When I was a kid, I was always eager for Sunday morning, just waiting for the time to watch Carl Sagan’s “Cosmos” on TV.
Back then, my couch turned into a spacecraft and I could go to places light-years distant from home. All was discovery and astonishment.
One thing that got me mostly surprised was to know that the Earth had multiple atmospheric layers, and contrary to the common sense, there are upper layers that are hotter than lower ones. This always caught my imagination, and I have been fascinated by this kind of subject ever since.
After many years, I got to know a hobby that put me in direct contact with this childhood passion: High Altitude Balloonism, a.k.a. HAB. It is a hobby where people send unmanned aircraft into the stratosphere to take pictures and videos, to gather scientific data, having a pretty good time in preparing for the missions.
It is an opportunity to learn a lot while we have tons of fun.
One of the skills most needed in HAB is electronics: to design and build the flight instruments, the data logging modules, and to integrate with radio communication, cameras and GPS. I wanted badly to be able to carry out these tasks, to create my own balloon mission and to reach the stratosphere.
But I hadn’t enough electronics skills to be able to successfully create this these devices.
Searching the web I found Oyvind’s ebook «Creating Cheap Circuit Boards», and that was kind of an epiphany to me – the simple techniques he taught in that ebook, from the idea to the finished circuit (fabricated PCBs included) enabled me to adventure in my childhood’s desire: get near the space…
The Aleph Flight Data Recorder Project
In this project, I have adopted an iterative development strategy. The first iteration will be all about creating the circuit’s base, as well as including a RTC clock and an onboard temperature sensor. I am going to focus mostly on the circuit design and implementation, and in another article I will talk about the software design and engineering process.
As I learnt from Oyvind’s ebook, Getting Started With Electronics, I can use the component’s datasheet to discover important information, as the voltage, temperature limits, and most important of all, a schematic of the typical circuit.
I got DS1307’s and LM35’s datasheets, and there I got the schematics for their typical circuits. These layouts are pretty straightforward, and my main job was to integrate these two little circuits into one layout, and set a way for the board to communicate with the Arduino microcontroller.
So I started out hand-drawing the two schematics, and connecting them in the supply lines. For both these integrated circuits, the input voltage is +5V. So they could share the input voltage and the ground. I also added an LED indicator, to show me when my circuit is on. I finally drew the connection from these components to a male header bus, to connect the board to the microcontroller.
With this schematic in hand, I drew it in Eagle and generated the circuit board to send to a fabrication facility. There are plenty of fabrication services out there, which are not expensive and suit well for a hobby project like this one. You can find some suggestions in Oyvind’s article Cheap PCB Design Process.
Some important “extra” things I decided to put in my layout:
First, I wanted to draw a ground plane, to make all components share a common reference potential, but also to simplify the traces’ routing, by connecting each component’s ground directly to the ground plane.
Another thing I wanted to include was the mounting hole spots. In my prior experiences with a PCB design the thing that I regretted the most was not having a spot to mount my boards – so I had to improvise, and I hated the results I got from this… :)
I am now looking forward the next iterations for The Aleph Near Space Project, and some of the things I am planning to incorporate are:
- Add new sensors to the circuit: external temperature, air humidity, air pressure, altitude, magnetic field, etc;
- Store data in SD Cards;
- Software’s parameter storage in EEPROM;
- LED/OLED display;
- Solar cell or LiPo battery powering options;
- Wifi config interfaces;
- design an Arduino clone in the circuit board, to have autonomous life without the extra microcontroller board!
Well, for the first iteration, that’s all I’ve got to tell. If you are interested in the outcome of this project, or if you would like to get involved in it, you are very welcome to contact me – please, send an email to [email protected]
And here is the link to the github-page with the schematics and firmware: https://github.com/juliozohar/Aleph-Flight-Data-Recorder
Thanks a lot!