TELEMTRY.txt 7.4e APRS TELEMETRY SYSTEM Using the Micro.Interface.Module (MIM) The MIM module is a complete telemetry TNC transmitter on a chip. It has a serial data port, 5 analog and 8 digital telemetry inputs. It outputs PTT and transmit audio AX.25 tones. The MIM was developed by Carl Wick, N3MIM, as a very simple, light-weight, throw-away module for experimental balloons. He has teamed up with Will Clement and refined the chip into a very useful APRS packet tool. The only external components besides the sensors themselves, are a transmitter and optional GPS card and battery. A 0.3 cu in. 800 mw xmtr is available from Agrelo Engineering too! ___________ Analog 1 --O| |O-- 5 volts Analog 2 --O| |O-- Ground Analog 3 --O| |O Analog 4 --O| M.I.M |O Analog 5 --O| |O-- Xtal Rcv Audio --O| AX.25 |O-- Xtal NMEA Serial --O| |O Input bit 1 --O| Telemetry |O input bit 2 --O| |O-- AX.25 out input bit 3 --O| Chip |O-- PTT input bit 4 --O| |O input bit 5 --O| |O input bit 6 --O| |O input bit 7 --O| |O input bit 8 --O| |O ------------- EXTENDED LIFE OPTION: For extended operation (up to a year or more), the MIM can be configured to go to sleep between reports. A single set of AA Alkaline batteries could power the MIM and 1 watt transmitter for a YEAR at one report every 30 minutes. Additionally, the power to the GPS can be programmed separately to allow time for obtaining a current fix. Assuming a worst case of the GPS needing 15 minutes per fix for a full sky search, this could result in a system that could "check its position" once a day, report its position, telemetry and status every 30 minutes using a 1 watt XMTR for a YEAR on a single set of alkaline D cells. APRS TELEMETRY RECEIVING SYSTEM: In order to make the APRS Telemetry page show real engineering values and units, APRS uses on-air packets to distribute the Telemetry labels, units, and equations. This means that APRS does not need to be progammed for each different application. In the case of a one-time balloon launch, any ground station that knows the telemetry definitions only needs to send four one-line BULLETINS. THe first one defines the telemetry labels, the second defines the units, the third defines the telemetry equations, and th forth defines the project name and digital bit definitions. 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. The last 16 values are displayed. 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 hours 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 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) Tracking wildlife or packages 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 800 mw model is now out! See more cheap transmitters in the GPS.TXT file. ORDERING YOUR M.I.M. SYSTEM: Oder the MIM from Clement ENgineering, Inc. PO Box 1086 Severna Park, MD 21146. Phone 410 268-6736, FAX: 410 268-4612. Email wiclement@aol.com. NOTE, THis is a new model from the original 4 channel prototypes. If you have one of the originals, it is only on-air compatible with APRS versions APRS74b or earlier.