TELEMTRY.TXT APRS TELEMETRY SYSTEM =========================================================================== Document version: 8.3.8 Document dated: 27 Mar 99 Author(s): Bob Bruninga, WB4APR ABSTRACT TELEMTRY.TXT: Using the Micro Interface Module (MIM) for APRS telemetry. The MIM module is a complete telemetry TNC on a chip. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ See Mic-E.txt for how the MIM chip is used in the APRS Mic-Encoder See Mic-Lite.txt for how to make the MIM into a simple Mic-E Kantronics also uses the MIM type Telemetry format for its KPC-3+ and KPC-9612+ TNC's. Simply activate the periodic telemetry packet using the TELEMETRY command to the TNC. See format below. 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 Dr. Carl Wick, N3MIM, as a simple, light-weight, throw-away module for experimental balloons. WB4APR modified it for Mic-E operation and Dr. Will Clement refined it into a commercial product. It is now sold by APRS Engineering LLC at the address below. The only external components besides the sensors themselves, are a transmitter and optional GPS and battery. EXTENDED LIFE: For extended operation (up to a year or more), the MIM can be turned on/off with an external timer 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. MODULE INPUTS OUTPUTS ___________ Analog 1 --O| |O--> PTT to XMTR Analog 2 --O| |O--> Audio to XMTR Analog 3 --O| |O Analog 4 --O| M.I.M |O<-- Rcvr Audio Analog 5 --O| |O<-- GPS NMEA data Input bit 1 --O| Telemetry |O input bit 2 --O| |O input bit 3 --O| Module |O 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 ------------- MIM PACKETS: The mim can operate in either MIM mode or MIC mode. Here are the packets in each mode: MIM MODE: STATUS packet transmitted every N seconds POSIT packet transmitted every P seconds TELMETRY packet transmitted every T seconds CWID transmitted every C seconds Mic MODE: POSIT packet every P seconds STATUS text apppended to posit every P/S seconds TELM telemetry appended every P/T seconds MIM TELEMETRY: Each telemetry value is a decimal number between 000 and 255. The user can adjust his sensors to meaningful values, or the telemetry equations can be modified on receipt. The on-air packet telemetry format is as follows: T#sss,111,222,333,444,555,xxxxxxxx where sss is the serial number followed by the five 3 digit analog values and the eight binary values. BATTERY VOLTAGE: Just a simple 10k and 2.4k resistor divider connected to channel 1 will give you a battery voltage reading in tenths of a volt. Thus, a reading of 138 would mean 13.8 volts. For precision, you might want to replace the 2.4K resistor with a pot to tweak the reading to an exact calibration. TEMPERATURE MEASUREMENTS: Similarly, by proper selection of 2 resistor values and 2 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 draws the schematic and allows you to select the proper resistor values. It is suggested that AD-2 be used for internal temperature just for consistency with the default APRS Telemetry Display. TELEMETRY EQUATIONS: The real beauty of the APRS telemetry system is that you are not limited to specific calibrations as used above. APRS can display any other telemetry values acording to any specific quadratic telemetry equation. For the ultimate in flexibility, APRS can receive on-air packets to define the Telemetry labels, units, and equations. Thus it does not need to be progammed for each application. These paramaters may be transmitted to all APRS stations live via four one- line BULLETINS. The first one defines the telemetry labels, the second defines the units, the third defines the telemetry equations, and the forth defines the project name and digital bit definitions. LIST-TELEMETRY. To see telemetry data in APRSdos, hit the LIST-TELEMETRY command. Hitting this command causes APRS to scan the TRAFFIC page looking for telemetry equations, and then to scan the LIST-LOG page for any TELEMETRY values. 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... NUM volts deg.F deg.F Mbars K ft BIT BIT BIT BIT BIT BIT BIT --- ---- -------- ------- ----- ----- ----- ----- --- --- --- --- --- --- 101 1215 12.8 86 85 999 0 ... ... ... ... ... ... ... 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 ... ... To configure all APRS stations to properly decode the telemetry from a M.I.M module, one station transmits the proper parameter definition packets TO the CALLSIGN of the M.I.M module. For example of N3MIM's MIM: 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 UNIT format specifies what units are to be displayed, and what label is associated with the digital condition. The BITS format specifies whether a 1 or 0 indicates the indicated label and also the project Title. The EQNS format has three coeficients for each of the five analog channels. 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. PARAMETER NAMES: Due to the 80 character screen width in DOS, each parameter has a fixed NAME/UNITS length. The lengths for the 5 analog channels are 7, 6, 5, 5 and 4 characters. The lengths for the 8 digital bits are 5, 4, 3, 3, 3, 2, 2, and 2 characters respectively. So you may need to decide early on what channel to use for what purpose based on the number of characters available in the display... DEFAULTS TO APRS Mic-ENCODER: Since the predominant application of the MIM module is in the APRS Mic-Encoder, the default telemetry parameters and units for the Mic-E are normally displayed. These will go away if any on-air parameters or equations are received... APPLICATIONS: 1) Balloon payloads using only party balloons (not big ones) 2) Tracking wildlife or packages 3) Small stand-alone trackers 4) Model Aircraft 5) Keeping track of your kids. 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 MIM: The MIM is now being sold by students at Stanford University...