Alt15K/WD User`s Manual
Contents
1. retrieved from nonvolatile EEPROM memory and reported This feature allows the user to determine a flight s altitude even if the rocket cannot be recovered before the battery is depleted approxi mately 24 hours After the previous flight altitude is reported the altimeter waits 15 seconds for the electronics to stabilize then emits a periodic beep to indicate readiness for launch 1 Next the ground level elevation is sampled every 100 milliseconds and the microprocessor looks for a sudden decrease in pressure signifying a rapid increase in altitude launch detection When the altitude exceeds a preset threshold 80 feet above the ground reading launch is detected The previous 8 altitude samples are saved to logging memory and additional samples are added every 100 milliseconds for the duration of the flight While awaiting launch the ground level will be updated if a slow change is detected to compen sate for thermal and ambient barometric pressure drift The altitude results are inspected during flight to determine apogee peak altitude When the derived rate of ascent decreases to zero apogee is detected and the peak altitude reading is stored in nonvola tile memory for later retreival Altitude readings continue to be taken and saved in logging memory during descent When the altitude is less than 300 and the sink rate is less than 4 feet per second data collection is terminated At this point the peak altitude is re2. feet AGL 0 3 reading 4 OC to 70C 10 Warranty All assembled PerfectFlite products include a full three year 36 month warranty against defects in parts and workmanship Should your PerfectFlite product fail during this period call or email our Cus tomer Service department for an RMA number and information about returning your product The warranty applies to the altimeter only and does not cover the rocket motor or other equipment This warranty does not cover damage due to misuse abuse alteration or operation outside of the recommended operating conditions included with your product Broken pressure sensor diaphragms due to puncture or exposure to ejection charge pressure hot gasses are NOT covered under this warranty Liability Due care has been employed in the design and construction of this product so as to minimize the dangers inherent in its use As the installation setup preparation maintenance and use of this equipment is beyond the control of the manufacturer the purchaser and user accept sole responsibility for the safe and proper use of this product The principals employees and vendors of the manufacturer shall not be held liable for any damage or claims resulting from any application of this product If the purchaser and user are not confident in their ability to use the product in a safe manner it should be returned to the point of purchase immediately Any use of this product signifies acceptance of
3. strip immediately prior to placing the altimeter in the rocket to turn it ON A variation on this idea can be used if the altimeter will be located in an inaccessible location inside the rocket or if the payload compartment cannot be closed quickly upon activation of the altimeter Substitute a piece of monofilament fishing line for the plastic strip and route it out through the pressure sampling hole With the line in place the altimeter will be OFF When the rocket is ready to fly pull the exposed line out to activate the altimeter make sure you wait for the readiness beeps before launching plastic tab switch plastic cord switch Installation Your altimeter needs to be installed in a separate payload compart ment sealed from the pressure and heat of the ejection charge gasses It is not OK to tie it to the shock cord and pack it in with the chute The high pressure and heat encountered during ejection would damage the delicate pressure sensor s diaphragm A typical payload compartment consists of a section of body tube behind the nosecone with a sealed tube coupler connecting it to the main body tube see figure 2 Some rockets already have such a payload section and one can be added easily if yours does not Loose fit Glue Tight fit Wadding Sampling hole Altimeter Figure 2 Installation in a payload compartment Install the altimeter in the payload section with the pressure sensor facing up
4. Alt15K WD User s Manual LES A AA 1 BENGINE a m T n i i y bl 3 DURACELE A ee E e 2123 mi lj p o PerfectFlite Alt15K WD User s Manual A subminiature altimeter with audible peak reporting and full flight logging download capability Perrectriite 15 Pray Street URL www perfectflite com Amherst MA 01002 Sales sales perfectflite com Voice 413 549 3444 Support support perfectflite com FAX 413 549 1548 Contents ds 1 Theory of Operation eesseesooesoeesocssocesosesoeesoessosesos 1 Preliminary Setup Getting to know your altimeter scscscecsssscccscscscccscccccececececs 2 Powering the altimeter casasasssvcdsscecsscdecccecsescessesesesesescsdedeveess 3 Installation Payload compartment Setup csccscssscscccccccccccscsccccscscscscscsees 4 Sampling hole Size chark acc 5 Numerical reporting method scccccccsscscscsccccscccccscscccscscsces 6 Operation SEQUENCE OF CVENIS asiewesessacscscva eves sa vuvenasessescatacseneeeeusesesesass 7 Computer CONMECNON sssisisissiescssedcacscccsecacsoessesssscssssesserenescos 8 Ground sessed oa roere aE NNN 9 CGUMOMS aiii 10 Specifications ii ii 10 Laela Eo Ti p Er T E E EET 11 Congratulations on your purchase of the new Alt15K WD altimeter Please read these instructions carefully before attempting to use the altimeter to insure safe and successful operation Your new altimeter provides several useful functions Y Peak altit
