First Update in a Long Time

What has happened in that long time:
1) Fixed a bug with the camera and
2) Got connector for radio but have not actually hooked it up yet.

This may not seem like much, but I don't have much time now that school has started up again -- I am writing this while waiting for OpenOffice.org 3.3 to install so that I can go back to writing my lab report for ECE152B -- and it took a long time to get the parts from Marvac for reasons that I will tell after talking about the camera.  The bug with the camera was a major one that, like the earlier camera problems, was cause by bad documentation.  The bug made it so that the camera could only take one picture without being reset.  At first I did not notice this because I was only taking one picture per power cycle, which is obviously not an acceptable solution for the actual balloon.  Fortunately, once I realized that the problem existed, I was able to fix it after a couple of hours of browsing the manufactures forums.

Now for the radio connector story.  When I ordered the stuff for this project from digikey I was mainly focused on parts that would go on the PCB, and forgot that the radio needed a female connector.  Not wanting to pay the shipping from digikey to just get two connectors and the corresponding crimp on pins I decided to go to our local electronics store which, in retrospect, was a mistake.  When I walked into the store I asked if they had any connector housings with 20 pins in two rows with two mm square spacing.  The person helping me said yes.  Next I asked if they had any crimp on contacts that could go in the housing and the person said no, but he could order it for me. (OpenOffice 3.3 just finished installing, to be continued...)

Radio Update and Launch Site Considerations

I tried to get the connector for the radio module on Monday but Marvac didn't have it so they placed an order for it.  The order came in today but I didn't have time to pick it up before they closed because of school stuff, so I won't be able to get to work on that until tomorrow.  The interface to the radio seems simple, so it shouldn't take me to long to get it up and running.

We may and may not launch from the black rock desert.  I am now leaning towards a closer launch site, especially considering the large number of people that have expressed an interest in attending the launch.  For legal stuff on launching a balloon see FAA Title 14 Part 101(http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&rgn=div5&view=text&node=14:2.0.1.3.15&idno=14).  We have designed our balloon so that according to 101.1(Applicability) we only have to worry about the 101.7(Hazardous Operations).  As such we can legally launch pretty much anywhere that isn't populated.  That being said, very rugged terrain could make recovery difficult and our payload would likely be destroyed by a water landing, so we would favor a dry and flat area with little vegetation.  Prior to launch we will get an approximate landing position using the University of Wyoming's balloon trajectory forecast tool (http://weather.uwyo.edu/polar/balloon_traj.html) so that we can improve the likelihood of recovery and determine if it is a good time to launch.

GPS Integrated and Working

I didn't make any progress on our project the last couple days because I was at the Long Beach FIRST robotics regional with team 1717.  This morning I hooked up the GPS chip and got it working.  The latitude and longitude the GPS are outputting seem correct.  All that remains programming wise for the payload is to write the code for the radio transceiver.  Unfortunately, I can't start that today because I need to get a 20 pin connector and the local electronics store is closed on Sunday.  I'll go and get the connector between classes tomorrow and hopefully test the range of the radios next weekend.

Explanation of Electronics Design

Introduction
This post will only discuss the electronics on the balloon and not the tracking electronics on the ground.  The electronics payload consists of a printed circuit board(PCB), camera module, GPS module, radio module, and battery pack.  The above schematic is of the printed circuit board only.  As such, anything not on the PCB is not shown in it.  The PCB is responsible both for controlling the camera, GPS, and radio, and taking power from the battery pack and redistributing it to the other modules.

Battery Pack (not on PCB)
The battery pack we are using (http://www.sparkfun.com/products/550) holds 4 lithium ion AA batteries.  We chose to use lithium ion AAs because they are much less massive than alkaline batteries, they store more energy, are less affected by low temperatures, and don't cost that much more than alkaline batteries.  Each AA has a voltage of ~1.5V, so the output of the battery pack is ~6V.
Power Regulation
The power regulation electronics take the input voltage from the battery pack and step the voltage down to 5V and 3.3V for use by the other electronics.  I decided to run the output of the 5V regulator into the input of the 3.3V regulator because the 5V parts draw very little current relative to the 3.3V part.  The power dissipated by a linear voltage regulator is equal to the voltage drop across it times the current, so this daisy chaining reduces the power dissipated in the 3.3V regulator by about one third.  The increase in power dissipation in the 5V regulator is not a problem because the 5V parts draw such a small amount of current.
Controll Unit
What I have decided to call the "control unit" consists of  the Teensy 2.0 (a micro controller module), a microSD card adapter, a level shifter, and a mux/demux.  UART stands for universal asynchronous receiver transmitter, and is used by the Teensy to communicate with the camera, radio, and GPS.  The Teensy is a 5V part, but all of the other modules are 3.3V parts, so the output of the voltage of the Teensies UART port must be "shifted" down to the 3.3V range.  This is done by the SF LLC shown on the schematic.  Because the Teensy only has one UART port, a 74HC4052 is used to allow the single port communicate with more than one device.  A microSD card is used to store images from the camera as well as store a flight log consisting of all GPS coordinates received, all messages sent to the radio, all pictures taken by the camera, and any errors that occur.
Interface
The interface portion of the board has connectors on it to allow communication with the radio module, camera, and GPS.
Radio Module (not on PCB)
I chose to use a 1W COTS radio module, the  AC4790-1000, for communications.  I chose this module over building my own because although it would be cheaper to build my own, it would significantly increase debug and design times.

Casing

Hi fellows, my name is Kelly,

I design the casing and all mechanical parts.
It's not as hard as the electronics, but hey, someone has to do it.
Here are some drawings and pictures of the casing.

Here is the base board,
The idea is that basically everything goes on the base board and the parachute and balloon is connected directly to the base board. So even if the box breaks, all the electronics will still be protected by the base board and the parachute.















Here are the pictures of the wooden box.
We chose 1/4 inch wood board because it's anti-static, non conductive, light, cheap and easy to work with. I say it's a pretty ideal material where strength is not an issue.

Camera Working

After working pretty much from when I wake up until 2am the next day three days in a row, I've finally gotten the first good pictures off the camera (see above picture of my dog).  The color balance is still a bit off, but that can be fixed later.  The linksprite camera is a nice part the would be easy to use if it was well documented.  Unfortunately, the data sheet is laced with misspellings, errors, incomplete descriptions, and missing information.  After I complete this project I will make a document which correctly documents the communication protocol and includes sample code for getting data from the camera and post it to the SparkFun forums.

Background

Kelly and I have been working since summer on a balloon mission to near space.  I am now (finally) making a blog because of the large number of people that have been asking me if our project has one.  The goal of the project is to send a helium balloon to ~20km and take pictures and maintain communications with the ground throughout the flight.  I'll post more details about the electronics and software later, and Kelly will post more about the mechanical stuff.  Right now we are hoping to launch some time either over this break, or if there is not suitable weather, over a not busy weekend next quarter.  The above pictures are the first ones taken with the camera that will go on the balloon.  They were taken at 1/4 max resolution and there is clearly a problem with how we are reading the data from the camera, as can be seen in the weird stripes going across the image..