My own 8-bit RETRO Homecomputer: RhoCoCo

[mahjongg]

I just wanted something slightly better than my previous attempt (for my ZX81 clone, that used 6 x 6mm keys). Not something like an IBM bucking spring keyboard, or by using Cherry keys and Cherry keytops, but neither something really bad, like the dead flesh feel of a real speccy, or membrane keyboard.
Anyways, I will suspend my opinion on how well, or how bad the keyboard actually is until I have really tested the prototype.
These 12x12mm keys can be bought with several operating force variations, so I can experiment with that too.

Currently my plan is to use keyboard overlay (rub on) stickers, which should work, as the keytops are flat. With non flat keytops that would become impossible, and I would have to look at much more expensive solutions. This is a hobby project, mind you.

And yes, I have thought of replacing the current keytops for 3D printed ones, for about ten seconds, before rejecting the idea as too ambitious.
Not that it can't be done, but it would increase the price too much, and means I have to engrave the keytops, or print 40 or more different ones with different engravings, but then printing them with a high enough resolution so that you can integrate the imprinting will not be practical.

I try to keep to the KISS principle, as much as possible. Keep it cheap and simple....

[gordon77]

'Keep it cheap and simple....'

KICASS?

[mahjongg]

LOL.

yes, with Chloë Grace Moretz in the main role.....

But yes, I hope RhoCoCo does "kick ass".... Not as a high speed performance computer, but in the RETRO nostalgia and simple to use and fun department.
Its use should bring back memories of the C64, and Spectrum.
And hopefully you can build one yourself!
Still, there isn't even a working prototype yet, I'm still working on the bill of material, then I have to start writing software, so I can bring it up, lots and lots of work still to do.

[gordon77]

LOL.

yes, with Chloë Grace Moretz in the main role.....

But yes, I hope RhoCoCo does "kick ass".... Not as a high speed performance computer, but in the RETRO nostalgia and simple to use and fun department.
Its use should bring back memories of the C64, and Spectrum.
And hopefully you can build one yourself!

Interesting project, and l admire the amount of work you put into producing them.

[mahjongg]

As said, its a hobby project, I'm doing it all in just a few hours, every thursday evening at my makers club, revspace, in den Hague, the Netherlands.

[Gavinmc42]

Currently my plan is to use keyboard overlay (rub on) stickers, which should work, as the keytops are flat. With non flat keytops that would become impossible,

Not impossible just fiddly, those curved Alps keytops were a pain to do the rub on letters and symbols.
I can still remember doing it 38 years later, a good day was doing two or three key caps.
My ZX81 had what I now believe to be Alps keyswitches, no click but maybe 3-4mm travel.
My Microbees had nearly the same keyboards.

You would think it would be easy to make DIY keycaps these days.
Engraving flat keytops is probably the easiest.
Two ways I have used is the cnc engraving that uses two colour flat sheet PVC and laser engraving with two colout sheet acrylic.
Most trophy making places can do this, probably easy for the laser to even cut out the keys?
And lots of colour combos to pick from.

Those TACT type switches can get very tiring so perhaps the lightest force versions?
And maybe mount the whole thing with rubber or foam to allow some give?

Seen some DIY injection machines now, but still need a CNC mill to make the dies, DIY double shot keycaps?
DIY keyboards seems to have gone mainstream, bags of keycaps can be got in every colour now.
I have wasted days on this site
https://mechanicalkeyboards.com/
Apparently you can get testers with lots of diffrent keys, so you can choose the feel you like.
You can get wood keys and keyboards too, makes for easy laser engraving or even burning the letters by hand.
Bamboo mouse?

All because RPF brought out a mouse and keyboard I felt I had to learn about all this.
Pi's are more than just learning coding.

Soon I will be designing my next house around a nice Pi programming environment
I have already started on the furniture
Researching Manchester Victorian era upholstery patterns which led to learning something new or in this case old.
https://en.wikipedia.org/wiki/Worshipfu ... _Upholders.
Lots to learn about their craft.

[mahjongg]

Laser engraving is a good idea, we have a laser cutter/engraver at my hackspace, I could experiment with that.
Thanks for the idea...

[Gavinmc42]

Access to laser just made it a software issue.
It takes time to CAD but once everything is working you could have a dozen sets in less that an hour
Klingon font version? or go real retro and Sanskrit, Celtic Runes?

