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 Billy I: The 68K computer 
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 65
Hello Everyone!

I have made a bit of progress over the past several weeks. The motherboard is half way finished, I made a hard drive adapter allowing me to use laptop drives, and so far nothing caught on fire :lol: . But I have one little problem.

FloppidyDingo wrote:
I have also realized that my power supply is stronger than I thought.


This won't be the case once i start making add on cards. So I started to design my own power supply, 100% from scratch, no cheating. As I finish up a good portion of it, I plug it in for a test run. The fuse didn't blow, which is progress considering the last time I tried to make one of these things. But when I test the voltage coming from the output, I get zero. I checked my wiring at least a dozen times, checked voltages on the primary side, I checked my transformer's wires for opens ahead of time, and I just can't figure out what I did wrong. I'm basing the design off of this supply: http://danyk.cz/impulz_en.html, only changing some of the components due to availability and to make it output more power. Below is the schematic of my design, with the changes in red, and measured voltages in blue.
Attachment:
impulz.gif

The transformer is a bit different, with the core being toroidal instead of EI, and thhe secondary has 12 turns, to output 12 volts. I also redid the EMI filter to be more effective. Can someone help me point out my wrong? I really hope this is because of a dead transistor and not my circuit, because transistors are easy to replace. And I know the optocoupler and all of that is missing, I left them out until I figure out my issue.


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Thu Nov 26, 2015 2:13 am

Joined: Tue Dec 11, 2012 8:03 am
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Location: California
I do somewhat understand the operation, but not quite as well as I would like to. The main thing I can think of is to make sure you have the polarity of the 40z and 8z coils wired correctly.

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Thu Nov 26, 2015 2:58 am WWW
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Garth wrote:
I do somewhat understand the operation, but not quite as well as I would like to. The main thing I can think of is to make sure you have the polarity of the 40z and 8z coils wired correctly.


Yeah, that might be helpful (facepalm). I'll fix that and see what happens.


Thu Nov 26, 2015 6:41 pm

Joined: Tue Dec 31, 2013 2:01 am
Posts: 112
Location: Sacramento, CA, United States
Forgive my ignorance if I'm on the wrong track, but isn't the "missing" opto-coupler a crucial element of the feedback control loop? Without feedback, how can the circuit be stable? Wouldn't it either shut off completely or blast uncontrollably? ... kinda like building an audio amp and "leaving out" the volume pot, or building a car engine and "leaving out" the throttle plate ...

Mike B.


Thu Nov 26, 2015 8:33 pm
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barrym95838 wrote:
Forgive my ignorance if I'm on the wrong track, but isn't the "missing" opto-coupler a crucial element of the feedback control loop? Without feedback, how can the circuit be stable? Wouldn't it either shut off completely or blast uncontrollably? ... kinda like building an audio amp and "leaving out" the volume pot, or building a car engine and "leaving out" the throttle plate ...

Mike B.


The thing is, the voltage output is ultimately controlled by the secondary windings (approximately 1 volt per turn). The optocoupler is to fine tune the regulation. Without the feedback, the transistor will oscillate on it's own and output a constant voltage (for my design, about 13 volts).

This is inferred from reading the description for the original circuit. You might be right, though. It wouldn't hurt to add the feedback loop ahead of time.


Thu Nov 26, 2015 9:36 pm
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I made quite a few changes to the circuit. First off, I changed the 0.001uF capacitor to 500 pF, and I made a new transformer that is more stable in construction. After checking that I had the coil polarity correct, I plug it in for a test run. This time, the output is 0.3 Volts. Well, at least I'm getting somewhere. After checking the original diagram, I noticed that it was designed to take in 230 volts. The line voltage where I'm at is 120. Could it be that this thing isn't getting enough voltage? Perhaps if I bump up the auxiliary and secondary windings, I'll get more voltage out of this thing. What do you guys think?


Fri Nov 27, 2015 2:27 am

Joined: Tue Dec 11, 2012 8:03 am
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Location: California
For half the input voltage, if you were using the same core, the top should have only 1x40 turns, not 2x40. With a different core, you'll have to consult their data sheets, or make some measurements. I think the turns ratios would remain the same from one core to the other. I suppose the 1M resistor above the 1N4148 should also be cut in half, to 470K or 510K.

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Fri Nov 27, 2015 4:33 am WWW
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Garth wrote:
For half the input voltage, if you were using the same core, the top should have only 1x40 turns, not 2x40. With a different core, you'll have to consult their data sheets, or make some measurements. I think the turns ratios would remain the same from one core to the other. I suppose the 1M resistor above the 1N4148 should also be cut in half, to 470K or 510K.


I'll make those changes and see what happens. Thanks.


Fri Nov 27, 2015 6:59 am
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Hello everyone! Billy is nearing completion, and it is time to start writing code! For the BIOS, I'm just going to have it do a quick memory check, activate and configure hardware, check for add-on cards, then start searching the drives for a boot sector. That shouldn't be too hard. The real challenge will be the OS.

I haven't been able to find an operating system that fits my needs (Windows and Mac are nowhere near compatible, and they are both starting to suck concept wise. I've never been able to understand Linux, and all the other 68K OS's out there aren't compatible either), so I've decided to roll my own. I was thinking of making an OS that has the speed of Windows mixed with the portability of Linux. It's going to be multitasking capable. Alone, it won't be much, just a DOS-like console with no GUI. But you will be able to write "modules" to extend on the OS to give it other functionalities (such as a GUI, extending the application API, and any other bells and whistles you want to add).

