Adept Rocketry - ALTS20 Instructions and Data Sheet

ALTS20 Maximum Altitude Altimeter with Dual Deployment™

Copyright © 1999-2005, All Rights Reserved


The ALTS20 Altimeter with Dual Deployment™ is a maximum altitude altimeter that measures and reports the maximum above-ground altitude value obtained during a rocket’s flight. The ALTS20 also has two altitude controlled deployment switches that are typically used to fire deployment charges, based on altitude. The first charge fires when the rocket reaches its maximum altitude (apogee), and the second charge fires when the rocket descends to 1,200 or 600 or 300 feet above ground (user selectable). One common usage is to deploy a main parachute at apogee by using only the first output. However, the most typical usage is to deploy a drogue chute or streamer first, then to deploy a main parachute when the rocket descends to 1,200 or 600 or 300 feet, in order to avoid significant drifting due to wind.

This device is used in rockets that will reach at least 300 feet altitude. Either or both deployment switches may be used, or the device may be used as a maximum altitude altimeter only. The ALTS20 may be used in any rocket configuration including multistage rockets, in which case maximum altitude information about a particular stage can be obtained by placing the device in the particular stage of interest. Or individual ALTS20 units (or other altimeter devices) may be placed in each stage of interest to report maximum altitudes obtained by each stage, and/or to handle deployment for each stage.

The ALTS20 captures the highest altitude obtained during a flight to a maximum of 25,000 feet above sea level (by special order the ALTS20 can be calibrated to altitudes up to 60,000 feet). The maximum value obtained above the local ground-zero altitude is reported in one-foot increments. For instance, the altitude in Denver, Colorado is about 5,000 feet. The ALTS20 would accurately report the maximum altitude obtained above ground level to a maximum of 20,000 feet, (five digits). The altitude is reported in one-foot increments with an accuracy of 5% of the reading for any flight. But for several flights of the altimeter from the same location, the readings can compare to each other as closely as 1%. This information can be quite handy when studying a series of flights of the same vehicle. The flights should be done from the same location, and at the same barometric pressure and temperature for most accurate comparison results.

The ALTS20 measures 1” wide by .75” thick by 4.45” long. It fits inside a tube with a minimum ID of 26 mm, or slightly more than one inch. The device weighs only 1 ounce, including the battery. It uses a 12-volt alkaline lighter battery, and when only the maximum altitude function is being used, the battery life is in excess of 12 hours, so you need not be concerned about how long your rocket sits on the launchpad after the unit is powered up. The battery life, when the deployment switches are being used is about two hours, still enough time for several flights. Note: the two hours is only a judgement call; it is only our suggestion in order to assure that the battery voltage is still plenty high enough for the large capacitor to have more than enough energy to fire a flashbulb or low-current electric match charge. The ALTS20 is a totally stand-alone device including the battery holder, the arming mechanism, and the current source for firing deployment charges. Nothing more is required except for the wires (interconnect cable) that connect to the On-Off switch and to the deployment charges.

The altimeter uses an absolute pressure device to measure altitude values up to 25,000 (or 60,000) feet in one-foot increments. It uses a logarithmic amplifier to accurately measure the nonlinear pressure versus altitude relationship over this large altitude range. Once powered up, the ALTS20 reports that neither, or one or both deployment charges has continuity. It also constantly measures the ground-level altitude and waits for a quick 300-foot change upward. It then captures the maximum altitude obtained above ground zero. The first deployment switch fires at the very moment when the rocket reaches the maximum altitude. The second switch fires when the descending altitude reaches either 1,200 or 600 or 300 feet above the ground, as preset by the user. The ALTS20 uses the copyrighted and patented technique of beeping out (blinking on some models) a value to report the maximum altitude value. The beeps can be heard even when the unit is still inside the rocket. The rocketeer knows the maximum altitude as soon as he/she picks it up, or just gets close to it. Note: the ALTS20 cannot be used for, and will not function for, maximum altitudes less than 300 feet.


