Contratulations to Bob Finch and Nathan Dalrymple for becoming our first customers to fly a rocket using a TeleMetrum board last Saturday! The rocket was Nathan's stretched BSD Horizon flying on a CTI Pro29 6xl 305-H226-14A Skidmark motor as shown in this launch photo.

I met both Bob and Nathan at the monthly club launch run by the Albuquerque Rocket Society at the same site in Rio Rancho, NM, earlier this year. That was the day I flew my first test flight with on-board GPS. They got excited about what they saw, and became two of our first customers for production boards.

Other than some rough edges with our first-generation ground software, Bob reported that everything worked as expected, and the GPS location received in the downlink got them to within about 10 feet of where the rocket set down.

In communicating their success to us on IRC, Bob said "MANY thanks to you guys, not only for the product but also for all the help getting me to the point of being able to use it !!". The pleasure is all ours, though, because after Bob asked us lots of new-user questions online, he wrote up his notes for us as "documentation for mere mortals" that will soon form the basis of a "getting started" section in our user manual.

Pretty cool stuff!

First, I was pleasantly surprised to discover that TeleMetrum is now the subject of a post on the Make magazine site. Very cool!

As reported last week, I've been waiting for better GPS antennas to arrive, but heavy snow here in Colorado last Friday delayed delivery. They finally arrived, and as I hoped, they appear to completely solve our signal strength problem!

So... [drum roll, please!]... I am very happy to announce that the first production build of TeleMetrum boards and starter kits are now "in stock" at the Garbee and Garbee web store, along with other products designed by the Altus Metrum community!

Keith and I are still working on the new Java-based ground station software and user documentation for the system. Watch this space for updates. I hope we'll have both ready for download by the time customers actually receive hardware...

Bdale has just opened up the Garbee and Garbee web store to sell Altus Metrum electronics including TeleMetrum and TeleDongle.

The TeleMetrum boards aren’t quite ready to ship, so they’re marked as ‘out of stock’ for another couple of days. That’s because we’ve decided to switch GPS antennas to improve GPS reception and we won’t have enough of those until Friday to start shipping boards. The TM boards themselves are working great and we’ve flown them several times.

We’ve already sold a couple of TeleDongle boards for use without TeleMetrum. These boards contain the CC1111 transceiver chip along with an 8-pin connector that can be used for USB, SPI or serial communication. This adds long-range wireless digital communication to almost any project. Steve Conklin has posted his plans for these boards. We sell TeleDongle as either bare boards or packaged in a pretty blue box with a USB cable attached.

All of the hardware designs are licensed under the TAPR open hardware license and software under the GPL. All of the tools used to design the hardware and build the software are also free software (already packaged for Debian, of course) so you can take these designs and do whatever you want with them.

I'm pleased to announce that the new Garbee and Garbee web store offering products designed by the Altus Metrum community is now open for business!

Rocketry folks, please note that I refuse to sell anything that isn't in stock, so if you want TeleMetrum boards you'll have to wait a few more days. Keith and I just weren't happy with the GPS receiver performance using the patch antennas we selected for version 1.0, and I'm changing to a slightly better (and more expensive) antenna that we expect will make everyone happier. Parts are due by Friday, and so with any luck you should be able to buy TeleMetrum boards and starter kits early next week.

In the meantime, we have TeleDongle boards and other accessories in stock now and ready to ship. Last week, Steve Conklin became our first customer by showing so much enthusiasm for TeleDongle over snacks at a conference we all attended for work that we pointed him to the web store under construction and he has already posted an enthusiastic blog entry about his plans!

More as it happens!

The first production run of TeleMetrum boards arrived from our assembler today, and overall things are looking good!

