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Showing posts from January, 2012

Using GNU Make's 'define' and '$(eval)' to automate rule creation

About once a week I get an email from someone random asking a question about GNU Make. I do my best to answer and figured it might be helpful for others if I shared these questions and my answers. So, here goes. This one starts with a Princess Leia style appeal:
I stumbled across your name when googling for help on a GNUmake related problem, hope you have the time to look at it as you are my last hope. I have the following problem in my Makefile:
$(LIBDIR)/libfoo.a: $(filter $(OBJDIR)/foo/%,$(OBJECTS)) $(LIBDIR)/libbar.a: $(filter $(OBJDIR)/bar/%,$(OBJECTS)) $(LIBDIR)/libbaz.a: $(filter $(OBJDIR)/baz/%,$(OBJECTS)) $(LIBDIR)/%.a: ar -r [email protected] $^ ranlib [email protected] so far, so good - it works as expected. The only problem is, that in the real world it's not just foo, bar and baz for me and I hate having to maintain the list manually. What I would like to do is something like this:
$(LIBDIR)/lib%.a: $(filter $(OBJDIR)/%/%,$(OBJECTS)) ar -r [email protected] $^ ranlib [email protected] but now …

GAGA-2: Mounting the flight computer

On GAGA-1 the flight computer was screwed in place using nylon bolts that went through the polystyrene walls of the capsule. GAGA-2 is using cable ties.

One concern with cable ties is their performance at low temperature. The CUSF guys had warned me never to use cable ties for load bearing joints. But since we are holding in place a few grams of flight computer the only remaining concern was whether the cable ties would still be locked at low temperature.

So, I locked together a pair of ties and left them in the freezer at -18C overnight.

The next morning they showed no signs of slippage and I was unable to pull them apart. But for double safety I've also superglued the locking part of the cable ties shut in place.

Here's the flight computer inside the capsule:

There are a pair of cable ties around the two board of the flight computer (the Arduino and the custom shield on top containing the radio transmitter and the GPS). Those help keep them together.

Then there are a pa…

GAGA-2: Distance RTTY Test

As I said in my previous post about GAGA-2 one vital test was the the radio transmitter worked over a long distance. I'd done the same test for GAGA-1 and went back to the same location for a GAGA-2 test.

My father drove off to one end of the reservoir with GAGA-2 transmitting happily from the back of his car (an estate car) and I drove to the other with my radio and a Yagi. It was obvious as I was driving to the listening point across the reservoir that things were going to work because I could still hear GAGA-2 from time to time using a simple whip aerial.

Once on the causeway in the left of the picture I hopped out of the car and pointed the Yagi in roughly the right direction. The RTTY signal came in loud and clear. Moving the Yagi from side to side made it easy to figure out where the transmitter was.

Measuring on Google Maps shows that this time the distance was roughly 6km (3.7 miles) with trees and the body of the car in the way (GAGA-2 wasn't even lifted up to wind…

GAGA-2

Last April I sent a weather balloon up into the stratosphere after months of preparation. You can read all the details starting here. I called the flight GAGA-1. Well, it's time for a GAGA-2.

Since last April I've done a number of experiments with expanding foam to see if it would make a viable material for the GAGA-2 capsule. Summary: no. It's too hard to work with, it doesn't insulate that well and I can get a cheap polystyrene capsule that's much smaller than the GAGA-1 capsule.

So, GAGA-2 will aim for a spring time 2012 flight with a number of changes from GAGA-1. First, a much smaller, lighter capsule. Second, video cameras rather than still. Third, no backup GSM based tracker.

Here's the new capsule. It's made from a pair of hollow polystyrene spheres that fit one inside the other.

These are very, very light. Weighing in at a total of 68g (compare that to GAGA-1's capsule that weighed more than 200g).

The inner sphere is covered in the sam…

International Object Sizing Tool

I often take pictures of objects for this blog when I'm making stuff (such as the Cansole or Home-made 7x7 display) and one constant problem is scale. It's hard for people to know what size the objects are. For example, here's a small HD video camera that I'm planning to use on GAGA-2. This shot shows the camera with its insides out:

Tiny, but how small?

To solve the problem I've created the International Object Sizing Tool that can be photographed alongside an object to give an idea of scale. It has five different ways of showing the size of the object: three common coins, a credit card and centimeter and inch scales. Here it is:

The entire thing is credit card sized (itself an international standard) and I've included the Visa logo and a fake card number and name so that you can recognize it as a credit card sized object.

There's an inches scale on the left, a centimeters scale on the top and three correctly scaled coins: a one Euro, a US quarter and a…