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Breakthrough: Transmitting digital data to a cassette and back

In my attempt to build open hardware and free software to store digital music on compact cassettes, I managed to achieve the first breakthrough in the software part: Transferring data from the computer to a cassette and back using GNURadio, a sound card and a tape deck. There are still a lot of errors in the received data with the current modem setup, but there is probably a lot of room for improvements.

The GNURadio flowgraphs are in the open-system-compact-cassette repository at in the subfolder "gnuradio-modem":

The transferred data contain a raw RGB image with 320x180 Pixels, 24 bits per pixel. The modulation method was BPSK resulting in a data transfer rate of 11,6 kbit/s. No error correction was used. The tape used in this experiment is a good chrome dioxide (type II) tape.

The images in this post show the original image (no distortions), the result when the image data is modulated and demodulated completely in GNURadio (some distortions) and the result of the data transferred to tape and back (lots of distortions).

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DIY Walkman attempt

Using this cassette drive in a car radio case, I'm attempting to build my own walkman / portable cassette player out of it. The goal is to get a portable cassette player that is serviceable and extendable using modular electronic circuits connected using standardised interfaces. The tape drive itself follows the KISS principle (simple clutch) and has many metal parts so that mechanical failures are very unlikely.

This is the plan for developing the electronic circuits:

- Step 1: Amplifier circuit with 3.5mm jack using the built-in potentiometer.
- Step 2: Advanced motor control circuit, including different tape speeds using the former radio band selection switch.
- Step 3: Digital motor speed control by using a 19 kHz pilote tone on the tape and/or motor rpm measurement.
- Step 4: Digital stream playback and/or tape recording circuit, if possible

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