  • Altitude Capability: to 25,000 feet above sea level (up to 60,000 feet above sea level by special order).
  • Lowest Maximum Altitude Readable: 300 feet above ground. Liftoff is detected when the altitude quickly increases by 300 feet.
  • Accuracy Over Full Range: +/- 5% of reading with all barometric, temperature, and other conditions considered. Calibration accuracy is +/- 1%, typical.
  • Uses 12-volt lighter battery and has large integral capacitor to fire flashbulb or electric match charges. Battery Life: 8 hours to minimum working voltage for maximum altitude function only. Suggested battery usage when using deployment switch outputs is up to 2 hours.
  • Piezo beeper reports altitude and operational status including the continuity of the deployment devices. One repeating beep if neither device has continuity, two beeps repeating if only device #1 has continuity, three beeps if only device #2 has continuity, and four beeps if both devices have continuity.
  • Switch #1 fires when the altitude reaches maximum; Switch #2 fires during descent at 1,200 or 600 or 300 feet as selected by the user, or 1 second after Switch #1, whichever occurs last.
  • Measures 1” wide by .75” thick by 4.45” long and fits inside a tube with a minimum ID of 26 mm, or slightly over one inch. It may be mounted to plates or bulkheads in larger diameters. Avoid mounting it vertically with the battery holder spring toward the bottom.
  • Weighs only 1 ounce with battery installed.

Accessories Required: one 12-volt alkaline lighter battery, and one cable (Adept CAB6L-xx series) to connect an On-Off switch and deployment charges.


NOTE 1: The precision amplifier circuitry and continuity sensing circuitry on the ALTS20 may be sensitive to noise and static when being held. A 10-second silent time following power up gives time to get your hands off the unit before it starts taking readings. Always handle the device by the edges when testing or installing to avoid touching any of the circuitry. Avoid carpeted floors and other sources of static electricity when handling and testing the device. Never store the device in a clear plastic bag; however, pink-colored or smoke-colored antistatic bags are ideal. Storage in a small cardboard box, or wrapped in a paper towel inside a plastic bag is acceptable. Do not use Velcro to secure the device. Use care to keep the device clean and dry.

NOTE 2: This device must be installed only in a “clean area.” Electronic Instrumentation is not compatible with the fumes and residue created by rocket motors and deployment charges. The ALTS20 must be installed in an area that is totally sealed from motors and charges. After passing wires through holes in bulkheads and such, seal them with epoxy or removable putty.

Install a 12-volt alkaline lighter battery (GP-23A, Eveready Energizer No. A23, Radio Shack 23-144, etc.) in the battery holder. The spring end of the battery holder connects to the negative end of the battery. Remove the battery when not in use to avoid prolonged stress on the battery holder and possible long-term disfigurement.

Connect an Adept CAB6L-xx series interconnect cable to the 6-pin connector on the ALTS20.

The BLACK and BROWN wires enable power to the altimeter when they are connected together. They may be connected to an On-Off switch.

The RED and ORANGE wires connect to the first deployment charge, the one that fires at apogee.

The YELLOW and GREEN wires connect to the second deployment charge, the one that fires during descent at 1,200 or 600 or 300 feet (preset by user).

To turn the unit on, connect the BLACK wire and the BROWN wire together. Typically these wires will connect to a normally-open On-Off switch or other device. Or the two wires simply may be twisted together. The unit sounds out a long pulsating beep when powered up, to indicate proper operation. After ten seconds of silence the unit starts beeping once a second to indicate that it is now taking altitude readings and is waiting for liftoff.

If flashbulbs or low-current electric matches are connected (don’t connect anything quite yet), the beeping changes from a single beep to other beeping patterns to indicate continuity of the deployment charges. A single beep indicates proper operation with no deployment charges connected. A double beep indicates continuity of only the first output or first deployment charge, the one that fires at apogee (maximum altitude). A triple beep indicates continuity of only the second output or second deployment charge, the one that fires during descent at 1,200 or 600 or 300 feet. Four beeps repeating indicates that both deployment charges have continuity.


When viewing the front of the ALTS20 (with the cable connector at the top, and the battery holder near the bottom), a 3-pin connector J1 is located at the lower left corner of the battery holder. When no jumper is installed on the connector, the default altitude setting is 600 feet. The second deployment charge will fire during descent at 600 feet. When a shorting jumper (Radio Shack Cat. No. 276-1512 or equivalent) is installed on the lower two pins, the setting is 300 feet, the lower value setting. When the jumper is installed on the upper two pins, the setting is 1,200 feet.

To simulate rocket liftoff it is necessary to pull a vacuum on the top of the pressure sensor (the black gizmo with four pins). A quarter-inch diameter piece of plastic or rubber tubing can be used. You need only hold the vacuum for a few seconds, then release slowly. However, the best method is to put the whole device (including wires and flashbulbs for testing the output switches) inside a small wide-mouth juice bottle, and pull a vacuum on the bottle. It is easy to simulate rocket flights to altitudes of several thousand feet. Slowly pull the vacuum, then slowly release the vacuum. As the vacuum (altitude) increases, the ALTS20 will BOOP to indicate that 300 feet has been reached (liftoff). Then when the altitude starts its descent (vacuum is being released), a BEEP will indicate that the maximum altitude was reached, and this is when the first output (apogee) flashbulb fires. When the simulated altitude falls to 1,200 or 600 or 300 feet above the original ground level, there will be a long BEEP, and this is when the second output flashbulb fires. The unit then begins reporting the maximum altitude.

