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
- Tapes
- 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.
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Signing UpStep 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.
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There are different ways of encoding the images. Some of the methods are better for long distance (DX) because the signal may take longer but the error correction makes for a better image on the other end.
I see no reason that a person couldn't transmit images like this across the telephone except for the limited frequency response of most telephones. But I've sent images across a room by doing nothing more than turning up the sound on the transmitting computer.
Maybe this will inspire folks to look into ham radio and how much it's changed with the advent of digital technology and help revitalize the hobby.
All in all, good job!
1) It required identicle equip on both ends.
2) Not everyone wants to be seen when they answer the phone (Woman with messy hair, or answering in the bath room).
Talking while a picture was being sent, messed up the picture. I don't rememeber for sure but I think it took 10-15sec for each picture to be taken and sent.
The software isn't for image capture, either. Hams usually send pictures of their setups, maps showing their locations, cute/funny pictures and the like. There's one guy out of Oklahoma who likes to send pictures of Christian iconography.
I do remember the first attempts at "video phones" and they tried to send images using a cross between SSTV and analog signals. It was a pretty abysmal failure.
If only I had a bunch of extra laser pointers.
http://www.youtube.com/watch?v=M9xMuPWAZW8
Berith, yeah! Modems in computers do that every time you download something. When we all used to use manual dial-up modems and the baud rate was in the bps and kbps range you could hear the same computer type noises emanating from your computer during dial-up. That was your computer communicating via sounds with the internet service provider or BBS.
If you want to communicate with someone on computers via phone lines, install a dial-up modem in each computer and play around with dialling one another and using the multitude of programs and games that support modem connections. It was great fun when online gaming was limited who you could connect to and who could get it to work :D
Another common instance of image data transfer over phone lines is the common household and office Fax (facsimile). This is the whole kit and caboodle built into a box on your desk. It scans your page, dials your intended recipient and transmits the image in sounds. The other box picks up the phone, lists for the sounds, decodes the sounds, then prints a facsimile of the scanned page. Brilliant! :D
The man painting the building is Bask. It's a picture I took of him while he was painting a building near my house. The other picture is just a random computer to fill space.
http://gizmodo.com/5807527/how-to-hide-secret-messages-and-codes-in-audio-files
Question: if you hook the exit from the cassette player to the input of the tv (where the antenna would go) would you see the image on your tv?
Slow Scan TV (SSTV) only translates the sent picture, one picture at a time, to Audio, then receives the Audio and translates it back into a picture. It only does one frame without any voice or sound.
Unlike a television that receives and decodes audio and video up to 30 Frames in one second.
So, how did they use to see the SSTV images before the days of computers?
Great Questions!
Powerfool: to transmit an image you only need a little information actually. It depends on the size, variation of color or gray scale. Unlike a computer that divides the screen in to little dots called pixels. Old tv's divided the TV into lines actually one line that started in the upper left corner of the screen and descended in a zigzag pattern toward the bottom. The second scan started in the top middle of the screen and interlaced or was place in between the first lines. Each screen or frame equaled 525 lines and, on tv's, the scan rate is 15,750 Hz. Imagine as the scan starts you turn on the beam or turn it off. That is what TV's and Slow Scan do Slow scan is just slower. TV's are more complex due to how the information is rec'd, and the resolution.
That's why there's so many different modes of SSTV. Most of the modem manufacturers decided to make their own modes instead of just use the ones that were already around.
Great instructable!
It has brought up some great questions.... By the way modem stands for Modulate - Demodulate MOD - DEM drop one "D"
To transmit information you must somehow modulate then demodulate. So Modems have been around as long as transceivers.........
Keep up the good work.
- Phil
If your computer runs windows, you can run a program called sexpots.exe, which forwards all incoming calls to a port on your computer. It's pretty fun to play around with.