Alright, now that my head has had time to clear from this, I'm working on making a cleaned-up version of the schematic. Also, since the old schematic was done in DipTrace, and that's a commercial program, I'm re-doing it in the open-source program 'gschem'. I did use the freeware version of DipTrace to make the old schematic, but I just like the idea of releasing a schematic generated with open-source software.
EDIT: I'll post it when I'm done, so hopefully you guys can figure out if I'm doing anything wrong, or if there's an alternative approach that would work better.
Internal 512k expansion?
Re: Internal 512k expansion?
I haven't checked it too carefully, but here's my first try, exported as a PNG.
Re: Internal 512k expansion?
I asked an expert (Andrew Lynch) over at VCForum - he has a few projects under his belt, including the NV8EM computer and XT-IDE adapter. This was his answer:
Mike
"Hi Mike! I use KiCAD and FreeRouting.net for the PCB autorouting. Works like a champ but a significant learning curve. Let me know if I can help!"
I've never designed anything big enough to need software, but I'm willing to learn. And we have backup.Mike
Re: Internal 512k expansion?
I have KiCAD on my machine as well, but gschem was easier for me to get used to. There's supposed to be a way to make PCB designs using other products in the GEDA suite, but I haven't figured that part out yet.
EDIT: Oh, actually it's pretty easy. You can just import the schematic, place the components, and auto-route. I kind of wish I could figure out how to make it route without vias, though.
EDIT 2: GEDA PCB's auto router is seriously lacking compared to DipTrace. I guess it doesn't matter too much though, since I haven't successfully tested my design yet, anyway.
EDIT: Oh, actually it's pretty easy. You can just import the schematic, place the components, and auto-route. I kind of wish I could figure out how to make it route without vias, though.
EDIT 2: GEDA PCB's auto router is seriously lacking compared to DipTrace. I guess it doesn't matter too much though, since I haven't successfully tested my design yet, anyway.
Re: Internal 512k expansion?
Alright, I started re-doing my schematic on KiCAD, and discovered an error. A16-A19 are connected in reverse order to the 74154. This is probably also why when testing the upgrade (while it was working without the 74ls245 installed) I only got it to count to 448k.
Re: Internal 512k expansion?
I guess I like GEDA better than KiCAD. Schematics are about the same in both, but the options for PCB routing are clearer in GEDA.
Re: Internal 512k expansion?
Hmm, I'm wondering if I might be able to combine all the logic onto a microcontroller or PLD. That would reduce the cost of getting circuit boards printed (should the project advance that far) by quite a bit. I already had a design done where I did the address decoding with a PLD, but I still had the '373 latches and the '245 transceiver in the design.
Re: Internal 512k expansion?
I went back to DipTrace. 
It's just so much quicker than all the other offerings out there. If I were doing this to make money, I would totally consider buying a license for this program.
Anyway, I reconstructed the old design I had around the PLD, and I'm concentrating on squeezing it into the smallest space possible. Luckily, the DipTrace autorouter can work magic, and I can have all the chips almost touching each other. I have the board cost with BatchPCB down to around $16, or $31.10 with shipping and the $10 'handling' charge, assuming they're ordered individually.
I don't want to give anyone the purchase link until I have the design successfully tested on perfboard, though. The PLD code works in a simulator, but since I don't have the device yet, I have no idea if it'll work practically.
EDIT: Got the PCB below $15 now, so that's under $30 with the shipping and $10 handling charge. I think that's a good goal. The board is, of course, unpopulated in that state.
It's just so much quicker than all the other offerings out there. If I were doing this to make money, I would totally consider buying a license for this program.
Anyway, I reconstructed the old design I had around the PLD, and I'm concentrating on squeezing it into the smallest space possible. Luckily, the DipTrace autorouter can work magic, and I can have all the chips almost touching each other. I have the board cost with BatchPCB down to around $16, or $31.10 with shipping and the $10 'handling' charge, assuming they're ordered individually.
I don't want to give anyone the purchase link until I have the design successfully tested on perfboard, though. The PLD code works in a simulator, but since I don't have the device yet, I have no idea if it'll work practically.
EDIT: Got the PCB below $15 now, so that's under $30 with the shipping and $10 handling charge. I think that's a good goal. The board is, of course, unpopulated in that state.
Re: Internal 512k expansion?
I'm working on a PCB design for the CPU socket version of this upgrade again, using all discreet components, with KiCAD and FreeRouting. I believe that the design I prototyped should have worked, and I'm not sure why it didn't, so I'm hoping using a printed circuit board and new chips will clear up any problems. I'll probably be getting the PCB prototype from BatchPCB, or maybe PCBsingles, if I can make a decent one-sided design.
Re: Internal 512k expansion?
Alright, I expanded the circuit board to provide a full 736k, and I also discovered a great new option for getting PCBs made (at least if your size is less than 10cm x 10cm).
Check it out:
http://iteadstudio.com/store/index.php? ... cts_id=175
They're in China, looks like air mail to the US is $5, so $33 total for 10 boards! From what I've heard they get boards made up in about 6 days, and shipping takes 1 to 2 weeks. I've read some mixed reviews about them, but apparently you can get good results if you design with a few quirks in mind (I think my design will be fine without any modification).
At that price, I think it's definitely worth a shot.
Check it out:
http://iteadstudio.com/store/index.php? ... cts_id=175
They're in China, looks like air mail to the US is $5, so $33 total for 10 boards! From what I've heard they get boards made up in about 6 days, and shipping takes 1 to 2 weeks. I've read some mixed reviews about them, but apparently you can get good results if you design with a few quirks in mind (I think my design will be fine without any modification).
At that price, I think it's definitely worth a shot.