Imagine if Commodore had shrunk the 1530 (C2N) Datasette, the standard data storage device for the legendary Commodore 64, using microcassette technology. Thanks to TechTuber Bitluni, you don't have to just imagine such a device, he's designed it, built it, and successfully tested it. The intrepid electronics wizard even has plans to make it into "an entire C64 emulator with games," but that would be another episode.
On the technology that mates audio and data streams, Bitluni interestingly compared the relationship between someone playing piano and the sheet music which they read. “Beethoven himself achieved a decent data rate this way,” is a quote I never expected to transcribe today.
With the aim to get the best practical result from the Olympus microcassette hardware, Bitluni decided to design his own custom PCB with:
- A 16-bit DAC (or optionally two 8-bit ones)
- Op-amps as buffers for the ADC and DAC
- Voltage dividers for controls
- Plus, a small prototyping breadboard area for future add-ons
With the finished PCB received back from the manufacturer, we next see Bitluni populate it with a USB-C port, and a range of other key ICs he’d selected. The board powered up and worked first time (as far as we can see) but the electronics wizard quickly swapped out the op-amps previously selected for being “garbage.” The replacement op-amp ICs (LM258s) fixed all issues.
Making the miniaturized reimagined Datasette
Now it was time to make a 3D printed housing for the C64 microcassette system, one that did justice to the original design. The print, produced using a Bambu Lab 3D printer, certainly does the job. However, Bitluni reveals that the multiple trial fitting and refitting of the components led to issues before the project was complete. Probably the worst issue was when the delicate Olympus flex PCB connector broke.
Repairing such tiny and fragile components is tricky, so Bitluni hedged his bets by buying another used replacement unit from eBay while taking on the fix. However, the damaged flex cable was eventually patched up by soldering 34 hair-thin wires.
With the hardware all working again, Bitluni switched his attention to the task of getting data to and from the cassette. For simplicity and efficiency, it was eventually decided to pivot to frequency shift keying and from using sine wave to square waves. Tuning this coaxed the system into working in real-time on the chosen microcontroller with the signal at 1,000 Hz.
Pac-Man says yes
Now for testing, and Bitluni’s first attempt to store then load an 8KB Pac-Man game succeeded. Bigger games didn’t always work though, so the TechTuber decided to chunk the data into 512 byte pieces, and then write all chunks twice, “and it finally worked flawlessly.”
So, the final working tape system had a data rate (halved) 500bps, and a full 60-minute tape can hold about 1MB of data (but takes an hour to transmit) according to Bitluni. That is still impressive compared to the original Datasette, which could only "typically store about 100KB per 30-minute side," according to Wikipedia. Please note, though, that turbo tape software and fast loaders were available for the original Datasette, and they could boost the capacity of the original drive to approx 1MB.
Bitluni is happy with the project’s success, for now, but intends to make the microcassette deck appear as a USB-C mass storage device, and “maybe store an entire C64 emulator with games,” on a tape. The video ends with the tape deck-driven emulator ‘running Doom’ and some old C64 demos.
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