Imagine that you can wear a device, capable of storing approximately 250,000 credit card numbers and use them wirelessly. Sounds ridiculous? right? right??

During last year, I have been working on different projects implementing sound to make monetary transactions: Raspberry Pi Zero or BlueSpoof.

But this time, I want to implement something that I can wear easily and discreetly. To make a project with these characteristics, I needed some elements:

Time ago, I was reading about a project to implement a SD card with ATtiny85 to play WAV audio files. I was preparing myself to try to replicate it, but I noticed that someone was already selling something similar at Tindie. So I decided to try it!



It works very well. These are its characteristics:

The SD audio player supports only RIFF-WAVE format sound files known as Microsoft wave file in LPCM, 8/16-bit, mono/stereo and up to 48kHz sampling rate.

  • MP3 files must be converted to the .wav file.
  • The player starts to play on power-on or card insertion.
  • Sound output is 8bit mono.
  • If a sound file directory “wav” exists in the root directory, the wave files in the sound directory will be played in order of directory listing.
  • If the directory “wav” does not exist, the wave files on the root directory is played instead.

Push button switch is to jump to the next file. Reset button to play the first file.

Player is without an amplifier, but can drive small speaker or headphones. Volume is enough for a small discrete desktop player or for night listening. Amplified speaker is recommended.

In my perfect scenario to convert magnetic stripe data to audio, an amplifier is a must! But this project does not have it. So I decided to use the WAV player without worry about the amplifier. What I did to balance the output was to use a “fine” coil.

After this video, I changed the output. So instead of using speakers, I adapted the coil to be more flexible:
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To keep it small, I used a LiPo 3.7v 120mAh. The software to generate the customized WAV files is in my repository: the ViolentMag or AudioSpoof.

After you generated the WAV files with your mag-stripe data, just copy and paste them in the SD Card, and you are ready to use AudioPay! Instead of connecting the speaker, add a coil and test it:

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Adding AudioPay to your projects, examples:



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