ALIEN – ALtitude Imaging Entering Near-space

March 27, 2009

Payload electronics

Arduino Duemilanove

Arduino Duemilanove

Given that its the beginning of the project, I thought I might lay out the electronic plans for the payload that we will be building over the coming months. The main brain of ALIEN-1 is going to be an Arduino Duemilanove, which we will hook up with numerous other goodies.

Arduino

We’ve chosen the Arduino because not only was it recommended to us by #highaltitude, but it has a proven track record and is great for first flights. Where it lacks in processing power it makes up in cost, size, and the ‘just-works’ feeling that you get with open source software and pure win. Plug in USB, program in C, go. One thing I will say, skip on the Arduino IDE and use vim like a real human. The makefile that they supply for typical commandline usage isn’t very good, and I personally use a custom-made script to build my projects.

The row of black plugs along the top are the 14 GPIO (General Purpose Input/Output; Digital) pins, of which 6 support PWM, ie. analoge out. There also is the AREF pin that you most likely will never use, and a GND pin next to output/input 13. GPIO pin 13 has a resistor attached by default, so you can plug in a LED between 13 and GND for the most basic of tests. Analogue inputs are on the bottom right, although we will most likely not be using those. If you run out the Analogue pins can also function as GPIO pins. Finally the middle-bottom block provides or recieves power to or from any peripherals you might connect, with power input (battery), ground, 5v regulated and 3.3v regulated.

The board is self-sustaining, and no messing with resonators, clocks, regulators or infact, electronic components is required. Its essentially an all-in-one mini-motherboard bundle, quick, easy to use and put simply, awesome. The processor is an AVR, which you can program in C, using libc-avr and avr-gcc. (Always a plus).

Just as a note, we chose this board over the pro or mini because it had the usb connection built in, and getting a pro+usb breakout would have cost more overall.

GPS

We’ve chosen the Trimble Lassen iQ, again for its proven track record. This device takes 3.3volts of power, and communicates over Serial, unfortunatly adding to the Serialdevice dilemma (below). Its also very small, but alike the arduino, may be difficult to mount onto a PCB, due to the nature of the connectors. Requires a good external aerial. In theory, this little thing should plug&play, requiring no setup whatsoever. I hope ;). We’ve had a very generous donation of one of these GPS units from ‘natrium42’ at electrobee.com, including antenna.

Radio

Forced to operate inside the radio bands that don’t require a licence, we’re using this little thing from Radiometrix, who have very kindly offered to donate one to the project. We’re sure that it will work fine, and it has been tested by UKHAS like all of the other components. When this arrives we’ll have a picture for you :). We’ve yet to decide what protocols we will use to communicate back to base, but I expect that it will either be, or be based on UKHAS’ standard. The arduino is able to generate a simple frequency or note on any GPIO pin so we will most likely be controlling it from there.

SD Card

In order to log GPS location and temperature, we will be using this adaptor. Thankfully this thing attaches to an SPI on the arduino, uses some of the GPIO pins and has a clock. Thank god! That means we don’t need to use the single hardware serial port for access to the SD card; meaning we can use it for access to the GPS or the Phone – see below.

Temperature Sensors

These sensors from maxim, to say the least, look very tastey. We also know that they will work with the arduino, but I plan to write my own library to attack the onewire protocol. This will be published when we’re done!

GSM

Most of the brainstorming is going on at the wiki, but Simrun owns a old Sony Ericsson w800i, which we plan to use as a backup to the radio. When the balloon has landed, the radio connection will be next to useless, so we will have the flight computer send us SMS/texts with its location. We’ve found this promising pin layout, and intend to buy a USB cable for the phone and then hack it with some scissors.

Serial Communication

Unless you plan to buy one of these pieces of awesome, you’re limited to just one ‘UART’, or Hardware Serial. Software Serial can be used, but you have to practically constantly poll for input. It looks like our payload will wind up with one device on Hardware Serial, and one on Software. We are yet to decide which will be which, but since the SD Card, Radio and Temperature Sensors all play nice, the contenders are the Phone and the GPS. GPS has precedence, and unless one of the devices desperately requires Hardware Serial to operate correctly, GPS will get it. Also, the AT protocol that we will use for the phone is very command-response based, so we should only have to poll for a reply after transmitting a command.

I will endeavour to update you as the components arrive and we get them set up!

— Daniel Richman

Advertisements

Leave a Comment »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Create a free website or blog at WordPress.com.

%d bloggers like this: