CASDuino recording functionality

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Van CASDuino

Champion (268)

afbeelding van CASDuino

15-12-2021, 20:55

The MSX uses the Kansas City Standard for tape encoding.

Van RvS

Expert (79)

afbeelding van RvS

17-12-2021, 11:52

Danjovic wrote:

Hi Rvs
Now that I noticed that you are using the MIC output of the msx as a source for the recording. I was using a tape recorder, which provides a signal with greater amplitude but with more distortion. LOL!

Hi Danjovic,
Ok, I already thought you had a big amplifier in there... I never considered recording from actual tape. I am indeed (just) trying to record tape output directly from the MSX.
For recording from the tape recorder, I think the LM311 would work very well.
However, with signal amplitudes of a few volts, a direct connection to the Arduino pins (adc, comparator or digital) might work as well with very few additional components.

Van Danjovic

Master (212)

afbeelding van Danjovic

18-12-2021, 16:51

Hi RvS
I did my recording experiments with the cassette player because I had it in handy along with the FA-32 clone, but thinking it better, it makes more sense to let the legacy tapes to be decoded by a PC, a sound card and some audio tools.
In other words it the frontend for the Casduino recording should be ready to work with MIC levels (tens of mV) instead of Tape Recorder levels (Volts). That will require either a relatively fast rail-to-rail op amp (to work as an amplifier and as a comparator), or a more ordinary op-amp and a LM311.
As far as I understood you are having success with solely the LM358, right?

Van RvS

Expert (79)

afbeelding van RvS

20-12-2021, 15:58

Hi Danjovic,

Yes, the circuit works very well with the NMS8245. Unfortunately I cannot test it with other machines. What kind of MSX machines do you have?

I found the schematic from the handbook slightly confusing. It states 22mVpp - 7 mVpp in the schematic, but the circuit that is depicted below (and is used in the NMS8245) has double that value (~50mVpp at 1200Hz).

If you want the circuit to work at the range specified 22mVpp - 7 mVpp, you should change R2 to 330k and C4 to 22pF. Then it should work also for the very small signals.

Van Danjovic

Master (212)

afbeelding van Danjovic

22-12-2021, 19:02

Hi RvS
I have the Sharp HB8000, the Expert XP800 and the Casio PV-16, but I will only be able to perform some measurements on next february. If you count the FA-32 recreation it delivers a signal of ~20mVpp. I think it is safe to work with the worst case, 7mVppa and add some gain, then chop the voltage before applying to the comparator to get the square wave signal.

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