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ZX81 P and O filetype added to TZXDuino with a slight speed update.

ZX81 P and O filetypes have been added to TZXDuino. There is also a minor speed update that shaves a few seconds off previous load times.

We were hoping to have an update to CASDuino with working Dragon CAS files but unfortunately whilst we can get Chucky Egg to work we still can't get others to work. We are still working on it though.


  1. Hope to try this next weekend on my ZX81 (and Spectrum 48k). I modded v1.3 to work on my Arduino Mega with LCD Keypad shield - need to add the amplifier but for now it works with a headphone;)

    1. Nice. Do you have any photographs? It's always good to see other peoples versions.

  2. I made a short video of the Ardiuno with shield working:
    When I manage to test it with my spectrum I'll take more pics!

    1. That looks great.
      The amp will be needed I suspect but I do know that many have tested theirs with the ZX81 and have had good results.

    2. Sure I have a few audio Amp ICs lying around (TL081 LM741 etc) - I will add one with adjustable gain (I have a small pcb somewhere which I used as headphone preamp) - will post my results.

    3. Excellent. Can't wait to see your results.

    4. Hi Duncan, I managed to load all the games I threw at it successfully without an additional amplifier. I just added a 2.2uF decoupling cap - here's my 48K loading a couple of games (with composite output mod):

    5. How did you connect the cap? That could be an interesting way to make things easier for people. I have to try that myself.

  3. The 2.2uF cap is connected in series with the digital output of the Arduino - positive on the Arduino pin which drives the output. I chose a rather small cap as the audio frequency of the output is in the 1-2 KHz range and this will definitely assure the signal. The Arduino Mega (as the Mini and Nano) outputs a 5V max "square" wave which is somewhat integrated by the cap smoothing it off slightly - this is a very high peak to peak amplitude, more than double than a headphone one (2.2V peak to peak on 600 Ohms around 1 milliWatt). The input of the Spectrum is in any case decoupled by a much smaller ceramic 100nF cap in series with a 10K resistor to ALU pin 28 so even connecting it directly should supposedly work though I have not tried it. One important aspect could be line noise or ground loops: if you power the arduino with USB and you don't have a good ground you could be introducing noise. I suggest using a battery powered Arduino (I use any LiPo 2 or 3S I have around) to avoid any ground loop related issues if you are in doubt, at least initially anyhow.

  4. Interesting. Definitely going to have to give that a try to see if it will work on my Speccies and MSX.


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