Unfortunately, I specified the wrong value for a capacitor associated with the new and improved 150mA 3.3 volt regulator. The resulting symptom was interesting to debug... everything seemed to be fine except that the GPS chip wouldn't talk to us. After some investigation, it became clear that the 3.3 volt power supply was taking much longer to stabilize than it should... long enough that the power-on reset circuit was relaxing before the supply was stable! The cc1111 apparently handles this just fine, but the GPS chip doesn't. Since the new cap is optional, just removing it caused everything on the first test board to start working! The ultimate solution will probably be to both replace the new bypass capacitor with one of the correct value, and to swap out the cap in the reset circuit for a somewhat larger value to ensure we have plenty of margin in the reset circuit.

I now have 4 of the new boards completed, turned on, and passing initial tests. Hopefully tomorrow I'll be able to wrap up the rest of the required functional testing. I then need to focus my attention on a business trip all of next week... but if all keeps going well, we're very close to taking our first orders.

Stay tuned!

I've been too busy (work, family, and fighting a nasty cold!) to write much text lately, other than the comments I put on launch photos uploaded to my Flickr stream, but the remainder of our testing of the prototype TeleMetrum v0.2 boards went really well!

The only significant change we decided to make before going to production was to change the 3.3 volt regulator from a 100mA to a 150mA part. This will ensure adequate power for the companion boards we have planned, even when the GPS chip is in maximum power mode searching for satellites during a cold start.

So... [drum roll, please]

Keith and I just placed the orders for our first production lot of TeleMetrum v1.0 boards! With any luck, in 3-4 weeks we should have a pile of altimeters to sell, along with the associated TeleDongle ground stations already in stock.

Stay tuned!

This afternoon, a box arrived from Advanced Circuits, containing 108 fully assembled TeleDongle boards!

This is not only the first "intended for sale" build of hardware from the Altus Metrum family of projects, it's also the first time that I've ever sent out one of my board designs for someone else to assemble. I therefore approached the turn-on and test of the first board out of the box with more than a little trepidation... fortunately, for no reason!

I'm immensely pleased to report that TeleDongle serial number 100 turned on and works entirely as expected!

I celebrated by packaging it in a cool little Hammond translucent blue plastic box with a USB cable, yielding the first prototype of a fully packaged TeleDongle board such as we anticipate selling for use receiving data from rockets carrying TeleMetrum boards.

We also intend to sell these boards as-is (flashed with default firmware and measured oscillator cal value) to folks who'd like a robust wireless link for their next microcontroller project, whether rocket-related or not. I will, of course, post something here when we're ready to start taking orders.

Now we just need the weather to cooperate long enough to log more test flights of TeleMetrum. The new version looks great so far, but I want a few more flights before I'll be confident enough to place an order with our assembler for a run of those too... Stay tuned!

On Saturday, I joined The Albuquerque Rocket Society monthly launch in Rio Rancho, NM. A friend, Mike, who lives in the area joined me for the launch. While the morning started off clear and calm, if a bit cold... the wind came up hard and we had to call it quits before lunch. But before the wind "blew us away", I managed to get one flight in. And it was an absolutely perfect test of one of my brand-new TeleMetrum v0.2 boards!

My cut-down Hawk Mountain "Raptor" kit, renamed "G-Spot" last October during my quest to exceed 50 g acceleration, was loaded with TeleMetrum serial number 51... and launched on a Cesaroni 229H255WT-14A motor.

The ascent was beautiful! I've put a few photos of the rocket leaving the launch rail up on flickr. However, despite a clear sky, we quickly lost sight of it! I managed to spot a bit of the smoke trail from the delay grain as the rocket approached apogee, but that was it! None of us at the launch saw anything after apogee!

After losing sight of the rocket, I turned my attention to my computer, where we were receiving a solid telemetry stream. It quickly became apparent that the rocket was descending normally under chute. As it got closer to the ground, I started calling out elevation, azimuth, and distance numbers, but still nobody could spot the rocket. As expected, we lost the RF link once the rocket reached the ground.

