Bdale Garbee Keith Packard 2010 Bdale Garbee and Keith Packard Owner's Manual for the TeleMetrum System This document is released under the terms of the Creative Commons ShareAlike 3.0 license. 0.1 30 March 2010 Initial content Welcome to the Altus Metrum community! Our circuits and software reflect our passion for both hobby rocketry and Free Software. We hope their capabilities and performance will delight you in every way, but by releasing all of our hardware and software designs under open licenses, we also hope to empower you to take as active a role in our collective future as you wish! The focal point of our community is TeleMetrum, a dual deploy altimeter with fully integrated GPS and radio telemetry as standard features, and a "companion interface" that will support optional capabilities in the future. Complementing TeleMetrum is TeleDongle, a USB to RF interface for communicating with TeleMetrum. Combined with your choice of antenna and notebook computer, TeleDongle and our associated user interface software form a complete ground station capable of logging and displaying in-flight telemetry, aiding rocket recovery, then processing and archiving flight data for analysis and review. Recording altimeter for model rocketry. Supports dual deployment (can fire 2 ejection charges). 70cm ham-band transceiver for telemetry downlink. Barometric pressure sensor good to 45k feet MSL. 1-axis high-g accelerometer for motor characterization, capable of +/- 50g using default part. On-board, integrated GPS receiver with 5hz update rate capability. On-board 1 megabyte non-volatile memory for flight data storage. USB interface for battery charging, configuration, and data recovery. Fully integrated support for LiPo rechargeable batteries. Uses LiPo to fire e-matches, support for optional separate pyro battery if needed. 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube. TeleMetrum is a sophisticated electronic device. When handled gently and properly installed in an airframe, it will deliver extraordinary results. However, like all electronic devices, there are some precautions you must take. The Lithium Polymer rechargeable batteries used with TeleMetrum have an extraordinary power density. This is great because we can fly with much less battery mass than if we used alkaline batteries or previous generation rechargeable batteries... but if they are punctured or their leads are allowed to short, they can and will release their energy very rapidly! Thus we recommend that you take some care when handling our batteries and consider giving them some extra protection in your airframe. We often wrap them in suitable scraps of closed-cell packing foam before strapping them down, for example. The TeleMetrum barometric sensor is sensitive to sunlight. In normal mounting situations, it and all of the other surface mount components are "down" towards whatever the underlying mounting surface is, so this is not normally a problem. Please consider this, though, when designing an installation, for example, in a 29mm airframe's see-through plastic payload bay. The TeleMetrum barometric sensor sampling port must be able to "breathe", both by not being covered by foam or tape or other materials that might directly block the hole on the top of the sensor, but also by having a suitable static vent to outside air. As with all other rocketry electronics, TeleMetrum must be protected from exposure to corrosive motor exhaust and ejection charge gasses. TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to fit inside coupler for 29mm airframe tubing, but using it in a tube that small in diameter may require some creativity in mounting and wiring to succeed! The default 1/4 wave UHF wire antenna attached to the center of the nose-cone end of the board is about 7 inches long, and wiring for a power switch and the e-matches for apogee and main ejection charges depart from the fin can end of the board. Given all this, an ideal "simple" avionics bay for TeleMetrum should have at least 10 inches of interior length. A typical TeleMetrum installation using the on-board GPS antenna and default wire UHF antenna involves attaching only a suitable Lithium Polymer battery, a single pole switch for power on/off, and two pairs of wires connecting e-matches for the apogee and main ejection charges. By default, we use the unregulated output of the LiPo battery directly to fire ejection charges. This works marvelously with standard e-matches from companies like [insert company and product names for e-matches we've tried and like] and with Quest Q2G2 igniters. However, if you want or need to use a separate pyro battery, you can do so by adding a second 2mm connector to position B2 on the board and cutting the thick pcb trace connecting the LiPo battery to the pyro circuit between the two silk screen marks on the surface mount side of the board shown here [insert photo] We offer two choices of pyro and power switch connector, or you can choose neither and solder wires directly to the board. All three choices are reasonable depending on the constraints of your airframe. Our favorite option when there is sufficient room above the board is to use the Tyco pin header with polarization and locking. If you choose this option, you crimp individual wires for the power switch and e-matches into a mating connector, and installing and removing the TeleMetrum board from an airframe is as easy as plugging or unplugging two connectors. If the airframe will not support this much height or if you want to be able to directly attach e-match leads to the board, we offer a screw terminal block. This is very similar to what most other altimeter vendors provide by default and so may be the most familiar option. You'll need a very small straight blade screwdriver to connect and disconnect the board in this case, such as you might find in a jeweler's screwdriver set. Finally, you can forego both options and solder wires directly to the board, which may be the best choice for minimum diameter and/or minimum mass designs. For most airframes, the integrated GPS antenna and wire UHF antenna are a great combination. However, if you are installing in a carbon-fiber electronics bay which is opaque to RF signals, you may need to use off-board external antennas instead. In this case, you can order TeleMetrum with an SMA connector for the UHF antenna connection, and you can unplug the integrated GPS antenna and select an appropriate off-board GPS antenna with cable terminating in a U.FL connector.

