atomic_fungus (atomic_fungus) wrote,
atomic_fungus
atomic_fungus

#6508: Well, now what do I do?

So, primarily from boredom I went into the basement and did a little poking around.

First up, move the two comic boxes which had been sitting on the old console stereo. First one I grabbed had Sailor Moon and Tenchi Muyo books, individual issues. Not sure how long I was collecting the damned things but it was long enough to fill a short box with those two series.

Other one was individual issues of Ranma 1/2, and then the prize find: Knights of the Dinner Table, issues 6 through 65. That's approximately half of my KoDT collection; in fact it might be all of it, because so far I have been unable to find the box containing the other half. I fear it might have inadvertently got tossed out, which would suck most egregiously. Here's hoping it wasn't.

Anyway, that done I started poking around for other things, and finally decided to see what was in the various boxes on one of the shelving units. There I found two C64s, two 1541 disk drives, and a total of four C64 power supplies.

Why four? I don't know.

...so I decided I'd have a look at the things and scope them with a multimeter and see if any of them were any good.

Apparently not. Three of the four reported no AC between pins 6 and 7. The one that did have AC there was running at 12v or a bit more. The 5v rails on all four supplies worked fine.

*sigh*

Since 90% of the computer runs on 5v that's okay, but without the AC input, the sound chip won't work, and from what I've read about the C64 power supplies it looks as if the clock signal is generated from the AC frequency, somehow or other.

One of the supplies which supposedly had a dead 9V rail nonetheless threw sparks when I accidentally shorted them together. It did so more than once, because I am fumble-fingered. The schematic for the power supply shows a 3A fuse in the 9V rail; a couple of sparks from a slipping probe shouldn't pop that.

Argh etc.

Now, the funny thing is, I could easily build a power supply for a C64; it's honestly a trivial exercise to make one:



The hard part is getting the right transformer--and even then, in the absolute worst case I could just use one to convert 120V AC to 9V AC and use that to drive both the AC circuitry in the computer and to run a DC power supply that would regulate it down to 5V. The real problem there is that the schematic I found calls for 1A at 9V AC, but 7.5A at 5V. Yeesh.

That's rather far outside a 7805's specification.

But! Read the fine print and you find that only 1.5A at 5V is required, and the schematic should read 7.5VA, not 7.5A. That's easier. I think it's still outside what a 7805 can handle, though I wouldn't put money on that. And there are ways to handle that issue, even so.

...whoever did that schematic is on drugs considering that the regulating component is not a simple transistor--cannot be, it's physically impossible--but an actual voltage regulator.

And any fool with basic electronics knowledge can build a power supply using a linear regulator. It's dead simple, and the hard part is making sure you don't short anything and that you have a good heat sink for your regulator.

But, what the hey--I can do that later. Right now--

I took out the 1.5v regulator board that I got from Fry's earlier today, to check it out, and ended up hooking it up with 12V DC input from a power brick, a connector I found in my project box, and just jamming the wires into the power clips on the MP3 player.

It works. It works.

I'm getting 1.49V out of the regulator with the 12V input, and the MP3 player is working as if it had a battery installed.

So the next step is to jigger up some kind of adaptor--something that will be about the size and shape of an AAA battery, but which will have the wires from the power plug soldered to the ends. After that, I need to work out some kind of enclosure--but that can be anything that comes to hand, like a pill bottle or an old plastic paperclip box or something. After that, mount it all in the Jeep. Whee!

...as I said, just in time for me to no longer have a commute.

ADDENDUM:



The power supply board and the MP3 player in question.
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