I'll start with the base OS, then add a desktop and GUI, then keep adding to it to make it more like a full fledged OS. And who knows, if Billy's powerful enough, I may even make a voice operated personal assistant. Okay, maybe when I do a 68060 build. The entire system will be driver based, so if you want to run it on another 68K machine, all you have to do is create a driver set for that machine and then load it on. Best of all, IT"LL BE OPEN SOURCE!!!!! Yay!

I still haven't named the base OS, any suggestions? I'll name my first extension set "Sokudo" (Japanese for "speed"), because the one thing I'll ask my self when writing the code is "How can I make this run faster/more efficiently?" I hate slow computers, which is why I avoid the ones at my school. I want to bring out Billy's full potential. I didn't put all of this effort into a machine just to have it be slow at everything.


Tue Dec 01, 2015 2:04 am
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In another thread you said the 68K computer is "almost finished. Hardware wise. I just need to spend a good session or four to finish the soldering job."

I would have thought you'd be anxious to get that completed! :?: Don't you get itchy, knowing that right now your project hasn't run as much as a NOP?

Please remember to share photos as the work progresses. And did you get that PSU straightened out? I myself would just use a wall wart or a salvaged PC supply, but the choice is yours, of course.

cheers,
Jeff

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Wed Dec 02, 2015 4:14 pm WWW
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Garth wrote:
For half the input voltage, if you were using the same core, the top should have only 1x40 turns, not 2x40.
Instead of changing 2x40 -> 1x40, I'd be inclined to change the 2x40 -> 2x20. Either way the total number of turns is reduced 50%, so maybe it doesn't matter. But the builder of the original version made a point of splitting the primary into two segments, with the secondary sandwiched in the middle, physically. If that's a detail worth preserving (I'm not sure) then the low-voltage version would need 2x20 (2 segments of 20 turns each).

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Wed Dec 02, 2015 7:54 pm WWW
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Dr Jefyll wrote:
In another thread you said the 68K computer is "almost finished. Hardware wise. I just need to spend a good session or four to finish the soldering job."

I would have thought you'd be anxious to get that completed! :?: Don't you get itchy, knowing that right now your project hasn't run as much as a NOP?

Please remember to share photos as the work progresses. And did you get that PSU straightened out? I myself would just use a wall wart or a salvaged PC supply, but the choice is yours, of course.

cheers,
Jeff


I WAS going to use this new PSU so I can make the case smaller, since the PSU itself is smaller than the original, but then I had that same thought, so I put it on hold until the rest of the system is working. The original supply gives enough power for now, so if it aint broke don't fix it (I wonder how many people my age actually say that :lol: ).

I kind of can't use a wall wart because Billy requires 12 and 5 volts that can be turned on or off (the motherboard only uses the 12 volt, but the CD drive and hard drive use both), along with a 5 volt stand by. Oh wait, that's exactly what the original PSU is. A modified laptop charger. I could modify a PC power supply to work, I even made a 4 pin connector to fit in Billy's unusually shaped 12V input. But I don't have any extra power supplies that work to do that mod with. The new power supply that is on hold has a 4 pin, but it's not done (I have to rewind the entire transformer. Again.) I'll post pictures in a little of my progress in a little.

I made a laptop to desktop HDD adapter so I can now use that 20GB Travelstar I have sitting around. The adapter doesn't work in my real PC (UDMA-6 does not like impedance mismatched wires), but it should work in Billy.


Wed Dec 02, 2015 10:43 pm
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Here is a picture of me testing the power supply. The HDD spins up correctly, the CD drive can do it's... CD drive stuff, and the intake fan spins at full speed. I checked the voltages, and all regulators are fully operational (including the 5V switching regulators for the add-on slots, which is surprising considering I cheated and used an OP amp as a PWM controller). The parts are also placed where I want my proposed case design to have them. The HDD adapter is a bit bulky, though... I could just buy a smaller one off of eBay or something.
Attachment:
1202151611-00.jpg

I had to "jump start" the PSU because I had no power buttons on hand. That's why there is a cable coming off of it and going out of frame. That cable supplies the standby voltage and Power On signal. I also noticed that a spacer is missing from the PSU's metal shell, I should probably fix that before something disastrous happens. I've melted paper clips with laptop batteries, who knows what the charger will do.


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Thu Dec 03, 2015 12:26 am
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barrym95838 wrote:
kinda like building an audio amp and "leaving out" the volume pot.


Just had a flashback, I've done that before :lol: . It still wasn't very loud, though.


Thu Dec 03, 2015 12:34 am
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Joined: Thu Oct 08, 2015 11:57 pm
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So I have some bad-ish news. I'm going to have to take a break from Billy because I think I have minor lead poisoning from my solder. I'm showing about half of the symptoms. I'll resume my project when I feel better. But first thing I do is make a fume extractor. I have some old HEPA filters that I might be able to use. But you guys shouldn't worry about me, I'm sure a good several doses of vitamin-C will get me back in the garage in no time.


Sat Dec 05, 2015 6:45 am
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