5. Installing it in this orientation will reduce the stress on the battery spring during acceleration Use pieces of foam rubber in front of and behind the altimeter to prevent it from shifting under acceleration and deceleration The altimeter will slide easily into 18mm BT20 size body tubes and a sleeve made out of standard foam pipe insulation can be used for larger size tubes Make sure that your foam rubber pieces do not block the path from the air sampling hole to the altimeter s pressure sensor element A channel can be cut in pipe insulation for this purpose make sure that the channel lines up with the sampling hole and the sensor s air inlet Your payload section should close securely so that the altimeter is not ejected upon motor burnout deceleration or chute deployment shock When installing the Alt15K WD in larger rockets it may be easiest to add a short 3 long section of BT20 tube with padded end plugs for the altimeter to ride in The short BT20 tube could be glued to the inside of the larger airframe or to a plywood mounting plate Don t forget to incorporate vent holes in the inner tube to allow external air pressure to get to the altimeter You must drill a clean edged hole in the payload section to allow outside air pressure to be sampled by the altimeter This hole should be as far away from the nosecone and other body tube irregularities as possible 3X the body tube diameter or more to minimize pressure
6. aunch it is likely that closing the payload compartment will inadvertently trigger the altimeter and produce an erroneous reading This is due to the fact that when you close the compart ment you will pressurize the interior of the compartment and when the pressure diminishes through the sampling hole the altimeter will interpret this as a rapid ascent launch If it is not convenient to install the altimeter in the time allotted you can arrange an external activation switch with monofilament fishing line as discussed under Powering the Altimeter When you recover your rocket the altimeter will be beeping to report the peak altitude attained Since this reading is saved in nonvolatile memory you can safely turn the altimeter OFF at any time If you want to retrieve the altitude reading at a later time simply turn the altimeter back on and the altitude will be reported again 7 Computer Connection The altimeter can be connected to a computer via the appropriate cable kit and software This will allow you to retrieve the entire saved flight profile generate an altitude vs time graph and save the data to disk The data are transferred in a proprietary binary format with block acknowledge so a terminal emulator program can NOT be used Suitable MacOS and Windows compatible software is available on the PerfectFlite web site for free download The altimeter s data connector provides and expects TTL level signals as described in
7. disturbances being created by turbulent airflow over the body tube Sand the area around the hole as necessary to eliminate flashing or raised edges Exact sizing of the hole is not critical refer to the table below for suggestions While not strictly necessary the single sampling hole can be replaced by several smaller holes distributed around the airframe s circumfer ence This will minimize the pressure variations due to wind currents perpendicular to the rocket s direction of travel 047 3 64 078 5 64 156 5 32 219 7 32 344 11 32 3 1 Table 1 Payload Section Size vs Sampling Port Hole Size 5 Numerical Reporting Numbers are reported as a long beep separator followed by a pattern of shorter beeps All numbers are reported using up to five digits a series of beeps for the first digit tens of thousands of feet a short pause another series of beeps for the next digit thousands of feet etc Leading zeroes are suppressed 1 582 feet would be represented with four digits not five digits as in 01582 Ten beeps are used to indicate the number zero if zero beeps were used you would not be able to differentiate between 2200 feet and 22 feet As an example 12 560 would be reported as long beep pause beep pause beep beep pause beep beep beep beep beep pause beep beep beep beep beep beep pause beep beep beep beep beep beep beep beep beep beep long pause Repor
8. he readings will be rejected If you generate a rapid spike in the jar s vacuum not representative of actual rocket flight the data will be recorded properly for download but the apogee reading will be incorrect Cautions e Donot touch circuit board traces or components or allow metallic objects to touch them when the altimeter is powered on e Do not expose altimeter to sudden temperature changes prior to operation e Donot allow strong wind gusts to enter the airframe pressure sensing hole this could cause premature launch detection e Do not allow direct sunlight to enter the pressure sensor s vent hole this could cause premature launch detection e Do not allow the altimeter to get wet Only operate the altimeter within the environmental limits listed in the specifications section e Check battery voltage before each flight and replace if low e Do not rupture pressure sensor diaphragm with excessive pressure or sharp object e Always follow proper operational sequencing as listed in preflight checklist Specifications Alt15K WD dimensions weight operating voltage operating current Serial data format Serial data rate maximum altitude resolution launch detect altitude accuracy operating temperature 2 45 L x 0 55 W x 0 55 T 14 grams with battery 12V nominal 6V 16V 1 3 ma typical 8 data no parity 1 stop binary 9 600 bps 15 000 feet MSL 4 SL 6 O15KMSL 80
