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I'm pleased to announce that, at long last, the ChaosKey hardware random number generator described in talks at Debconf 14 in Portland and Debconf 16 in Cape Town is now available for purchase from Garbee and Garbee.

Posted Wed Aug 3 15:17:55 2016 Tags:

I woke up this morning and realized that for the first time since 17 April 2001, I am no longer a member of the Debian Technical Committee.

My departure from the committee is a consequence of the Debian General Resolution "limiting the term of the technical committee members" that was passed amending the Debian Constitution nearly a year ago. As the two longest-serving members, both over the term limit, Steve Langasek and I completed our service yesterday.

In early March 2015, I stepped down from the role of chairman after serving in that role for the better part of a decade, to help ensure a smooth transition. Don Armstrong is now serving admirably in that role, I have the utmost respect for the remaining members of the TC, and the process of nominating replacements for the two now-vacant seats is already well underway.

So, for the Debian project as a whole, today is really a non-event... which is exactly as it should be! Debian has been a part of my life since 1994, and I sincerely hope to be able to remain involved for many years to come!

Posted Fri Jan 1 11:39:25 2016 Tags:

Keith and I are pleased to announce the immediate availability of EasyMega v1.0!

EasyMega is effectively a TeleMega without the GPS receiver and radio telemetry system. TeleMega and EasyMega both have 6 pyro channels and enough sensors to lock out pyro events based on conditions like tilt-angle from vertical, making both boards ideal solutions for complex projects with air start or multi-stage engine ignition requirements. Choose TeleMega for a complete in-airframe solution including radio telemetry and GPS, or EasyMega if you already have a tracking solution you like and just need intelligent control of multiple pyro events.

EasyMega is 2.25 x 1.25 inches (57.15 x 31.75 mm), which means it can be easily mounted in a 38 mm air frame coupler. The list price for EasyMega is $300, but as an introductory special, you can purchase one now through Labor Day for only $250! This special is only good for in-person purchases at Airfest and orders placed directly through Bdale's web store.

Altus Metrum products are available directly from Bdale's web store, and from these distributors:

All Altus Metrum products are completely open hardware and open source. The hardware design details and all source code are openly available for download, and advanced users are invited to join our developer community and help to enhance and extend the system. You can learn more about Altus Metrum products at http://altusmetrum.org.

Posted Thu Aug 28 21:12:51 2014 Tags:

A year ago today, on 11 June 2013, daughter Elizabeth and I smelled smoke, kicking off an adrenalin-pumped afternoon evacuating our home, which was located very close to the point of origin of the Black Forest Fire. The short version is that we ended up losing our house and most of our "stuff", but all the people, pets, and a few of our most prized possessions escaped unscathed. If you need more details, I told a longer version of the story at Linux Conf Australia in Perth this January.

This has been an experience I would not wish on my worst enemy... but a year later, I'm pleased to report that life is largely back to normal and things are moving along just fine! The 2-bedroom apartment we found to live in while rebuilding has been sufficient to our needs, but we can't wait to move in to the new house under construction on our property in a couple more months. And after graduating from Oberlin College with a degree in physics and minor in the classics, we're very pleased that Elizabeth is back with us for a while this summer before she starts the next phase of her life as a research assistant and PhD candidate at the ASU Center for Science and the Imagination in August. And Altus Metrum, LLC is successfully back in business producing some cool new toys...

We owe an immense debt of gratitude to you, our many friends both near and far, who have shown us so much caring and support in the last year. Thank you!

Posted Wed Jun 11 09:09:09 2014 Tags:

Keith and I are pleased to announce the immediate availability of TeleGPS v1.0!

TeleGPS is our response to the many requests we've received for an easy-to-use tracking-only board that just provides GPS position information over radio. Combining the same uBlox Max 7Q GPS receiver used in TeleMega and TeleMetrum v2.0 with a 16mW transmitter yields a board that is 1.5 x 1.0 inches (38.1 x 25.4 mm).

As usual for our products, TeleGPS is designed for use under FCC Part 97 (ham radio) rules or equivalent authorization. In addition to the GPS receiver and UHF radio transmitter, TeleGPS includes on-board flash data storage and a micro USB connector for configuration, post-flight data download, and to power a LiPo battery charger.

