring MILE posts!  This is a neat idea!  Given that HAMS
       will be commuting with APRS moving Map displays, why not build a match
       box sized traffic SPEED detector (solar powered MIM module) that can be
       stuck on the side of a highway pole ?  Via a $1.29 crystal MIC from
       radio shack, use DSP to figure out the speed of the traffic based on
       audio analysis!  Beacon this SPEED once every two minutes at about 10
       mW.  The beacon will, of coure, include the LOCATION of the device.
       What the APRS commuter sees on his MAP is these MILE posts ahead of him
       showing traffic speeds!  He can then decide on alternate routing!

            We have plenty of room in the MIM to add this DSP (maybe), IS
       THERE ANYONE OUT THERE THAT IS INTO DSP THAT CAN DETERMINE THE
       ALGORITHM TO DETERMINE SPEED FROM THE AUDIO OF TRAFFIC??????????
       (or the amplitude fluctuations of a photo cell?) Even cheap X band
       doppler motion detectors are possible, since they only need to turn
       on briefly to get a speed measurement.  This thing has to be VERY small
       and low power to be able to be SOLAR powered and able to be COVERTLY
       installed with out a lot of STATE HIGHWAY bureaucracy.

LOW POWER TELEMETRY TRANSMITTERS:  To complement this less than ONE-CUBIC
inch MIM telemetry system, Agrelo Engineering in NY makes a 1.5 x 0.5 x 0.25
inch 2 meter transmitter for $99.  It outputs 500 mW at 6 volts 140 ma and
120 mW at 3 volts 50 ma.  A new model is now out with more than a Watt!
See more cheap transmitters in the GPS.TXT file.


ORDERING YOUR M.I.M. SYSTEM:   All of the MIM parameters are field program-
mable in NOVRAM.  Please use the following form when ordering your MIM.
(DO NOT ORDER YET!   THIS IS PRELIMINARY!)

   Callsign   _______________________

   APRS V#    _______________________

  

