Electronics > Projects, Designs, and Technical Stuff
Cloning a Commodore PET-2001
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kizmit99:
Wow! - that cassette interface is certainly more complicated than the one I'm using for my TRS-80 clone... 
It's not a direct copy of the original.  It's similar, but should be significantly less finicky than the original.



I'm amused that I ended up in a similar place to you on the small voice-recorder to replace the old cassette deck.  (Yes, I'm easily amused  ;))
Anyway, always fun to see more progress.  Thanks for sharing!


GK:

--- Quote from: kizmit99 on October 24, 2018, 11:37:45 pm ---Wow! - that cassette interface is certainly more complicated than the one I'm using for my TRS-80 clone... 
--- End quote ---


Well,  like I said; "this is the "deluxe" cassette port analogue interface"  :)

When I was prototyping my PET for expediency I soldered together a cassette port audio interface just as simple as yours, but it wasn't entirely reliable. And a mic.-level write signal won't suffice for a line-level input and vice versa. And it wouldn't load at all, let alone with complete reliability, from playback signals getting as bad as this: 

kizmit99:
Eek - I didn't notice first time around that you were trying to clean up Mic level inputs.  Not much signal to work with there to begin with!
Out of curiosity, did the original have to deal with Mic levels?  That seems like a pretty formidable task, I would have expected Line level inputs at worst.

Question for you -- are you able to successfully replay data that's been mp3 compressed?  I've been mostly playing with wav encoded files to this point, but having a 5Meg audio file encoding 15K of data seems like a bit of over-kill :)
GK:

--- Quote from: kizmit99 on October 25, 2018, 02:50:54 pm ---Eek - I didn't notice first time around that you were trying to clean up Mic level inputs.  Not much signal to work with there to begin with!
Out of curiosity, did the original have to deal with Mic levels?  That seems like a pretty formidable task, I would have expected Line level inputs at worst.

Question for you -- are you able to successfully replay data that's been mp3 compressed?  I've been mostly playing with wav encoded files to this point, but having a 5Meg audio file encoding 15K of data seems like a bit of over-kill :)

--- End quote ---


Writing to both mic.-level and line-level inputs; hence the switched attenuator in the write signal chain giving three different write signal levels.
I wanted the read input to work without complaint from a couple of volts down to 100mV input with a adequate safety factor. Bits start dropping out at around 10mV rms, (depending on the signal-to-noise ratio) so that's that spec. met.

The various models of the Commodore "Datasette" all communicate with the computer via TTL-logic signals. All of my recordings so far are in mp3 format - no problems at all.

I finished the unit off and started putting it to use this afternoon . The banana posts on the rear panel connect to the motor-control relay contacts and can be used if desired to auto-switch the motor of an external tape recorder. The "sense" switch tells the computer that play/record have been pressed. This switch is normally just left on to skip "PRESS PLAY ON TAPE" (load) and "PRESS PLAY AND REC ON TAPE" (save).





GK:
http://youtu.be/e4uILTKAoj8
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