TeleGPS works with our existing ground station products and/or any radio equipped with APRS support, and also emits audible radio direction finding beeps. While TeleGPS can be used with our existing AltosUI and AltosDroid ground station software, Keith is working on a simpler, dedicated application optimized for use with TeleGPS.

Altus Metrum products are available directly from Bdale's web store, and from these distributors:

All Altus Metrum products are completely open hardware and open source. The hardware design details and all source code are openly available for download, and advanced users are invited to join our developer community and help to enhance and extend the system. You can learn more about Altus Metrum products at http://altusmetrum.org.

Thank you all for your continuing support of Altus Metrum, and we hope to see you on a flight line somewhere soon!

Posted Sun Jun 8 18:53:15 2014 Tags:

Keith and I are pleased to announce the immediate availability of TeleMetrum v2.0, the return of TeleDongle, and that TeleMega is back in stock!

We've taken our classic TeleMetrum design and updated it with all new components. Same feature set, but better in every way. TeleMetrum v2 is a dual deploy flight computer with 2 pyro channels, 105g accelerometer, 100k' barometer, uBlox Max 7Q GPS and >30mW telemetry system with APRS support.

Read more about TeleMetrum v2.

Our original ground station TeleDongle is also back at last, as a part of the Altus Metrum Starter Pack. Each Starter Pack includes a TeleDongle USB-connected ground station for laptops running Linux, Mac OS X or Windows, a battery compatible with any Altus Metrum flight computer, a USB cable, and an Altus Metrum cut vinyl decal.

Read more about TeleDongle

We're also pleased to have TeleMega back in stock! TeleMega is an advanced flight computer with 9-axis IMU, 6 pyro channels, uBlox Max 7Q GPS and >30mW telemetry system with APRS support. We designed TeleMega to be the ideal flight computer for sustainers and other complex projects

Read more about TeleMega

Altus Metrum products are available directly from Bdale's web store, and from these distributors:

All Altus Metrum products are completely open hardware and open source. The hardware design details and all source code are openly available for download, and advanced users are invited to join our developer community and help to enhance and extend the system. You can learn more about Altus Metrum products at http://altusmetrum.org.

Thank you all for your continuing support of Altus Metrum, and we hope to see you on a flight line somewhere soon!

Posted Fri Feb 14 11:46:53 2014 Tags:

Yay! One of my talk proposals was accepted. Looking forward to LCA in Perth in January...

Posted Wed Sep 4 08:15:13 2013 Tags:

Keith and I are pleased to announce the immediate availability of TeleBT, a new Altus Metrum ground station product providing the equivalent of TeleDongle plus Bluetooth.

TeleBT working with AltosDroid on an Android device provides everything needed to monitor a rocket in flight, record telemetry, and know how to walk right to the airframe after it's back on the ground.

The Bluetooth capability of TeleBT is also supported by AltosUI on Linux, and with a micro USB cable TeleBT works just like TeleDongle on Windows, Mac, and Linux systems running AltOS version 1.2.1 or later.

Posted Tue May 21 13:55:18 2013 Tags:

In my post about Batteries and Pyro Circuits, one of my suggestions was to remove the protection circuit board from LiPo cells used with Altus Metrum flight computers. To help out folks who want to do this themselves, I put together and posted a how-to with photos in the Documents section of our web site.

Posted Mon Apr 29 11:00:12 2013 Tags:

Keith and I have discovered a change in the behavior of the protection circuits integrated in the LiPo batteries we sell for use with Altus Metrum products that poses a risk for our customers. This post is meant to document what we now know, communicate changes we're planning as a result, and explain what we think flyers of our existing electronics and batteries may want to do to maximize their chances of successful flights.


Choosing batteries and designing pyro circuits for high power rocketry avionics involves a variety of trade-offs. Reliability is the highest concern, both because nobody wants to lose an airframe due to a failed pyro event, and also because airframes recovering anomalously have safety implications. But we also care about other factors including cost and weight, and usually want to minimize the complexity of both the electronics and the overall installation.

