Skip to main content

GAGA-1: Integration testing

And so it came to pass that I made the final solder joint to the GAGA-1 flight computer a little before midnight and was able to do an integration test of it and the recovery computer inside the capsule.

Here's the completed Arduino shield that has the GPS (top left), temperature sensors and radio transmitter (bottom middle) that makes up the flight computer. The gold SMA connector at the bottom right connects to the external antenna for telemetry transmission. The three pin connector above the transmitter connects to the external temperature sensor.

And here's a picture of the mounted flight and recovery computers ready for mounting inside the capsule.

And so I duly placed it in the GAGA-1 capsule and powered everything up and... it didn't work. Which was a bummer, but this is why I do these tests.

The following problems were discovered:

1. The DTR switch on the recovery computer is flaky. Sometimes it doesn't stick and hence the computer doesn't start running. In the event this happens on the day it's possible to connect to the computer and issue an AT#EXECSCR command to force start up.

2. The RTTY telemetry was garbled. This was a surprise and seems to be caused by the GPS module's interrupts. Added a new interface to disable and enable interrupts during RTTY send and the RTTY seemed stable.

3. The flight computer GPS was happily getting a lock and the packets containing the lock were being received correctly, but no fix was being recognized. This is because of the way I was handling translation of floating point numbers. The Lassen IQ sends a 4 byte IEEE 754 single precision number byte-by-byte to the Arduino which must then convert this to an Arduino float (which is exactly the same format). The cast I was using wasn't working and it's been replaced by a union:
union float32 {
  BYTE bytes[4];
  float value;
};  

#define COPY_SINGLE(_a,_b)            \
  {                                   \
      union float32 temp;             \
      temp.bytes[0] = packet[_b];     \
      temp.bytes[1] = packet[_b+1];   \
      temp.bytes[2] = packet[_b+2];   \
      temp.bytes[3] = packet[_b+3];   \
      last._a = temp.value;           \
  }
After that the recovery computer worked well and I received many SMS messages with the correct latitude and longitude of the middle of my back garden and an indication of the internal module temperature (around 15C).

The flight computer also worked, but it needs a second test before I'll be totally satisfied. I've yet to see a green bar on DL-FLDIGI indicating a successful decode of the GAGA-1 telemetry. This is essential for the tracker.

In other news the weather is still looking good for launch on Sunday. Here's the most recent prediction for 0900 UTC on April 10, 2011:

And GAGA-1 is getting a last minute addition. James Coxon asked if he could piggy back a Hellschreiber beacon on GAGA-1. So GAGA-1 will be flying with RTTY on 434.650 Mhz (the dial frequency I had last night was 434.652 Mhz) and Hellschreiber on 434.075 Mhz.

Comments

Popular posts from this blog

How to write a successful blog post

First, a quick clarification of 'successful'. In this instance, I mean a blog post that receives a large number of page views. For my, little blog the most successful post ever got almost 57,000 page views. Not a lot by some other standards, but I was pretty happy about it. Looking at the top 10 blog posts (by page views) on my site, I've tried to distill some wisdom about what made them successful. Your blog posting mileage may vary. 1. Avoid using the passive voice The Microsoft Word grammar checker has probably been telling you this for years, but the passive voice excludes the people involved in your blog post. And that includes you, the author, and the reader. By using personal pronouns like I, you and we, you will include the reader in your blog post. When I first started this blog I avoid using "I" because I thought I was being narcissistic. But we all like to read about other people, people help anchor a story in reality. Without people your bl

Your last name contains invalid characters

My last name is "Graham-Cumming". But here's a typical form response when I enter it: Does the web site have any idea how rude it is to claim that my last name contains invalid characters? Clearly not. What they actually meant is: our web site will not accept that hyphen in your last name. But do they say that? No, of course not. They decide to shove in my face the claim that there's something wrong with my name. There's nothing wrong with my name, just as there's nothing wrong with someone whose first name is Jean-Marie, or someone whose last name is O'Reilly. What is wrong is that way this is being handled. If the system can't cope with non-letters and spaces it needs to say that. How about the following error message: Our system is unable to process last names that contain non-letters, please replace them with spaces. Don't blame me for having a last name that your system doesn't like, whose fault is that? Saying "Your

The Elevator Button Problem

User interface design is hard. It's hard because people perceive apparently simple things very differently. For example, take a look at this interface to an elevator: From flickr Now imagine the following situation. You are on the third floor of this building and you wish to go to the tenth. The elevator is on the fifth floor and there's an indicator that tells you where it is. Which button do you press? Most people probably say: "press up" since they want to go up. Not long ago I watched someone do the opposite and questioned them about their behavior. They said: "well the elevator is on the fifth floor and I am on the third, so I want it to come down to me". Much can be learnt about the design of user interfaces by considering this, apparently, simple interface. If you think about the elevator button problem you'll find that something so simple has hidden depths. How do people learn about elevator calling? What's the right amount of