9. ported continuously at ten second intervals via a sequence of beeps Getting to Know Your Altimeter Refer to figure 1 below to identify the following items A Audio beeper B Serial data I O connector C Battery holder note polarity D Pressure sensor C D A B a i DURACELL A PLE ALCALING th 1 4 E i 21 29 a I Figure 1 Parts identification 2 Powering the Altimeter The altimeter is powered by a standard 12 volt N size remote battery Appropriate part numbers are Duracell MN21 23 GP A23 Energizer A23 and Radio Shack 23 144 Observe polarity when installing the battery to prevent damage to the altimeter If the altimeter will not be used for an extended period of time the battery should be removed to keep tension off the battery holder s negative spring terminal If high G flights are expected a small wad of aluminum foil can be placed between the battery spring and the negative battery terminal to increase contact force This will help prevent loss of power during hard acceleration or decelleration Since the acceleration force will typically be greater than deceleration at burnout having the spring end of the battery holder facing forward in the rocket will help too A small strip of plastic can be inserted between the battery positive terminal and the battery holder to create a simple power switch This will keep the altimeter OFF while it is in place Simply remove the
10. ted as EN beep beep beep beep beep beep beep beep beep beep MOM MOM NS MEN beep beep beep beep beep beep beep beep beep Table 2 numerical beep sequences 6 Operation To insure proper operation of your altimeter you must follow a specific sequence of events If you launch before the altimeter is ready ground level will not be sampled properly and the altitude readings will be wrong Sequence of events Prepare your rocket and install the engine before setting up the altimeter Insert a battery to turn the altimeter ON The altitude of the previous flight will be reported If you hear a continuous tone instead the altimeter s built in self test is indicating a problem Do not attempt to launch if this condition exists After the previous flight altitude is reported the altimeter will be silent for 15 seconds while the electronics are stabilizing and ground level is being tracked The altimeter needs to be inserted into the rocket and the payload compartment sealed before this time elapses When the 15 second stabilization period ends the altimeter will indicate readiness with a short beep repeated every 1 5 seconds At this point the rocket is ready to launch Note If the payload compartment is not closed before the periodic beeping starts the altimeter should be removed turned OFF and then back ON and reinstalled If you close the payload compartment when the altimeter is in the periodic beep phase awaiting l
11. the diagram below and the mating data transfer adapter converts these to standard RS 232 serial levels Pin 1 Pin Function 1 N C 2 5V do not use 3 RX data 4 TX data 5 GND Figure 8 Serial I O connector and pinout Testing A simple apparatus for ground testing the altimeter can be made with a small jar and a length of plastic hose Drill a hole in the center of the jar s lid and insert one end of the plastic hose Glue hose in place to achieve a tight seal hot melt glue works well Turn on the altimeter and place it in the jar Tighten the lid and wait until you can hear the periodic beep from the altimeter indicating launch readiness Suck on the free end of the plastic hose to create a vacuum within the jar The altimeter will sense this as a launch condition and the beeping will stop When you stop sucking on the hose the altimeter will sense apogee as the pressure stabilizes Open the hose and allow air to bleed back into the jar and the altimeter will sense descent Approximately 5 seconds after the pressure has returned to normal the altimeter will beep out the altitude that your vacuum was able to create within the jar You may want to connect the computer interface and examine the flight profile that you created Note In order to eliminate false readings due to pressure transients at ejection and during Mach speed transitions the altimeter requires a smooth slow variation in pressure at apogee or t
12. the above terms by the purchaser and user 11
13. ude determination After a flight with the altimeter installed your rocket s peak altitude apogee will be reported via a series of audible beeps This will allow you to study the effect of various design parameters fin nose cone shape fin airfoil number of fins etc on your rocket s performance It can also be used by clubs for altitude contests compete to see who can get the most altitude out of a given engine size etc Y Download of flight data to a personal computer After recovery you can connect your altimeter to the serial port of an IBM compatible or Macintosh computer with the optional data transfer kit This allows you to view a graph of altitude vs time for the first 5 7 minutes of flight The data are also saved as a standard text file which can be imported into spreadsheet programs for further analysis velocity acceleration sink rate etc Theory of Operation The Alt15K WD altimeter determines altitude by sampling the surrounding air pressure during flight and comparing it with the air pressure at ground level As the altitude increases the air pressure decreases and the onboard microprocessor converts the pressure difference to altitude When the altimeter is turned on it checks the barometric pressure sensor to make sure that the pressure reading is within normal limits If an abnormal condition is detected an error is reported If pressure readings are normal the peak altitude of the previous flight is
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