Iridium Flare Tracker

A 2004 BurningMan project

for the Alternative Energy Zone village

(Yes, this is one of those quickly assembled "done in notepad" type of sites, nothing fancy. This page is designed as a central repository for all the flaretracker information that I've been putting in my LJ the last few weeks. Most of the cool photos are on page 2.)

(NOTE: The project has been renamed "C.L.I.V.E" and a new intro page added.)

Jump to: History | Components | Description | Behavior | Laser safety | Intro | Progress (page #2) | Ideas and changes (page #3) | Aftermath (page #4)



The Fools Doing This:


Back around 1998 or so I read about how the communications satellites for Iridium had a main mission antenna that would reflect the sun directly back at earth as the satellite crossed the terminator, causing a 'flare' that was excessively bright. Using info from the Heavens Above website I got into the habit of watching these flares from the balcony of my office before going home in the evening (yay for late-evening network gigs). I found it fascinating just how visible satellites can be and how rarely people notice them. Most humans just don't look up unless distracted properly into doing so, I guess. That year at Burning Man I was mulling through art-project ideas with my friend Cary. Between us we came up with the thought of building a tracker of some kind with a big mechanical arm to point at the next flare's location; something we could leave out on the playa for people to watch. Like many on-playa 'for next year!' ideas, Not much was done with it.

Zoom forwards to earlier this year. Slashdot posted a short article about the xport 2.0, a Xilinx-FPGA based development system that uses a Nintendo GameBoy Advance as its host controller. This news rapidly motivates Garth, my code-addicted roomate. Within minutes he's got one ordered and headed his way in the mail. He has no idea what to do with it, of course. This was the usual tech-geek case of having an excellent new hammer and really badly needing a nail to use it on.

The memory of the old Iridium Flare Tracker idea came up and it got Garth's gears grinding. The first stunt that Garth made the xport do was to slap on a few basic 7-segment LED displays from Radio Shack and a 7448 BCD-to-7-segment decoder IC. Voila! instant counter. (Or funky characters like the picture shows). This first step got us fired up to actually give it a go. A few napkins-and-scribbles sessions at various eateries around the South Bay area later and we had a basic idea of what we wanted to do. A nail had been found. :)

Please keep in mind as you read this that the two of us only have the most basic of digital-logic-circuitry skills. All I ever had was an electronics class in High School; Garth had a little more but not much. He's got the programming skills; I've got the Hakko 703 station and way too much practice using it. The rest we had to pick up along the way, using the UberTool.

And now, on to the project itself.


Device Description:

Yes, I'm aware these are just crappy napkin-sketches. Deal. :) (Update: I've added pictures of real devices the sketches turned into)

First is the controller itself. The Xport has two "user outputs". These are hooked into each of the signal distribution boards using a standard 34-pin floppy cable. The first port controlls the countdown clock. The second port controlls the laser turntable, the GPS and all other I/O. (Update 7/13: Next to the full system sketch is a picture of the partially assembled case containing the GBA/Xport and main distribution boards. Next to that is the system set up with two test digits during one of our outdoor tests.)

The countdown clock is the easy part. The distribution board has the cable from the xport (a 34-pin ribbon cable) on one side alongside a daisy-chain port. The other has seven cat-5 jacks and a 12v DC input port. Each clock is made of seven digits (HH:MM:SS.s) connected to the seven ports. Each digit has its own sub-controller board with a 7448 BCD-to-7-segment chip and switching transistors. These control seven segments of 6 LEDs each to make the 2'-high numbers at a rather harsh brightness. They also have a PWM pin so we can modulate the brightness from the controller. (Update 7/6: We're now putting two digits and a colon per 'digit board', so three boards can make up one side of the clock instead of 6. We've also made the last digit "Magnitude" instead of tenths of a second, to be mounted separately)
(Update 7/10: Pictured is one of our 1/4" plastic sheet "test digits", front and back, with wire-wrap LEDs. The real digits will be done on 1/4" plywood with LED lenses)

Digit and Digit Controller Boards

You can run multiple clocks off this configuration. Simply daisy-chain the distribution boards and feed each one its own 12vDC supply (max draw, about 2.5a if all digit segments are lit at 100% duty cycle). Right now we're only planning on two: a front-and-back so the clock can be seen on either side of the installation. The clock will be aligned so it's viewable from the center of the playa. I don't know how many we could stack until we ran out of control signal; we're only building two anyway.

Main Distribution Board

The other distribution board sends off to a stepper-motor-controller board. That board is hooked to a turntable that holds the laser head and a Futaba servo with a mirror mounted on it, giving a 360deg rotation (with anti-wrap for the laser driver cable) and 10-80 degree elevation range for the laser. flares occur between 11deg and 70 degrees of the horizon. We want to mount the turntable above head-height and never aim the laser below 10 degrees for participant eye-safety. Another pin off the same board will provide PWM to the laser's power supply so we can strobe the beam as needed. (Update 7/6: The laser-control board now controls the stepper motors, servo and PWM for the laser. It will connect to the distribution board with a Cat5 cable.)

Laser Control Board

That same distribution board will go to an I/O card that plugs into the GPS reciever. The receiver provides us accurate timing for the countdown. For now the flare-tracker operates off of a pre-defined table of events -- but in the future we'd like to use the position info to be able to compute the flare locations on its own, wherever it gets plunked down. It'll still need updated orbital information but that's kind of unavoidable. (Update 7/6: The serial port was put directly on the distribution board instead of offloaded to its own circuitry. We've also added another Cat5 jack for a remote keyboard.)