The AltOS firmware build for TeleMetrum has two fundamental modes, "idle" and "flight". Which of these modes the firmware operates in is determined by the orientation of the rocket (well, actually the board, of course...) at the time power is switched on. If the rocket is "nose up", then TeleMetrum assumes it's on a rail or rod being prepared for launch, so the firmware chooses flight mode. However, if the rocket is more or less horizontal, the firmware instead enters idle mode. In flight mode, TeleMetrum turns on the GPS system, engages the flight state machine, goes into transmit-only mode on the RF link sending telemetry, and waits for launch to be detected. Flight mode is indicated by an audible "di-dah-dah-dit" on the beeper, followed by beeps indicating the state of the pyrotechnic igniter continuity. One beep indicates [FIXME] apogee continuity, two beeps indicate main continuity, three beeps indicate both apogee and main continuity, and one longer "brap" sound indicates no continuity. For a dual deploy flight, make sure you're getting three beeps before launching! For apogee-only or motor eject flights, do what makes sense. In idle mode, the normal flight state machine is disengaged, and thus no ejection charges will fire. TeleMetrum also listens on the RF link when in idle mode for packet mode requests sent from TeleDongle. Commands can thus be issues to a TeleMetrum in idle mode over either USB or the RF link equivalently. Idle mode is useful for configuring TeleMetrum, for extracting data from the on-board storage chip after flight, and for ground testing pyro charges. One "neat trick" of particular value when TeleMetrum is used with very large airframes, is that you can power the board up while the rocket is horizontal, such that it comes up in idle mode. Then you can raise the airframe to launch position, use a TeleDongle to open a packet connection, and issue a 'reset' command which will cause TeleMetrum to reboot, realize it's now nose-up, and thus choose flight mode. This is much safer than standing on the top step of a rickety step-ladder or hanging off the side of a launch tower with a screw-driver trying to turn on your avionics before installing igniters!

TeleMetrum includes a complete GPS receiver. See a later section for a brief explanation of how GPS works that will help you understand the information in the telemetry stream. The bottom line is that the TeleMetrum GPS receiver needs to lock onto at least four satellites to obtain a solid 3 dimensional position fix and know what time it is! TeleMetrum provides backup power to the GPS chip any time a LiPo battery is connected. This allows the receiver to "warm start" on the launch rail much faster than if every power-on were a "cold start" for the GPS receiver. In typical operations, powering up TeleMetrum on the flight line in idle mode while performing final airframe preparation will be sufficient to allow the GPS receiver to cold start and acquire lock. Then the board can be powered down during RSO review and installation on a launch rod or rail. When the board is turned back on, the GPS system should lock very quickly, typically long before igniter installation and return to the flight line are complete.

An important aspect of preparing a rocket using electronic deployment for flight is ground testing the recovery system. Thanks to the bi-directional RF link central to the Altus Metrum system, this can be accomplished in a TeleMetrum-equipped rocket without as much work as you may be accustomed to with other systems. It can even be fun! Just prep the rocket for flight, then power up TeleMetrum while the airframe is horizontal. This will cause the firmware to go into "idle" mode, in which the normal flight state machine is disabled and charges will not fire without manual command. Then, establish an RF packet connection from a TeleDongle-equipped computer using the P command from a safe distance. You can now command TeleMetrum to fire the apogee or main charges to complete your testing.

