Sunday, 25 August 2013

Modifying the C64 datasette for audio in [Modifications]


Cover art

Little bit of back story on this one...

I am a tight git and refuse to spend more on an SD reader for my C64 than I would on my entire wardrobe. Eventually I'll give but right now it simply isn't an option.


I found an alternative that worked quite well. I have been using my smart-phone to load games with a in-car tape adaptor in conjunction with the Android application 'TapDancer'. The app converts tape files into audio which goes through the tape head and hopefully loads the game...



The use of the word 'hopefully' is used deliberately here.

I found this was great when the datasette's 'heads' were aligned correctly but they don't stay that way for long, eventually the tuning screw comes loose and the whole process has to be repeated. It is even more annoying than tape loading.

last time I tune these bastards,


I figured the equipment/wires between the head units and the circuit board could be intercepted so I set about dismantling the datasette, and in doing so discovered the drive has 3 sets of wires leading to the board. these are;

  1. Common ground
  2. Data in [Playing]
  3. Data out [Recording]

notice the labels on the edge.
I then flipped the board over and traced the contacts where the wire met the board and found 3 large solder-points I could use. In theory you could also capture data from the C64 if you utilised the data out point, but I have no use for this function.




So I soldered wires to the ground and the data in points and made a rudimentary head phone jack from a 'choc block'. In the near future I will add an actual headphone socket but for proof of concept its OK.

Just follow the wires through the board. 

Ghetto phone jack. Capacitor helps a little with volume.

When I had adjusted my volume levels appropriately it worked perfectly.


I hope this is of some use to someone, I know I was looking for a while for a solution until I just caved and did the ground work myself. Its not perfect and I did have to find the perfect volume on my smart-phone to get the C64 to find the incoming data clearly.


If you try this, do so at your own risk, what you do with your old shit is your own business! 

~Anton


11 comments:

  1. I have a revised guide coming soon that strips the board down to essentials and no longer requires the rest of the datasette! Luckily I had 1 that no longer worked but after a fiddle I got the controller board working and bypassed the switches.

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  2. A while back I made some SD2IECs (http://www.c64-wiki.com/index.php/SD2IEC), which lead to a couple spare pcbs I got for free. If there's interest, I'll send one over for free.
    Cheers,
    Luke

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    1. That's amazing! I certainly would love to tackle that project! Contact me via antonmacarthurATgmailDOTcom and I'll sort out the postage costs.

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  3. I wish I were this adventurous the last time I was near a Commodore 64... We could have played Elite! ....

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  4. I've tried this on my unit, but so far no luck. It feels like I'm pretty close as I sometimes get the computer to recognise something, although pretty scrambled. What kind of capacitor did you use?

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    1. I later revised the unit to use a resistor, cant remember off the top of my head its values. Adding a resistor instead of a capacitor allow me to push higher volumes to the unit without it freaking out. For example I had the laptop set to 50% volume but afterwards I could push volume to max and not get any misreads. Sorry its not much help. I did find this post on Atariage they may be of help though http://atariage.com/forums/topic/210630-atari-cassette/?hl=%20cassette#entry2730286

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    2. Ah, right. I've already tried a number of resistors from 1k to 15k without luck. But it's good to know you went that route too, What's odd is I get pretty good reads with a crappy magnetic tape adaptor, but I'd love to skip this link in the chain. I've also tried reversing polarity obviously. Time for more tests tonight :)

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    3. I've been thinking a bit. After I get the volume level right with a resistor, I'll try adding a capacitor in a high pass filter configuration. After some googling I've found out that cheap tape decks could only reproduce frequencies as high as 12kHz. Maybe there's something above that in my supposedly clean signal, the Nyquist frequency and all that, that's destroying my signal.

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