An A-SID trip, part 3

Posted by Stefano at 12/07/2022, 16:01:13 UTC.

This time I'll tell you about the hoops through which I've been going to run the program on real hardware.

Spoiler: it was an expensive nightmare leading to a huge final reward.

READY?

As soon as I moved back to Italy around Christmas 2017 I started shuffling around all the stuff I had left here. My childhood C64C was there too, among all other things, and I hadn't touched it until this weird A-SID idea came to mind. But now the time had come to fire up everything once again.

A few keycaps had been missing for decades and it was really dirty, but other than that it looked intact. I could also find the original PSU, a couple of QuickJoy Supercharger SV-123 joysticks in questionable conditions, a bunch of RF cables (who knows why I had many), all my beloved game cassettes, but no datassette unit. I plugged everything and started testing and all seemed to work, only the keys were quite hard to push (probably due to some rusty springs under the keycaps).

I had to find and buy a datassette unit now — here's where the problems began. I started looking on eBay and found that most such items were sold as "non working" devices (to avoid complaints and returns, I guess). I contacted a few Italian sellers who claimed to have tested the devices and asked them about some specific receipts that allow for cost deduction (yeah, don't get me started on the Italian fiscal system). Of course, they were thinking I was trying to scam them in some weird way, so I figured out they only sell to regular consumers. At the end I was lucky enough to buy a working 1531 datassette unit from Video Boy Club Roma who is probably the nicest seller I met in my life.

Once I got the 1531 shipped, I connected it to the C64 and it didn't work: no signs of life. I had an exchange of messages with the seller and tried to verify that the unit was actually being fed proper voltage and that the contacts were clean. While doing that I got a small electric shock from one of the joystick ports just touching it by chance and after perhaps a day the C64 wouldn't even turn on any more. I worried that my old electronic mate was dead or about to die, so I did a bit of googling and discovered about the PSU problems these old machines have and how fragile they generally are.

Long story short, the "brick of death", as people call it, was actually to blame. Luckily my C64 only reported no damage, only its fuse had blown. I bought a modern PSU replacement from Electroware, which ended up solving all power supply issues and made the datassette unit finally work.

However, the project had been at risk and I panicked somewhat. In order to avoid finding myself again in a similar situation I embraced redundancy and bought one more used C64C, a brand new Atari-style joystick, and an immaculate Methodo Model-1003 datassette unit. And since I was there, I also bought two breadbin C64s, each with its own original PSU (FWIW), in case I wanted to analyze/emulate MOS 6581 SID chips in the future — unluckily one of the two has a fried SID chip. Here's the whole team together (original PSUs apart).

TV, cables, and audio cassettes

At first I used an old bulky Philips CRT TV via RF that I had lying around, but at some point it just stopped working. Of course that happened the only time in about 30 years I needed it for something semi-serious. To maintain an authentic 90s vibe, I decided I would replace it with a smaller CRT. I discovered only after buying it that its remote was broken and also absolutely needed to tune channels. Obviously. Luckily it had a SCART input socket taking composite video.

Building breakout cables as detailed on the product page was relatively straightforward instead. Anyway, I took the occasion to throw some more money at a new third hand tool to ease holding parts while soldering (this saved me some time, especially for the A/V cable).

Finally, the audio cassettes. It seems they no longer make them as they once did, speaking of audio quality. But that was not a big deal in my case as the datassette encoding relies on "ignorant" positive-to-negative zero crossing detection. The Commodore 64 Survival Manual suggests using ferric oxide Type I audio cassettes, and so I just found some currently manufactured ones, which worked as long as they were not recorded more than a few times.

I bought and used Remzi64's 1530USB to record the .prg file to the audio cassettes via WAV-PRG as explained, once again, in the product page. I haven't investigated this matter at all, but it seems to me that the device delivers 5V power to the datassette (it probably just forwards USB power), contains a cheap audio codec, and works as a USB class compliant sound card — the WAV-PRG program then outputs the audio representing the program, which is essentially maximum-amplitude pulses with different lengths, through the chosen sound card.

LOAD. PRESS PLAY ON TAPE.

Once all of this was sorted out, I could finally branch everything and use my beloved C64 as a wah. For real.

I just can't explain how stupidly happy and childishly excited I was while shooting the demo video (luckily Paolo was helping me with the recording and the editing, otherwise I would have just messed everything up).

Continue to part 4 >