Satellite communications

Due to the lack of GSM coverage in many parts of the world (many countries and oceans) I looked for what global communications systems are available in the world.
The first I found is the HF Data Link band used by aeroplanes (3-30 MHz). It’s long range and covers the poles. Although it’s transmission speed is quite low it may be an option if permissions can be obtained and the antenna required is not too long.

The other system are satellite links, which allow voice and data exchange. The constellation INMARSAT provides much information about the products and services available. Nevertheless, they are mainly intended for industries, so M2M devices are hard to find (it exists something called IsatM2M that seems to be interesting). The device DMR-800D OEM looks good, since it’s designed for solar powered installations. Nevertheless I couldn’t find any information of prices, and in it’s weights is 190 grams.

With another constellation, called ORBCOMM, was much easier to find M2M devices.
According to Wikipedia the cheapest receivers cost around $100. Since I couldn't find it's exact price, the model I like most, the Stellar DS100, seems to be one of the simplest.
They say in its datasheet that it’s voltage input is 8 to 16 VDC, its max peak current consumption is 2.0 A (transmitting) and it’s nominal consumption receiving is 77 mA. It’s temperature range is also similar to the GM862-GPS (-40ºC to +85ºC).

Those are not the only constellations designed for communications (I also found GlobalStar, for example) but the devices I found in a brief research work with these two systems.

It’s good to know that this technology exists, but it’s still soon to consider the acquisition of any of those devices.

GSM around the world

I found this world map in PDF where places with GSM coverage are coloured in brown (and 3GSM coverage in yellow). It’s a quite big file (21.8 MB), but it seems interesting, since one of the problems the airship will face during its journey will be the lack of coverage (that may determine the route it will follow).


In the website where I downloaded that map I also saw an ad about global SIM cards. It’s called MobilityPass, and they claim their rates are much lower than any other roaming service. I haven’t check their rates yet, but this system (or any other similar done by any other company, if exists) can be a solution for the access to GSM.

RC toys

Communications will likely be through the GSM network (especially GPRS where available), but I found interesting to see how common RC toys work, so I opened the receiver to find out who was the responsible of sending and receiving those 27 MHz. when playing. After some time unscrewing I found that:


Two DC-motors connected to a green board. The top right black cable is the antenna, and the disconnected red and black cables at the bottom left is the power source. I didn’t manage to make it work, since I couldn’t find the transmitter and none of my other transmitters worked at the same frequency (I tried, but no positive result). But anyway I could read the name of the IC in the image:


It’s name is RX-2B, and reading it’s datasheet I could see that there’s another chip with similar name; TX-2B (the ‘R’ is from ‘Receiver’ and the ‘T’ is from ‘Transmitter’). It’s designed for cars, since it’s outputs are labelled as ‘right’, ‘left’, ‘turbo’, ‘forward’, etc.

Learning about cameras

I haven’t yet received the GM862-GPS chip, so I’ve been messing around with another important part of the project. Sometimes it will need to be manually controlled it has to carry a webcam. Since I have no idea of how webcams work (except from the view of the user, which is just plugging it to the USB port and start using it) I have to start by finding manuals to understand them.

Soon I found a type of cam that is all I needed; it’s lightweight, cheap, and very low consumption. Those are the so called CMOS Cameras, and they’re widely used in common webcams. Fortunately I had a USB webcam I've never used and that seemed perfect for learning. Once I opened I found the following:


First of all, those six LEDS are not necessary at all (they’re just to illuminate dark rooms). The camera itself is the tiny black square in the middle. Some CMOS cameras available in the Web have integrated lens, but mine not, since it was integrated in the casing. Because of that images are not on focus (unless I put the lens at the right height), but it’s working principle remains the same, so it won’t be a problem to understand how to communicate with it.

The best way to get started is to stop talking and start doing (Walt Disney)

So, let's go.
I will tackle the part I consider to be the hardest (maybe I’m wrong, who knows), and that’s the electronics part. It comprises both navigation and communications. For that purpose I found at SparkFun this kit to use the GM862-GPS chip. In two lines, the GM862-GPS is a communications chip (43 mm. each side) which is able to receive GPS signal. It has algo a built in Python interpreter (quite limited, though). I have some knowledge of Python, but I’ve never programmed a chip through the serial port. I printed a couple of the official manuals (the Hardware and Software User’s Manual) and I’ll try to figure out what can I do with that. It arrives this Friday, so till then I have some time to read the instructions (and prepare some exams, for September, too).

First doodles

I don’t have yet a complete mental image of the finished airship. At first I imagined something not much bigger than one helium balloon (two at most) but soon I realized that it would hardly carry the not-so-heavy navigation electronics. And since an integrated GSM GPS chip costs 120€ I believe that some extra weight for security systems won’t be a bad idea.

So, many different parts require my attention, and since I can’t solve them all at the same time, I should try to organise myself. Operationally I’ve divided the airship in two different sections that can be split in two subsections each.

1. Aerodynamics
a. Lift
b. Propulsion
2. Electronics
a. Navigation
b. Communications

In a general view, lift will be helium’s job, since I need some way to control height (maybe with vertical propellers or with some system to vary volume), propulsion will be carried out by solar powered and internet controlled propellers. It will navigate using GPS (cheap, precise and global range) and communications will use the GSM network (especially GPRS if available). It will be useful to send image using a CMOS camera, since it has to be manually controlled (on landing).