A quick google found one name of the engraving sheets.
https://www.gravograph.com.au/products- ... gravoply-2

[mahjongg]

I finished the BOM (Bill of materials) for building a single prototype.


almost all of it can be bought from Farnell, with a few parts coming from RS and Mouser.

more information can be found here: https://revspace.nl/Designing_the_RhoCo ... _materials

[Gavinmc42]

Sip7+ resistor arrays, I loved those when they came out, made DIY micro boards much neater

Also made things like a plug in fake eprom with NOP hardwired easier.
Plug one of those in and the micro would clock through the addresses.
Easy to test for address line shorts etc,
A cro would see square waves on each address line halving in frequency as you went up.

Only worked for those micros that start at 0x0000.

[mahjongg]

I remember the Motorola MC6800 (one of the very earliest 8-bit CPU's, the one predating most other 8-bit CPU's, except the i8080, and which "cheap copy" became the 6502) having a "halt and catch fire" instruction that simply halted execution, and continuously incremented the address counter. Handy for debugging the address decoder logic.

but no, the resistor network contains six, not eight, resistors, it's not meant for pulling up (or down) the databus (spectrum and ZX81 style to force NOP's on the bus).

[Gavinmc42]

You got me interested and I did a retro google.
I came into micros at that point, Hex display and keyboard on the MEK6800D2 kit.
Missed the point due to the expense of the 6800 but got hooked on 68HC05, 68HC11's a bit later.

Writing self modifying code on 6805's was fun.
6502 and Z80 survive but not many others.
Been wondering if a 6805 could be done in FPGAs?

Dug out manuals for the 6847 online, got an idea for a retro CRT look.
8x12 dot font, upper case only google for TT font or just make it?
A 32x16 terminal CRT would be handy for my OpenVG debugging.
Do Baudot instead of ASCII codes? Or is that too retro?

I never did get to a 6809 PC, the 6809 was supposed to be the best 8 bitter?
Instead I went into embedded jobs with 6805/11, not PC's.
PC's just became tools to write code for micros.
Until the Pi's.

[mahjongg]

I started assembling the prototype, for now I did the keyboard, and for the main board all the flatter components, up-to the height of the IC sockets.

This is how the partially assembled Rhococo looks like (from my Revspace wiki pages, where I document everything about rhococo) ;

[gordon77]

Looks very good.

[mahjongg]

thanks, will continue soon. you can read all about the progress, including many pictures, and an assembly description here: https://revspace.nl/Assembling_RhoCoCo

[scruss]

Lovely!

I spent the weekend nominally at the Midwest RepRap Festival, but really in the company of retro computer nerds. Josh was doing his S-100 Prototype Board stuff, Walter is deep in Superboard II country (building three from new boards, with keys harvested from a point-of-sale unit and key tops custom engraved) and I ended up going home with most of a Retro Elf

[davidcoton]

I still have a kit-built original UK101(Superboard II) -- no idea if it still works! Used as part of my final year degree project. Similar homemade wooden case to the one shown on Wikipedia.

[Heater]

mahjongg,

Did I ever mention here that I think your RhoCoCo is brilliant.

As you know I did create a CP/M running Z80 emulator on the Propeller + RAM + SD card. What I think I did not mention was that before I did that I also had the idea of building a machine with a real Z80 and a Propeller or two for the peripherals and terminal screen.

I would never have imagined taking it to the level you have with the RhoCoCo. It's looking really good.

[Gavinmc42]

Did I ever mention here that I think your RhoCoCo is brilliant.

Ditto, nearly had me looking for my Z84C00's, DIP Prop chips and some bread board.
Only got a bunch of 6116 SRAMs lying around
Nice trick with holding the Z80 in reset and loading the ram from the Prop.

Anyway you have provoked me into making something retro.
Done the Z80 stuff before the first time around, time to do something different.

Now have a bunch of A+ that are not used, never had "real" computing stuff, time for a VT100 console?
Back in the time of punch cards there where also a few colour terminals floating around Uni.
Never used them much, can barely recall what they looked like or were called.

Never use the UART on Pi's, time to play with that.

[mahjongg]

Finished the prototype, before plugging in any IC's I tried if powering it on worked, I have had bad experiences with trying to use an USB-B connector for power, previously I managed to reverse 5V and GND, but not this time.
The on-board power led turned on immediately when I switched rhococo on for the first time, and I had 5V and 3V3 on all the expected places, even after plugging in all IC's.

so here it is, turned on for the first time, with no "magic smoke" escaping:



the first test was keeping it on for a few minutes to see if anything got hot.... everything stayed quite cool.

Next week I can start trying to run code on the propeller chip.

I will start a new "bringing up rhococo" page.

[mahjongg]

Just for fun, and to show the ready prototype with keyboard lettering, here is a "family picture" of Rhococo with (some of) the (home)computers that inspired it.
on the background an MSX-2, a Sinclair Spectrum, a Raspberry PI, and a commodore 64, and on the foreground the prototype of Rhococo, without an enclosure.