As various folks on the flight line wished me luck finding my rocket, I put the last reported GPS position into my hand-held receiver. Staring at the map display, Mike and I realized the rocket was far down range, near one of the roads into the site. We jumped into my vehicle and drove down the road to the point closest to the rocket's reported position. We then walked to where the GPS receiver said the rocket should be...

And found the rocket within about 20 feet! That was well within the window of position uncertainty my hand-held GPS was reporting at the time. Things just don't get much better than that! We picked up the rocket, and returned to the flight line only a few minutes after leaving it. After dumping the data from the board's on-board memory, I quickly generated the usual plots, along with a kml file that can be viewed in Google Earth.

The rocket reached 1881 meters apogee, or around 6173 feet, and the maximum acceleration was 19.5 g. It touched down nearly 1.3 miles down range from the launch rail, in sage-brush desert. I honestly don't think I would have found the rocket without at least the radio beacon. It was hugely gratifying that the GPS worked and let me walk right up to the rocket! I could not have asked for a better test of the new electronics!

Later in the day, Keith flew a successful test of serial number 52 at a launch in Wilsonville, Oregon.

We're very happy with these results! Weather permitting, I hope to get more test flights in next weekend at Hudson Ranch. Stay tuned!

Test Flying TeleMetrum v0.2

Bdale and I got a chance to test fly the new version (0.2) of our TeleMetrum flight computers. Bdale flew with the Albuquerque Rocket Society down in New Mexico while I flew near home with Oregon Rocketry during our February model launch.

I flew my Dynastar Grappler which I have modified to create a large payload bay out of a foot of the original body tube:

I cut a sled out of plywood and mounted the TeleMetrum on one side, and a small 110mAh battery on the back:

The field we use for model launches is surrounded by tall fir trees, so we tend to stick to reasonably small motors. This time, I loaded up an Aerotech 24mm E18 motor and trimmed the delay down to about 5 seconds as this rocket uses simple motor ejection. This flight didn’t exercise the new ejection circuitry. In any case, the flight was perfect, telemetry worked all the way down to the ground using just a 1/4 wave whip antenna on the receiver.

Here’s the data recorded in the on-board eeprom:

The maximum reported altitude was 186m, velocity was 49m/s and acceleration was 53m/s².

As expected, the GPS loses tracking during boost, but rapidly re-acquires near apogee and tracks the rocket all the way back to the ground. The flight track can be viewed in Google Earth.

Needless to say, both Bdale and I are extremely pleased with the performance of the new hardware.

Introducing TeleMetrum v0.2

Bdale and I (mostly Bdale, of course) finished the TeleMetrum v0.2 design work in December, and this weekend we got boards made and parts ordered and Bdale sat down with his trusty electric skillet and built 3 new boards. The new design has an integrated GPS receiver and patch antenna, and is otherwise fairly similar in design to v0.1.

TeleMetrum v0.2 Hardware

Here’s the front side of the board:

From the left, you’ll see a connector for an external power switch and the two ejection charge circuits, a battery connector for a single 3.7V lipo cell, the GPS patch antenna, a 4-pin debug connector, the piezo buzzer and the new 8-pin companion board connector. We weren’t happy with the connectors used on the v0.1 board and finally found these Tyco Micro-MaTch parts which take up a modest amount of board space (more than pico-blade connectors, less than regular pin blocks), have a locking option and crimp on to standard ribbon cable. They’re also bright red and surprisingly low in profile.

And here’s the back side:

Elements on this side include the new 100μF cap in the upper left corner which sits on the 3.3V supply to try and keep the CPU alive through minor power glitches. Below that is a new package containing a pair of FETs for the ejection circuits. We used discrete FETs in v0.1, but this device has better specs for our needs (lower on resistance, etc). The USB connector was pulled in-board far enough to keep it from hanging over the edge. Right of that is the new data logging chip, and right of that is a U.FL connector in case you want to use an external GPS antenna. We supply power to that connector as most external GPS antennas include their own LNA. And, of course, to the right of that is the Skytraq Venus 634 GPS receiver.