The chip our boards are based on incorporates an RF transceiver, but it's not a full duplex system... each end can only be transmitting or receiving at any given moment. So we have to decide how to manage the link... By design, TeleMetrum firmware listens for an RF connection when it's in "idle mode" (turned on while the rocket is horizontal), which allows us to use the RF link to configure the rocket, do things like ejection tests, and extract data after a flight without having to crack open the airframe. However, when the board is in "flight mode" (turned on when the rocket is vertical) the TeleMetrum only transmits and doesn't listen at all. That's because we want to put ultimate priority on event detection and getting telemetry out of the rocket and out over the RF link in case the rocket crashes and we aren't able to extract data later... We don't use a 'normal packet radio' mode because they're just too inefficient. GFSK is just FSK with the baseband pulses passed through a Gaussian filter before they go into the modulator to limit the transmitted bandwidth. When combined with the hardware forward error correction support in the cc1111 chip, this allows us to have a very robust 38.4 kilobit data link with only 10 milliwatts of transmit power, a whip antenna in the rocket, and a hand-held Yagi on the ground. We've had a test flight above 12k AGL with good reception, and my calculations say we should be good to 40k AGL or more with just a 5-element yagi on the ground. I expect to push 30k with a 54mm minimum airframe I'm working on now, so we'll hopefully have further practical confirmation of our link margin in a few months. Placeholder.

First off, in the US, you need an [amateur radio license](../Radio) or other authorization to legally operate the radio transmitters that are part of our products.

In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours. By default, we ship TeleMetrum with a simple wire antenna. If your electronics bay or the airframe it resides within is made of carbon fiber, which is opaque to RF signals, you may choose to have an SMA connector installed so that you can run a coaxial cable to an antenna mounted elsewhere in the rocket.

To receive the data stream from the rocket, you need an antenna and short feedline connected to one of our [TeleDongle](../TeleDongle) units. The TeleDongle in turn plugs directly into the USB port on a notebook computer. Because TeleDongle looks like a simple serial port, your computer does not require special device drivers... just plug it in. Right now, all of our application software is written for Linux. However, because we understand that many people run Windows or MacOS, we are working on a new ground station program written in Java that should work on all operating systems. After the flight, you can use the RF link to extract the more detailed data logged in the rocket, or you can use a mini USB cable to plug into the TeleMetrum board directly. Pulling out the data without having to open up the rocket is pretty cool! A USB cable is also how you charge the LiPo battery, so you'll want one of those anyway... the same cable used by lots of digital cameras and other modern electronic stuff will work fine. If your rocket lands out of sight, you may enjoy having a hand-held GPS receiver, so that you can put in a waypoint for the last reported rocket position before touch-down. This makes looking for your rocket a lot like Geo-Cacheing... just go to the waypoint and look around starting from there. You may also enjoy having a ham radio "HT" that covers the 70cm band... you can use that with your antenna to direction-find the rocket on the ground the same way you can use a Walston or Beeline tracker. This can be handy if the rocket is hiding in sage brush or a tree, or if the last GPS position doesn't get you close enough because the rocket dropped into a canyon, or the wind is blowing it across a dry lake bed, or something like that... Keith and Bdale both currently own and use the Yaesu VX-7R at launches. So, to recap, on the ground the hardware you'll need includes: an antenna and feedline a TeleDongle a notebook computer optionally, a handheld GPS receiver optionally, an HT or receiver covering 435 Mhz The best hand-held commercial directional antennas we've found for radio direction finding rockets are from Arrow Antennas. The 440-3 and 440-5 are both good choices for finding a TeleMetrum-equipped rocket when used with a suitable 70cm HT.

Our software makes it easy to log the data from each flight, both the telemetry received over the RF link during the flight itself, and the more complete data log recorded in the DataFlash memory on the TeleMetrum board. Once this data is on your computer, our postflight tools make it easy to quickly get to the numbers everyone wants, like apogee altitude, max acceleration, and max velocity. You can also generate and view a standard set of plots showing the altitude, acceleration, and velocity of the rocket during flight. And you can even export a data file useable with Google Maps and Google Earth for visualizing the flight path in two or three dimensions! Our ultimate goal is to emit a set of files for each flight that can be published as a web page per flight, or just viewed on your local disk with a web browser.

In the future, we intend to offer "companion boards" for the rocket that will plug in to TeleMetrum to collect additional data, provide more pyro channels, and so forth. A reference design for a companion board will be documented soon, and will be compatible with open source Arduino programming tools. We are also working on the design of a hand-held ground terminal that will allow monitoring the rocket's status, collecting data during flight, and logging data after flight without the need for a notebook computer on the flight line. Particularly since it is so difficult to read most notebook screens in direct sunlight, we think this will be a great thing to have. Because all of our work is open, both the hardware designs and the software, if you have some great idea for an addition to the current Altus Metrum family, feel free to dive in and help! Or let us know what you'd like to see that we aren't already working on, and maybe we'll get excited about it too...

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