Secondary Distribution Board

The remainder of the IO pins on the secondary card are reserved for future expansion. We may add things like a daylight-viewable pointer (aimable robotic arm of some kind) for pointing at the rare daylight flares that happen. The xport has way too many I/O pins... but we'll find a use for them all. :) (Update 7/6: We have 10 general purpose IO pins plus ground and +3.3V available. They're now on the main distribution board hooked up to a pinblock for easy connection to external alarm circuits, etc.)

The whole assembly hooks into a tiny little GameBoy advance. The buttons on the GBA and its screen will be used to do setup and change parameters on the operating device. Everything tucks away into a dust-filtered box to keep it alive out on the Playa and the whole unit will be powered by a bank of 12v lead-acid batteries. These will be charged by Unisolar-64 panels through a Trace charge controller, making the whole thing sun-powered and self-sustaining. We're still working out the exact power budget for the device but it currently looks like this will be no problem, even with leaving the laser to run all night for the whole week. This part is easy because we've built it for prior BurningMan events.

Our solar array from BM2001

Device Behavior:

At the start of the week we set it up. One sealed box (with dust-filters to allow for airflow) will contain all the electronics. Two large poles or boards will be mounted on secure stands (go go gadget Rebar) and used to hold the clock's frame. The cables for the clock run up one pole from the electronics box. The rotation table/laser system will then be stuck up on top of one side, the GPS on the other. (Update: 7/15: Added a Version 2 sketch to show how we're changing the system to look)

Version 1

Version 2

Actual construction

The laser itself will be inside of a circular baffle, like a hatbox. This way the laser can never shine lower than 10 degrees angle. All people will see is the green beam exiting the top (and maybe an EL band wrapped around the outside for looks). The cable sticks out through a hole and has enough slack to be allowed to rotate 270 degrees each way from center (safety distance past the 180deg it will need. The code has setup for anti-wrap and safety cutoff to avoid cable-yanking).

On the installation pole we'll put a plaque explaining what the device does and what Iridium flares are all about. At night this plaque will be lit by white LEDs.

Out comes the ladder and we calibrate the table/mirror array for true north and level and run tests to make sure of our aiming accuracy. We then take the latest-greatest table of flare predictions (downloaded the day before arriving at the desert) and put them into the system. The GPS gets the proper time and the system starts.

During the day, the clock counts down at full brightness, indicating the time of the next flare. At night the clock dims to a 'don't blind the natives' level and the laser turns on, pointing at the sky. When it's 10 minutes before an event, the laser blinks and the clock plays digit-games as an attractor to anybody watching. During the last minute the laser blinks faster and faster until it starts to dim. The clock will flash all-zeros (also dimmed so not to overpower the satellite's light) and the laser will give single, bright pulses once a second for about .1s each. This should keep folks focussed on the right spot of the sky while the actual iridium flare takes over the show for 10-20 seconds.

Once the flare has passed the clock will reset animatedly. The laser will swing to its new position, draw a figure-eight around the target point, and then settle. The clock starts counting down once more.

Repeat until the end of the festival.

Currently the GPS is only used for highly accurate time. All the iridium flares will be pre-listed in a table supplied by the wonderful folks at Heavens Above. Future versions of this tracker (or heck, this version if we have enough time) could use the positioning information to compute the flares on their own. The system would still require a current set of orbit prediction tables but those are global in nature, allowing the device to then work wherever you plunked it down.

Other ideas are still forming for the extra signal pins. Maybe some gumball-flashers as a warning before the last minute... or an audible tone. There's more to think about here. We also need to find a few interested artist-friends to help us decorate up the tech to make it look more ornate. I'm already thinking about doing some of my own add-ons as an excuse to re-learn artistic welding. I'm thinking a nice classic-astronomy look with various ringed planets and astrolabe-looking fiddly bits will be nice.

Laser Safety Note:

We've had a few people (mostly private pilots) email us about laser safety vs. aircraft. Someone even helpfully sent us a copy of the FAA regulations about such things. I just wanted to pass on that we're adhering to those guidelines and are well below the power limits for our proximity to controlled flight zones in our area. Please keep in mind that we're at a maximum of 0.085 watts; often we run lower than that when doing testing. The beam images you see on these pages are 10 to 20 second exposures. As much as we'd hope for such a thing, this is no Green Beam of Death. :)

Most all of our testing is indoors. The few we do outside we're very good to watch the power and to be aware of any aircraft overhead. Please don't think we're poorly thought out enough to go outside and wave a 5-watt beam around like a toy lightsaber. Many of our friends are both private and professional pilots and we know the risks all too well. We're being respectful and careful about it.

As far as safety at the event itself, we're going to be keeping the beam platform above head-height and (as mentioned earlier) never able to go below 10 degrees elevation. There should be no real chance of someone getting a direct hit from the beam. Our biggest worry would be if someone plowed into the entire installation in a runaway art-car and sent it flying into bits.

From here you can
Go to page 2 to see our progress, page 3 to see changes and new ideas that have come up, page 4 to see CLIVE at BurningMan or return to the intro.

Contacts: Tor Amundson and Garth Minette . Questions, suggestions and criticisms appreciated! Flames will most likely be snickered at.

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This work is licensed under a Creative Commons License.