TeleMetrum

This is a recording dual-deploy altimeter for high power model rocketry with integrated GPS and telemetry link.

Production units are available from the Garbee and Garbee web store.

These are photos of our current production version, which includes an integrated GPS receiver with active patch antenna:

Motivation

Bdale and Keith both own BeeLine trackers from Big Red Bee, and are pretty happy with them. They use a PIC processor and a TI CC1050 transmitter chip, and operate in the ham radio 70cm band.

One weekend while attending a conference together, we got to wondering if we couldn't adapt one to use as a downlink for the AltusMetrum altimeter board in addition to direction finding after flight. That caused us to start thinking about other things in the design we might want to tweak, and before long we were working on the design of a new tracker board derived from the BeeLine design. Another friend at the same conference showed us a board he was working on using a different part in the same TI series, that integrated a transceiver and CPU on the same chip. It didn't take us long to realize that with such a part we could combine and simplify things by building a new altimeter with integrated RF link! And after gaining some experience in 2009 with a first version, we realized we always want GPS on board, which lead to our current second generation boards.

Features

User View

• 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
• On-board, integrated GPS receiver
• On-board non-volatile memory for flight data storage
• USB for power, configuration, and data recovery
• Integrated support for LiPo rechargeable batteries
• Uses LiPo to fire e-matches, optional support for separate pyro battery
• 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube

Developer View

• Hardware Features
  • TI CC1111F32 Low Power RF System-on-Chip
    • Sub-1Ghz transceiver
    • 8051 MCU
    • 32k Flash
    • 4k RAM
    • USB 2.0
    • 6 12-bit analog inputs (11 bits with single-ended sensors)
    • 2 channels of serial I/O
    • digital I/O
  • Atmel AT45DB081D DataFlash memory
    • 1M x 8
    • 256 byte page size
    • SPI interface
    • other parts in this Atmel DataFlash series can optionally be used
  • SkyTraq Venus634FLPx GPS receiver
    • on-board Taoglas AP.17A.01 single-stage active patch antenna
    • U.FL connector with 3.3V DC can be re-purposed for optional external amplified antennas
    • async serial interface
  • Freescale MP3H6115A pressure sensor
  • Freescale MMA2202EG 50g accelerometer. Can use 40-200g variants!
• Software Features
  • Written mostly in C with some 8051 assembler
  • Runs from on-chip flash, uses on-chip RAM, stores flight data to serial DataFlash chip
  • USB serial emulation for "console" interface
• Tools Used
  • gEDA for schematic capture and PCB layout
  • SDCC compiler and source debugger
• Licenses
  • The hardware is licensed under the TAPR Open Hardware License
  • The software is licensed GPL version 2

Production History

Flight Logs

Artifacts

The user manual for TeleMetrum is available in html and pdf formats.

The hardware design current gEDA files are available from git.gag.com in the project hw/telemetrum.

Work on the next version proceeds on the master branch, with occasional temporary branches created when Bdale is making some major / speculative change. The 'v0.2' and 'v0.1' branches document what we're actually flying right now on the two respective PCB revisions. The 'ground' branch has a cut-down schematic used to generate the BOM for partially loading v0.1 boards to used on the ground. We call the on-the-ground version 'TeleDongle'.

For those who don't have ready access to the gEDA suite, here are pdf snapshots of the files for Production PCB version 1.0 in more easily readable form.

• schematic
• pcb artwork
• bill of materials

Our AltOS firmware works well enough that we now routinely fly TeleMetrum with no backup. Rockets with v0.1 boards have exceeded 50g acceleration, been above Mach 1, and reached altitudes greater than 12k feet AGL with great results. Keith's ground station program called ao-view logs telemetry to disk, displays current and max values for key parameters during flight, and even includes voice synthesis during the flight so that our eyes can stay on the rockets! We have post flight analysis software that makes it easy to extract data from the board, analyze it, and even generate KML files for viewing flights in GoogleEarth! More details on the software, including full source code and pre-built packages can be found on the AltOS page on this site.

Future Plans

As of May 2010, version v1.0 is available for sale from the Garbee and Garbee web store.

Because we understand that not everyone uses Linux, development of a new cross-platform ground station program written in Java is underway for use with AltOS.

Problems

• The CC1111F32 is a 36-pin QFN package, which necessitates reflow soldering. Since we needed to reflow solder anyway, and because TI used them in their reference design, we went a little crazy and used 0402 passive parts everywhere. That means working under a microscope to place parts! Without an inspection microscope, loading and testing these boards might be impossible.

• The addition of on-board GPS in v0.2 means that the total power consumption can exceed the rate at which we draw power from the USB interface, particularly when the GPS is in cold start mode. This means a battery must be attached during operation, and also that the battery will only charge effectively from USB when the board is turned off.

History

v0.2

These are photos of our second version, which included the integrated Venus GPS receiver, but with a passive patch antenna that turned out to have disappointing performance due to our many PCB geometry constraints. It also used a voltage regulator with less capacity which we felt was marginal for supporting the companion boards we have planned:

Other than cleaning up the silkscreen, the differences between v0.2 and our current v1.0 boards were really quite small:

• 100ma LDO regulator instead of the current 150ma part
• no C38 footprint
• different value for C36 reset capacitor

The schematics and PCB artwork for this version are on the v0.2 branch in our git repository, here are pdf copies for easy reference:

• schematic
• pcb artwork
• bill of materials

v0.1

And this is a photo of our original board with serial port for off-board GPS, without the big off-board 1000uF cap from the original ejection circuit:

The differences between v0.1 and later boards were substantial:

• 2.5 x 1 inch board with all parts mounted on one side
• 4-pin PicoBlade serial port connector for attachment of external GPS module
• USB connector projected approximately 3mm over the edge of the board
• Debug connector used 4 IC socket pins on 100 mil centers
• no companion board interface
• 50ma LDO regulator on early boards, later boards used a 100ma part
• Microchip 25LC1024 CMOS serial EEPROM instead of DataFlash
  • 128k x 8
  • SPI interface
• Microchip MCP9700A discrete temperature sensor
• used 1000uF electrolytic capacitor charged to 5V for pyro supply
• two LEDs instead of one attached to CPU

The elimination of the discrete temperature sensor and second LED were necessary to support the companion board interface added in v0.2.

The v0.1 artwork had three issues, two of which required physical rework on each board. All of these issues were fixed in v0.2.

• The USB connector footprint was placed wrong, so that the connector hung out over the edge of the board instead of being flush.
• We needed chip select on the SPI memory. To fix that, we gave up the ability to put the accelerometer into self-test mode and used that GPIO line to pull chip select on the memory, which required two cuts and two jumpers.
• The igniter sense circuits each needed a second resistor to complete the voltage divider so our 3.3V CPU ADC could read the 5V ejection voltage. This was fixed by changing two resistor values, and tacking two additional resistors onto the board with jumpers to ground.

The schematics and PCB artwork for this version as of the working-v0.1 tag are available here are pdf copies for easy reference:

• schematic
• pcb artwork
• bill of materials