If you have some old cassettes, a computer, and a love for obscure technology, here's a fun project to waste a couple extra hours on. Using a type of amateur television broadcasting that dates back to the early days of space travel, you can store and view images from normal audio cassettes, using only your computer and a tape player. And once you've figured out what you're doing, you'll be able to transmit pictures on anything that's audio-capable. And maybe actually learn to use the technology for it's intended purpose.
Before you begin, here's a few things you'll want to have:
- A computer with a headphone and microphone/line-in jack.
- A tape player with the same jacks, and a record button
- The ability to work on a pointless, and mostly useless project
- A lot of extra time to kill
That being said, let's learn a few things about what we're going to be doing.
Step 1: Slow-Scan Television
What makes this project possible is a type of television called SSTV, or Slow-Scan Television.
With normal television, about twenty five to thirty frames (pictures) are broadcasted per second, making a moving image on your screen.
But with SSTV, there aren't any moving images at all. Infact, all you see in the end is one, still image, which is only about 256×256 pixels large. To most people that probably wouldn't sound very exciting at all, but for people like me, being able to transmit even one still image makes my brain jump with excitement.
Usually, SSTV is used by amateur radio enthusiasts, who broadcast an image that includes their callsign and other radio-related things over the HAM or shortwave radio bands. SSTV is even used on the International Space Station to broadcast images of the station back to earth, and to anyone who's listening in with a radio. But in this instructable, we'll be taking the audio signals that make up our pictures and recording them, instead of broadcasting them. Because radio transmitters are expensive.
Even though we won't be using it for it's intended purposes, the way we use it is exactly the same as if we were using it over the radio. We use a computer program to turn our images into audio, and also play audio to the program, which will then decode it and show us the picture that's encoded in the sound.
Step 2: Getting Started: MMSSTV
Ok, now it's time to actually get started on the project.
The main component in this project is a Windows program called MMSSTV. We're going to use the program to create our images, to turn them into audio, and to view images that are already in audio format. If you don't have Windows, there are Linux programs for SSTV, but I haven't played around with them too much. They should work about the same as MMSSTV though.
The first thing you'll need to do is, obviously, download and install the program. You can download the program here: http://hamsoft.ca/pages/mmsstv.php .
Once you've installed the program, start is up. But be warned, it's going to look very overwhelming at first. Just stick with the instructable, and you'll soon have a small understanding of what half of the things in the program mean. But most importantly, you'll understand how to use it. Hopefully.
Once you've played around with the program a little, move on to the next step to get started on your image.
Step 3: RX, TX, and Robot 36's
Like I said in the last step, looking at MMSSTV is probably giving you a headache if you've never had any experience with something like this before. But don't worry, it's not as extremely confusing as it looks. If you have no clue what you're doing, here's a very simplistic explanation of what you're seeing on the screen, and what it does.
- Orange Bar in the Top Right Corner - This is a spectrum analyzer. In a way, you can think of it as the wavy line on an oscilloscope when you play music through it. It'll show you what's going on with the audio. You won't need to know too much about it, only that when it's moving, there's audio either playing or being heard by the program.
- "RX Mode" Boxes - These boxes set what SSTV mode the incoming video is encoded in. Each mode supports different colors, sizes, and other aspects of pictures. Just leave this on Auto, and you'll be fine. The program will detect which mode the incoming video is in.
- "TX Mode" Boxes - These boxes set what mode you want your picture to be set in. Read about the different modes, and pick which one you think will work best for your picture. I usually use Robot 36 or one of the Martin's. You can read about the modes on the SSTV Wikipedia page.
- Big White Square With Tabs At The Top In The Top Left Corner - This is what you'll be paying the most attention to. Think of it as your work space. Each tab does something different, and you can use the tabs to do everything you need to do. All you really need to know is what each tab does, and you can use the program. Here's an explanation of each tab, and what some things mean.
have to worry about this tab when you're not receiving a video, but if the video you're decoding has a weird
tilt or slant, this tab can be used to fix the picture. Right click on the smiley face to fix your slant problem.
RX - This tab will show the picture your receiving/decoding. You can ignore the other buttons in the tab, all you need
is the empty white square. It's where the picture will show up.
History - This will show you all the images you previously decoded/received. It's pretty self explanatory.
TX - The TX tab is the tab you use to convert your image to audio. The picture you put together in the Template
tab will show up in the white space. When you're ready to turn the picture into sound, just press the red
TX button on the bottom of the tab and listen. The spectrum analyzer will move around, and a scan line
will move down the image. When the sound stops and the line hits the bottom, the audio is done.
Template - This tab is where you put together your image. You can use the "Draw picture" button to load a picture into
the template, and the "T" button to add text. Putting together the image is pretty easy, and most of the buttons
functions are pretty obvious. If you want a blank template, just click one of the blank squares at the bottom
of the screen. When you're done with your image, just go to the TX tab to turn it into sound.
Step 4: Making It Happen
Now that you know how to work the main parts of the program, you should be able to figure out how to put the audio onto a cassette. But just incase you haven't figured it out, I'll tell you how to do that, and also how to get images off the cassette, or whatever you're getting images from.
Once you've got an image made up in your template, and you're back on the TX tab, all you have to do is record the audio onto a tape. Press the red "TX" button to test your sound, and if you start hearing tones and weird computer sounds, then everything's working. Use a Male to Male audio cable to hook up the headphone jack on your computer to the microphone/input jack of your tape player, start the tape recording, press the red TX button again, and let it play through to the end. Once the sounds played through, everything is done, and now you have an image recorded on a cassette tape.
To read the image off the cassette, open the RX tab in MMSSTV. Then, use the same audio cable to plug the tapes headphone jack into your computers line-in jack. Go to the Options tab at the very top of the program, and click "Soundcard input level...". Make sure the Line-in input is turned all the way up, and then you're ready to go. Rewind the tape to just before the image, and press play.
If everything worked right, then an image should start slowly loading in the white space on the RX tab. This is the image you saved to the cassette. If the image has a weird tilt or shift, wait until it's done loading, go to the Sync tab, and right click the smiley face. Now go back to the RX tab, and the picture should be fixed.
Step 5: Doing More
If you've read up to here, you should now be able to figure out how to make this project work. And if you got it to work, then you now have the ability to do so many more things. Why does the image have to be on a tape? Try and think of other things you could send your pictures through, like a telephone, or anything else that uses audio.
And if you enjoyed doing this project, you can always learn more about SSTV, and maybe actually use it the way it's normally used.
You can also keep poking around the program to find even cooler things that it can do. After a few hours of playing with it, you might be able to do even more than I can do with it.
If you want to read more about SSTV, you can read the Wikipedia article on it, which should be able to give you all the information you need. http://en.wikipedia.org/wiki/Slow_scan_TV