[ejolson]

Just for fun, and to show the ready prototype with keyboard lettering, here is a "family picture" of Rhococo with (some of) the (home)computers that inspired it.
on the background an MSX-2, a Sinclair Spectrum, a Raspberry PI, and a commodore 64, and on the foreground the prototype of Rhococo, without an enclosure.

No Tandy CoCo? Looks nice though! Are periods and commas going to be control sequences involving the numeric keys?

[mahjongg]

I could have added the coco, but in fact it wasn't much of a consideration, given the limited graphics capabilities of an Motorola 6847 based system, it was never a popular choice for me. Also because it simply came out of the kitchen of Motorola, it was in fact, just like the dragon32, an only slightly modified demonstration board for Motorola's MC6847, (Microchroma 68 "TV bug" demonstrator board). Tandy only copied it, instead of developing something themselves, so they could rush something which did color to the marked.

In fact I liked the also MC6847 based Acorn Atom a little better, as it at least didn't simply copy Motorola's design.

So the "coco" part of rhococo is simply a coincidence. (sorry Coco fans)

And yes, the comma's and things like quotes and square brackets are extended inputs you reach with the Alt key.
All the normal signs like !@#$%^&*() you get with the shift like any normal keyboard, but because the inspiration of this keyboard came largely from the spectrum, with just a 8 extra keys in the matrix added to the Spectrums 40 Keys (4 rows of 10 keys) for a total of 48 keys (with three keys in parallel used for the space "bar", a grand total of 50 keys are used), I had to do some trickery to place all the common punctuation marks and such on the keyboard. Without the extra keys this keyboard is 100% spectrum compatible, it uses the same matrix and I/O interface.
The "new keys" are the four arrows and Ctrl keys, plus the three += backspace and |\ keys.

so to get the exclamation mark you just press shift 1 as normal but Alt 1 gives you Esc.
Similarly Shift 8 gives you an Asterix (*) but Alt 8 gives you a question mark (?) and Shift Alt 8 a slash (/).

Rhococo_keyboard.png (126.58 KiB) Viewed 7892 times

by the way, the Joystick will replicate the arrow keys, and the Ctrl button, so games can be played with either the keyboard or a normal Atari/MSX/C64 joystick.

[mahjongg]

A small update:
I found some hardware issues; Due to the ultra low quiescent current of both the propeller (PX32A) and the I/O expander chip, the chips powered with 3V3, and the fact that the Z80 injects some current from 5V into a GPIO through some current limiting resistors, the board, while still in full reset, had its 3V3 lifted up by the current through the PX32A's GPIO protection diode. So I added a 1mA bleeder resistor on the 3V3 to prevent this.
Similarly the diode in series with the SRAM power supply, did not manage to drop 0.7V when the SRAM chip was in standby, therefore I also used a bleeder resistor there, so I now have a stable 4.5V on the SRAM supply.
I noticed that all ceramic (foil) capacitors I bought had a 5mm wire pitch, while in my layout I use 2.5mm and 7.5mm pitches.
Then I found that the propeller chip would not come out of reset, and after some searching I found that I had the BOEn connected to 3V3, which disables the internal 5K pullup on RESETn in the propeller.
I changed some resistor values of resistors in series with propeller GPIO pins, and found one missing on IORQn. I patched my prototype, using "sockets" for the new resistor values, and patch resistors on the bottom of the PCB (it wasn't easy to patch BOEn to GND, so I opted for an external pullup instead, but I tried if it would work without the pullup, and with BOEn made low temporarily).
the picture below gives a closeup of of the patched resistors in "sockets".

closeup patches rhococ rev1,9.JPG (254.77 KiB) Viewed 7393 times

I saw that the (lightblue) patch resistors where slightly thicker than the dark blue regular 1/4 watt resistors, so much so that they didn't really fit next to each other, so I had to use two height levels. at least now I can experiment with the value of these series resistors, for now they are 15K.

I made a PCB redesign, version 2.0, where I addressed all these issues, I also separated the 8 data-line current limit resistors, so even a slightly thicker resistor will fit, and made all radial foil caps a 5mm pitch.

After finding the reason for the reset fault, I was able to use a small USB-serial dongle to connect rhococo to my laptop, and send a LED blink test program, and it worked, so I can upload programs to the PX32A, and store them in its EEPROM, so far so good. ITS ALIVE!

next up, getting a PX32A VGA driver program to work, so I have a video terminal to work with.

[scruss]

good use of machine-pin sockets there!
but what happened to that poor d-sub connector: burning? dremel? a dremel that caught fire?