Very old project completed! Commodore's datasette + MSX work together

Door Alexey

Guardian (2400)

afbeelding van Alexey

04-07-2018, 01:39

I know, this is kinda nuts these days, when you have Carnivore, MFR and similar cartridges "all-in-one". But I really wanted to complete this project because it was idling for sooooooooooooooooooo long time...

It all started a long time ago in a galaxy far.... well, it actually started in Finland in 2008. The Carnivore was not born yet and the only option to load stuff into MSX beside a tape recorder was to use a disk drive, if you were lucky enough to get one. Most of my MSXs didn't have built-in disk drives. That is why the Caslink project was made. But that's another story...

I never had any special cassette devices to load stuff into MSX, so I was thinking of getting one. No, I didn't get a Sony or Philips datasette as they were not available or were pricy. Instead, I got the datasette from Commodore almost for free. Well, it was a neat device that was possible to control with the built-in relay inside MSX. Starting and stopping the motor on demand was a cool feature. The only problem was that I could not load or save anything onto a cassette. At that time I had a very rudimentary knowledge of electronics, so after a few unsuccessful tests I abandoned the project and put the datasette into the storage.

So it happened in 2017 in Nijmegen that someone gave me a Philips datasette for free (sorry, dude, I don't remember your name, but thanks a bunch!). I really liked the way device was made and its features. Then I remembered that I had had a similar device laying somewhere deep in the storage. You can guess what happened next. I took out the device from its box and started to look at the schematics. My yet limited knowledge of electronics was enough to understand that the device was using the digital way of playing and recording the stuff. So the levels of playback and recording should have been above +4.1v. That was a huge difference compared to the analog audio signals that were used in the MSX computers. The mystery of the 10 year old failure was resolved. The solution was starting to cook in the brains. And finally after a few days I came up with the simple solution for both playback and recording.

First of all, the output from the datasette must be brought to a reasonable amplitude. A simple voltage divider with 2 resistors did the trick. And I could finally load some games from cassettes into my MSX. Yes! The second step was to bring the output from an MSX to the amplitude that could be used by the 74LS14 chip inside the datasette. A simple audio amplifier would have been sufficient. I found some schematics online and tried to implement it. Guess what - it didn't work. The amplifier was not giving out a reasonable amplitude no matter how I tried. I watched some tutorials on how audio amplifiers are made and tuned, tried a few ready-made schematics - nothing worked. The amplifier was giving a constant 0.6v on the output pin. That was obviously not enough to drive the TTL logic chip. I finally assembled the amplifier on the prototype board and started playing around with resistor values. I thought that 100 amplification level was too much. Yeah... How about 5000? At least that's the calculation based on the resistor values that allowed to reach an acceptable TTL levels for the 74LS14 from the amplifier. And finally I could save something from MSX onto the cassette!

The last step was to find the acceptable wiring of the 2 buzzers and install 2 switches to enable/disable them if the sound gets too boring. Then packing all that stuff into the datasette and closing the case was done. And voila! Now I have completed the project that was idling for 10 years and I am very happy to achieve this small, but nice goal.

Btw, the device is powered with a simple USB cable that can be inserted into a USB3 hub or a mobile phone charger. Very convenient.

Here are 2 videos showing the device in action:
https://youtu.be/yGTAUawP4UU
https://youtu.be/0PaZHA7I6UM

Here are some pics of the device:




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Van hamlet

Scribe (2539)

afbeelding van hamlet

04-07-2018, 08:56

What a nice project! Thank you Alexey!
A cheap, color matching device for the beige SVI machines, hm?
Now I wish to have an adapter for my 1541s Big smile

Van gdx

Prophet (3046)

afbeelding van gdx

04-07-2018, 08:58

Congratulations! You are very perseverant.
Do you have plans to share this work?

Van Alexey

Guardian (2400)

afbeelding van Alexey

04-07-2018, 10:50

Sure, I need to draw the schematics. Those devices were produced in large numbers. So they are available today at low prices.

Van Alexey

Guardian (2400)

afbeelding van Alexey

04-07-2018, 23:55

Ok, here are the schematics and the partslist:

http://podrezov.com/ds/partslist.txt

Van OmaiGodman

Resident (59)

afbeelding van OmaiGodman

05-07-2018, 10:12

If it wasn't for the fact that I already have a Philips data recorder I might actually have attempted this with one of my C64 datasettes LOL! Nice project and well done on finishing it Smile