Joe Zwerko
Experienced Member
- Joined
- Dec 17, 2009
- Messages
- 125
Hullo all,
For a while now I've been working on a replacement for the Expansion Interface, which I hope will be of value since the originals are harder to obtain than the keyboard units. The PCB design, for all intents and purposes, is done. I've put a PDF of the layout here (the file is too large to upload to the forum) so you can see what I'm talking about:
http://BartlettLabs.com/mire1.0 - PCB.pdf
The PCB is roughly 7" wide and 6.5" deep including the edge connectors.
I know I've mentioned this on the forum previously, but here's what it implements:
The vast majority of the stuff it implements has been finished for several years now; it was only a couple months ago that I decided exactly how I wanted the SD floppies to work, and wrote the software to do so.
Anyway, before I spend the money on fabricating PCBs and obtaining components, I need to decide what to do regarding an enclosure for this device. All along I've been assuming I'd figure something out, but I never really did.
The reason an enclosure is important is that many owners of this thing will want to use their original CRT monitor. However, the MIRE (that's the code-name for the new device, not 100% sure what it stands for yet) will want to physically sit where a real Expansion Interface would. Therefore, whatever type of enclosure is created, it must: 1) be physically large enough to support a CRT monitor, and 2) be physically strong enough to support a CRT monitor.
I guess I was assuming that 3D printing would somehow save the day, but I think requirement #1 above means that would be impractical due to the large size required.
There's no conceivable way this thing will fit within an available standard project box due to the locations of the mounting holes and the many connectors/cables. Sure, I could make the PCB a lot bigger to fit some standard enclosure by moving the mounting holes, but the cost of the larger PCBs would likely become enormous. It's already pretty big as it is.
I've heard about solvent welding construction and T-bolt construction, but I'm an absolute novice at enclosure-building and those seem beyond my capabilities. And another thing: I'm not saying I'll be the one designing, building and selling enclosures. I'd be very happy if someone else wanted to do that, thank you.
The only idea I've come up with that seems practical and somewhat affordable isn't really an enclosure per se. A large (about 8x16" like a real EI) slab of 1/4" thick Lexan polycarbonate with leg hardware holding it up to support the monitor. Possibly a second, thinner sheet of lexan below to which the PCB would be mounted. This would at least allow for easy egress of the various cables attached to the MIRE. However, this has its drawbacks:
I've been asking a few knowledgeable people for ideas and opinions, but nothing so far has jumped out as the ideal solution. So I'm bringing the question here to the Forum. If you've got some ideas or feedback, we can discuss it here or we can do so by email. Let's keep it to the enclosure discussion, please; if you have questions or concerns about the design choices I've made let's use a separate thread or email.
There's still some work left to do, for example I need to install a bootloader in the PIC processor (used for the SD floppies) so you can update it from the TRS-80 without using a programmer device. I also need to expand the SD floppy app for full-screen operation. Neither of these will hold up the build like the enclosure question.
Pete.
ps. I haven't yet sent out a call for Beta testers for the MIRE, but if you're interested drop me a line and we can start discussing it. I'd like to keep it to maybe 3 testers maximum. In exchange for your help you'll have the option to buy your MIRE at a deep discount, although I have no idea what the retail price will be yet.
For a while now I've been working on a replacement for the Expansion Interface, which I hope will be of value since the originals are harder to obtain than the keyboard units. The PCB design, for all intents and purposes, is done. I've put a PDF of the layout here (the file is too large to upload to the forum) so you can see what I'm talking about:
http://BartlettLabs.com/mire1.0 - PCB.pdf
The PCB is roughly 7" wide and 6.5" deep including the edge connectors.
I know I've mentioned this on the forum previously, but here's what it implements:
- 32KB SRAM (can be disabled for those with keyboard memory upgrade mods)
- Single/double density, single/double sided floppy controller (card edge or box header on the right rear)
- RS-232 (9-pin DSUB connector on the right side)
- Basic one-directional printer port (25-pin DSUB connector on the left)
- Cassette sound output (RCA jack on the left rear)
- Expansion port (card edge or box header on the lower right)
- SD floppies, mounted from DMK files on a FAT filesystem, which can be intermixed with real floppy drives
- Heartbeat interrupt
- and probably some other stuff I've forgotten...
The vast majority of the stuff it implements has been finished for several years now; it was only a couple months ago that I decided exactly how I wanted the SD floppies to work, and wrote the software to do so.
Anyway, before I spend the money on fabricating PCBs and obtaining components, I need to decide what to do regarding an enclosure for this device. All along I've been assuming I'd figure something out, but I never really did.
The reason an enclosure is important is that many owners of this thing will want to use their original CRT monitor. However, the MIRE (that's the code-name for the new device, not 100% sure what it stands for yet) will want to physically sit where a real Expansion Interface would. Therefore, whatever type of enclosure is created, it must: 1) be physically large enough to support a CRT monitor, and 2) be physically strong enough to support a CRT monitor.
I guess I was assuming that 3D printing would somehow save the day, but I think requirement #1 above means that would be impractical due to the large size required.
There's no conceivable way this thing will fit within an available standard project box due to the locations of the mounting holes and the many connectors/cables. Sure, I could make the PCB a lot bigger to fit some standard enclosure by moving the mounting holes, but the cost of the larger PCBs would likely become enormous. It's already pretty big as it is.
I've heard about solvent welding construction and T-bolt construction, but I'm an absolute novice at enclosure-building and those seem beyond my capabilities. And another thing: I'm not saying I'll be the one designing, building and selling enclosures. I'd be very happy if someone else wanted to do that, thank you.
The only idea I've come up with that seems practical and somewhat affordable isn't really an enclosure per se. A large (about 8x16" like a real EI) slab of 1/4" thick Lexan polycarbonate with leg hardware holding it up to support the monitor. Possibly a second, thinner sheet of lexan below to which the PCB would be mounted. This would at least allow for easy egress of the various cables attached to the MIRE. However, this has its drawbacks:
- Since the PCB is smaller than the lexan shelves and must be mounted toward the left, the RS-232 connector would be hard to reach. Perhaps the thing could be delivered with a short extension cable ending in another 9-pin DSUB connector that could be mounted to the back or front of the bottom sheet.
- There's nothing holding the CRT monitor in place; it would probably slide right off if bumped into.
I've been asking a few knowledgeable people for ideas and opinions, but nothing so far has jumped out as the ideal solution. So I'm bringing the question here to the Forum. If you've got some ideas or feedback, we can discuss it here or we can do so by email. Let's keep it to the enclosure discussion, please; if you have questions or concerns about the design choices I've made let's use a separate thread or email.
There's still some work left to do, for example I need to install a bootloader in the PIC processor (used for the SD floppies) so you can update it from the TRS-80 without using a programmer device. I also need to expand the SD floppy app for full-screen operation. Neither of these will hold up the build like the enclosure question.
Pete.
ps. I haven't yet sent out a call for Beta testers for the MIRE, but if you're interested drop me a line and we can start discussing it. I'd like to keep it to maybe 3 testers maximum. In exchange for your help you'll have the option to buy your MIRE at a deep discount, although I have no idea what the retail price will be yet.