Send a file to PC via Payphone

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Picture of File Transferring in Emergencies

Next time you go to a place in the world without an internet connection to save lives, make sure your laptop has some software installed. Also take a digital sound recorded, 3.5mm male to make cable and the headphones.

In my previous instructable, I was transferring files via radio by using morse code.

It was not practical, but it was fun.

There are other, much faster ways to transfer files via radio, but that’s for a future instructable.

Let’s have a look at how can you transfer small files to your computer from anywhere in the world.

I am not talking about using the internet, I am talking about file transfer via ordinary phone to your PC at home.

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Step 1:

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Before going somewhere far, you need to set up your computers.

Computer that will stay at home and the laptop you will take with you.

Computer that stays at home/office/lab

Turn on your computer, connect the mobile phone to the laptop’s Line-In/Mic-In port via 3.5mm audio cable. Install an app of your choice that can automatically answer a call. I used “Auto Answer Incoming Call” for Android. Make sure you turn off the sound and vibration mode. Run the “CallTTY” program and change the mode to “ASCII-7” or “ASCII-8“. Make sure your computer is not going to turn off or go to sleep.

Install a “Base64 Encode/Decode Utility” on the computer.

Computer that goes with you

Install “CallTTY” and “Base64 Encode/Decode Utility

Now you are ready to take the flight!


Step 2:

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After collecting important data about “insert the subject”, you might want to send it back home for your colleges to analyse.

If there is no internet connection, but there is a phone, it’s your lucky day.

For this project, I used a small “.png” picture (1.17KB.)
Copy your file to the “Base64” program’s folder. My file was “STF.png” Drag it on top of the “encb64.exe” file. Bas64 encoder will create a new file called “name.OriginalFileExtension.b64“, so in my case “STF.png.b64” Newly created file, will contain a lot of symbols. Change the files extension to “txt“, in my case “STF.png.txt“.

Open that text file and Add a line at the top and a line at the bottom, containing text of your choice.

That text can help you to understand where code starts and where ends in case of any problems. It will also separate the information, in case you want to send more than one file.

I added “StartStartStartStartStartStartStartStart…” at the top and “EndEndEndEndEndEndEndEnd…” at the bottom.

Save it!


Step 3:

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Run the “CallTTY” software and change the “Mode” to the same your computer at home is set to – “ASCII -7” or “ASCII -8

At this point you have a choice to use the laptop to send the information home or first, transfer information to the digital sound recorder.

I used a public phone, so it made sense to record information to the sound recorder.

Connect the sound recorder to your PC and press record..

Open the “STF.png.txt” file and wait until it goes through all the text.

It will make an interesting sound.


Step 4:

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When audio has been recorded, go to the nearest PayPhone and dial your mobile phone’s number at home.

Once you hear that the call has been answered, start playing the sound until it finishes.

CallTTY” program will record the sound via mobile phone and decode it.

I did some experiments and found out, that sometimes, it’s better if you start playing the sound for a few seconds, then stop, start again, stop and on the 3rd time play all the file.

Not sure why, but my sound was decoded bad if I transferred it straight away. When I did this play a few seconds -stop, play a few seconds-stop, play it all technique, file was transfected perfectly.

It might be because my file was not 16bit mono as advised by “CallTTY”. I also used unregistered version, registered version should unlock some features.

Now your colleagues can decode the file.


Step 5:

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On the computer at home, copy the information from “CallTTY” to the “Notepad” and only keep the text between “StartStartStartStartStartStartStartStart…” and “EndEndEndEndEndEnd…” lines.

Save the file in “base64” folder as “name.originalExtension.b64“, in my case “pic.png.b64“.

Drag the file on top of the “decb64.exe

A new file will be created – “name.originalExtension.b64.out“, in my case “pic.png.b64.out“.

Rename the file, leaving only the original extension – “pic.png“.

If information was transferred correctly, you should see your file.

It took me around 6 minutes to transfer 1.17KB picture.

If you need to transfer only a plain text (txt), you don’t need to use “base64” utility.

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