Below and to the right of the GPS receiver is the cc1111, to the left lies the accelerometer and then the barometric pressure sensor above the 5V boost regulator which powers the accelerometer. We haven’t found any high-G accelerometers that run on 3.3V yet. Finally the two tiny 5-pin chips are the USB LiPo charger and the 3.3V regulator. What you can’t see easily are a pile of 0402 passive components scattered across the board. Even close up, they’re hard to pick out by eye.

The only hardware ‘bug’ was in the reset logic — the new board was designed with a much larger capacitor on the reset line than the old board. The debug code would only hold the reset line low for a brief instant, sufficient for the old capacitor value but not the new one. Instead of fixing the code, Bdale decided to try a smaller capacitor value and found that it worked just fine. After that, the board came up just fine and the updated firmware was flashed into the CPU.

TeleMetrum v0.2 Software

The only significant software change was that the data logging part changed from a 25LC1024 1Mbit eeprom to an AT45DB161D 16Mbit DataFlash. This required writing a new driver, but fortunately much of the code could be copied from the 25LC1024 driver. Because the AT45DB161D comes from a family of similar-but-different parts ranging from 1Mbit to 64Mbits, I decided to make the code automatically adapt to the installed part, detecting which one was attached and adjusting the driver.

The story here is that the configuration data didn’t appear to be getting preserved across reboots — we use the last block of the data logging part to hold configuration data, including call sign, sensor calibration values and flight parameters. A bit of testing and we found that the code to read/write the device worked perfectly. It turns out that a premature optimization in detecting which kind of flash part was installed had a race condition when multiple threads were trying to access storage at the same time, resulting in the configuration data being left uninitialized. Oops!

The TeleMetrum firmware has a clever hack for selecting between ground mode (for fetching data from the device or altering the configuration) and flight mode (prepared to fly the rocket). It switches between these by detecting whether the board is upright (flight mode) or not (idle mode). However, the accelerometer must be calibrated to tell the difference. What never occurred to us was that if the calibration data was broken enough, the device might always come up in flight mode. In that mode, it isn’t listing to either USB or the radio link, so it’s impossible to fix the accelerometer calibration data.

A bit of brainstorming led to a fairly simple hack — check to see if one of the pins on the companion connector was shorted to ground at power on time, if so, force the computer to enter idle mode. Pin 1 of the companion connector is ground, and fortunately, pin 2 was the SPI clock pin, normally output-only, so we could safely use that in this mode as any companion device shouldn’t ever pull that low.

Future Events

As of this evening, three boards are built and mostly tested; the radios appear to work, GPS tracks satellites and the beeper makes plenty of noise. Still to check is whether the deployment circuits will fire an ematch (we’ve tested the design before, just not this specific implementation).

Next weekend, we’re off to linux.conf.au in Wellington, New Zealand where we’re scheduled to give a presentation on the hardware and software in TeleMetrum. We’ll have v0.2 boards to show off, so come and see them in person.

With v0.1, we used the same board design for both flight computer and ground station, TeleDongle. For TeleDongle, we just left most of the components off of the board and loaded alternate firmware. For v0.2, we’re planning on building a separate TeleDongle board; that design is finished but no boards are made yet.

Once we’re happy with the design, we’ve got big plans to get more boards made so we can let a few friends buy them for use them in their own rocket projects. That should happen in the next month or so. Once we’ve gotten enough testing done, and made sure that other people can actually operate them without hand-holding from us, we’ll make them available for sale to the general rocket-flying public.

Beyond that, we’ve got plans to build more stuff:

1. A stand-alone ground station, called TeleTerra, that would include an LCD readout and flight data recording so you wouldn’t need a laptop during the flight.

2. A companion board, called TelePyro, to control 8 additional pyro channels. These could be used for almost anything from air starts to staging or any other whacky plans.