The objective of a pyro circuit is to dump enough energy rapidly into an electric match to cause it to catch fire. We need batteries both to power the electronics that decide when to fire the charge, and to provide the energy that actually ignites the match.

The two most common battery types seen in the rocketry hobby are alkaline cells, often the nominal 9V rectangular variety, and rechargeable batteries based on Lithium Polymer (LiPo) chemistry. LiPo cells are 3.7 volts per cell nominal voltage, are very light, and have a high energy density.

LiPo capacity is measured in units of current times time, so an 850mAh cell should be able to deliver 850 milliamps for an hour. The battery industry also uses something called a "C rate" to describe how fast the battery can be usefully discharged, wich is a multiplier relative to the battery capacity. So a battery with 850mAh capacity and a "2C" rating can deliver current at a sustained rate of 1700mA until discharged, while the same capacity at a "5C" rating can deliver 4250mA.

By comparison, most 9V alkaline batteries are actually composed of 6 individual 1.5V cells enclosed in a wrapper. It's hard to get hard numbers for capacity and discharge rate, since in an alkaline cell the two are not independent, and the discharge rate is related to the volume of each individual cell. The data sheet for an Energizer 522 shows just over 600mAh at a 25mA discharge rate, dropping to about 300mAh at a 500mA discharge rate.

Importantly for use in pyro circuits, LiPo cells have a very low source impedance, which means they can source immense amounts of current. It's not unusual for cells in the 1000mAh range to have ratings in excess of 30C! Because this rapid discharge ability can pose a risk of fire, it's common for LiPo cells to come with a "protection board" integrated into the battery assembly that is designed to limit the current to some rate such as 2C continuous duty.

In large airframes, or projects that involve staging, air-starts, or other complex pyro event sequences, the most reliable approach will always be to use separate batteries for the control electronics and the source of pyro firing power. In the limit, having separate pyro batteries for each pyro charge with the control electronics only providing the switching to connect the batteries to the charges could even make sense. But for most airframes, this is overkill, and the increases in mass, volume, and wiring complexity just don't make sense.

The challenge, then, is how to design electronics that will robustly initiate pyro events without negatively affecting the rest of the electronics when operating from a single shared battery.

Altus Metrum Pyro Circuits

The very first prototypes of TeleMetrum were designed to use a single-cell LiPo battery, and had an on-board 100mA charging circuit. Because we needed 5 volts to power the accelerometer, we had a small switching regulator that up-converted the LiPo voltage, and we used some of that regulator's output to charge a 1000uF capacitor. The pyro circuit used Fairchild FDN335N N-channel MOSFET switches in a low-side switching configuration to dump the energy stored in the capacitor through an attached ematch. Those FETs had an on resistance of under a tenth of an ohm in our operating conditions. The circuit worked very reliably, but the 1000uF electrolytic cap was huge and we struggled with the mechanics of such a large part hanging off the board...

It turns out that 3.7 volts is way more than enough to fire a typical low-current e-match or equivalents like the Quest Q2G2 igniters. In fact, bench testing with a good digital oscilloscope showed that a typical e-match with resistance of 1.3-1.8 ohms will fire in approximately 13 microseconds when hit with the nominal 3.7 volts from a LiPo.

So, starting with our v0.2 boards, we switched to using the LiPo battery voltage directly to fire the pyro charges, eliminating the clunky electrolytic capacitor entirely. We also switched to the Fairchild FDS9926A dual N-channel MOSFET whose specs are better in all regards for our application. The on resistance is down around 40 milli-ohms in our circuit, such that the current ratings are much higher (FET current limits are primarily driven by how much heat is generated due to current flowing through the channel's on resistance).

Because using the LiPo voltage directly means we're effectively temporarily putting a very low resistance across the battery during the pyro events, the input voltage to the voltage regulator gets pulled down. To ensure the processor could "ride through" these events, we added a 100uF surface mount bulk capacitor on the 3.3 volt regulated voltage rail, which bench testing demonstrated was more than sufficient to maintain processor operation through pyro events. And that is essentially the same pyro circuit on all the boards, both TeleMetrum and TeleMini, that we have shipped to date.