After a flight, the altimeter will be beeping out the maximum altitude in this manner: (1,321 feet) Beep .....Beep Beep Beep.....Beep Beep.....Beep. A zero is indicated with a lower tone BOOP: (1,302 feet) Beep.....Beep Beep Beep.....BOOP.....Beep Beep. After each sequence there is a long pause before it repeats. The system works for three, four, or five digits depending on the value. This system is copyrighted and patented.

Warning: never install this device in a rocket without first testing its controlling outputs. Always test before each flight. Also, backup deployment systems and/or instrument redundancy (use of two similar systems in the same rocket) are highly recommended.


The ALTS20 may be installed lengthwise in a small-diameter rocket tube. It will fit lengthwise in a tube with an ID of just over an inch, a loose fit in a 29 mm tube. It may be mounted to plates or bulkheads inside larger diameter tubes. The mounting holes are .090 inch diameter for #2 hardware. Use #2 screws, standoffs, and hexnuts when mounting the altimeter to a plate or bulkhead. Do not enlarge the mounting holes, and do not use Velcro.

An altimeter must be installed in a “sealed” chamber with a vent or vents to the outside. A sealed bulkhead below the altimeter chamber is necessary to avoid the vacuum caused by the aft end of a rocket during flight. A sealed bulkhead above the altimeter chamber is necessary to avoid any pressure fluctuations that may be created at the nose end of the rocket.

The vent (also known as a static port) to the outside of the rocket must be in an area where there are no obstacles above it that can cause turbulent air flow over the vent hole. Do not allow screws, ornamental objects, or anything that protrudes out from the rocket body to be in line with and forward of a vent hole. The vent must be neat and burr free and on an outside surface that is smooth and vertical where airflow is smooth without turbulence.

Some rocketeers use multiple static ports (vent holes) instead of just one. Very strong wind blowing directly on a single static port could affect the altimeter. Multiple ports evenly spaced around the rocket tube may help cancel the effects of strong wind, the pressure effects of a non-stable liftoff, or the pressure effects that occur due to flipping and spinning after deployment. If you wish to use multiple ports, then use three or four. Never use two. Ports must be the same size and evenly spaced in line around the tube.

The general guideline for choosing port size is to use one 1/4 inch diameter vent hole (or equivalent area, if multiple holes are used) per 100 cubic inches of volume in the altimeter chamber. For instance, An eight-inch long four-inch diameter tube has a volume of about 100 cubic inches. Use one 1/4 inch port, or four 1/8 inch ports evenly spaced around the tube. An altimeter chamber two inches in diameter and eight inches long (25 cubic inches) needs one 1/8 inch vent hole or four 1/16 inch vent holes. Try to keep hole sizes within -50% or +100% of the general guideline.

Vent holes should be a minimum of four body diameters below the junction of the nosecone with the rocket body. This is necessary with high performance (high speed) rockets. The tremendous pressure on the nosecone leeches down the rocket body as much as four diameters before it dissipates.


Adept Rocketry and Adept Instruments, Inc. warrant to the original purchaser that this product is free of defective parts and workmanship and that it will remain in good working order for a period of 90 days from the date of original purchase. This product will be repaired or replaced within 90 days of purchase if it fails to operate as specified, if returned by the original purchaser and if it has not been damaged or modified, or serviced by anyone other than the manufacturer. Adept Rocketry and Adept Instruments, Inc., their owners, employees, vendors and contractors shall not be liable for any special, incidental, or consequential damages or for loss, damage or expense directly or indirectly arising from customer’s or anyone’s use of or inability to use this device either separately or in combination with other equipment, or for personal injury or loss or destruction of other property, for experiment failure, or for any other cause. This device is sold as an experimental accessory only, and due to the nature of experimental carriers such as rockets, the possibility of failure can never be totally removed. It is up to the user, the experimenter, to use good judgement and safe design practices and to properly pretest the device for its intended performance in the intended vehicle, or reasonable facsimile of same, under controlled conditions to gain reasonable belief that the device and vehicle will perform in a safe manner, and to assure that all reasonable precautions are exercised to prevent injury or damage to anyone or anything.

WARNING: Do not use this device unless you completely understand, agree with, and accept all the above statements and conditions., 11-18-05