What's Changed

The LiPo batteries we source and sell with our electronics come with a protection board and cable terminated in a 2-pin, 2mm "JST" connector. The specs on the protection board have always been "2C continuous", but we observed the ability to source much higher currents for short periods such as the 13 micro-seconds or so required to fire an e-match. Thus these protection circuits seemed just fine .. we could fire e-matches with a burst of current but were protected against short circuits in the wiring or our boards by the 2C continuous limit.

Unfortunately, the most recent batch of batteries we sourced seem to have a much "twitchier" protection circuit. We can draw more than 2C for short bursts, but not as much as with prior boards, and not for as long an interval. With a 1 ohm power resistor on the pyro terminals of one of our boards, we get about 9 milliseconds of power before the protection circuit cuts in and shuts the battery down. The power stays down until all load is removed, which at least means the board is turned off and back on again, and in some cases could even mean the battery is unplugged and re-plugged since we draw trace current to keep the GPS memory alive even when the power is turned off, and at least some of the new batteries see that as enough to keep the power turned off after an over-current event.

For many e-matches, this isn't an issue, since 9 milliseconds is way longer than the 13 microseconds needed to fire the charge. Unfortunately, we've discovered that many of the e-matches bought and used in the rocketry hobby are actually made for use in the fireworks industry, where it is desireable to retain continuity after firing so that series connections of e-matches all can fire even if some fire faster than others! This means that while the resistance goes up some after firing, sometimes the drain on the battery remains sufficient to cause the protection circuit to kick in even after the pyro charge has fired.

What We're Doing About It

If we remove the protection circuit from the LiPo (or jumper around it), all existing Altus Metrum products will operate successfully with pyro charges thave have an effective resistance of as low as 1 ohm. That's lower than any e-match or Q2G2 we've ever seen, so in effect what this means is that if you have an existing Altus Metrum flight computer, and you remove the LiPo protection circuit, you're good to go. This does not really make things any more "dangerous", since our battery chargers are all current limited and our discharge patterns will never cause heating of the battery. Frankly, in a rocket, the most likely way to cause a problem with a LiPo is by smashing or puncturing the actual battery during bench work or during a crash... and those cause the same problems with or without a protection board present.

In the future, we will ship batteries that have either a much higher C rating on the protection circuit, or have no protection circuit at all.

The number of problems reported by actual customers that we think should be attributed to LiPo protection circuit boards is very low, and we suspect most of our customers who are happily flying their boards can continue to do so. Ground testing where you fire pyro charges (or at least e-matches) using RF to issue the commands (not USB, since the LiPo charger is running any time USB is connected!) will confirm whether there's a problem. If the board resets (does startup beeps) after a pyro event, or shuts down completely (no LED activity), then you have a problem. If the matches light and the board keeps running, you're good to go.

However, any Altus Metrum customer with LiPo batteries sourced from us or our distributors who is worried about this problem (even if you haven't seen problems in ground testing or previous flights), and who doesn't want to try soldering on the battery circuit board yourself, is welcome to contact us about removing the protection circuit for you. We won't charge anything other than shipping.

To take advantage of this offer, just send email to fixmybattery@altusmetrum.org telling us how many of which capacity batteries you have that you'd like updated, and we'll respond with an RMA number and shipping details.

Going Even Further

As previously indicated, with the LiPo protection circuits removed, all of our current products will work reliably with at least 1 ohm across the pyro terminals. That should cover all real-world flying conditions just fine, but we're not satisfied yet.

We've designed a new pyro control circuit that transfers the maximum possible energy to the load regardless of battery voltage without ever allowing the voltage to the processor to droop at all. We're testing this new circuit in various prototypes now, and if it pans out it will probably show up first in MegaMetrum and then trickle down to TeleMetrum and TeleMini as those products are updated later this year. The new pyro circuit tolerates 0 ohms (dead shorts) on the pyro terminals for as long as the battery can provide current, which is as good as it gets. We think the circuit is clever enough that we'll probably write more about it once we're finished validating it.

Posted Wed Apr 10 21:25:02 2013 Tags: