Tiny SMD switches or tact switches for silly emulator project?

These are a bit smaller and easily available:

It would also be cool to use a stylus-operated membrane switch with the printed bit covering the whole top (windows for LEDs), and laminated to the PCB, but figuring out how to do that in a one-off without spending a fortune might be a hassle (it's not uncommon to have embedded SMT LEDs in a membrane kb/overlay). Also they woudn't be tactile most likely as there's litte room for a dome.

Best regards, Spehro Pefhany

Nice. I'll see if I can make this fit. Should just squeeze in.

I wanted to do this for a business card ZX Spectrum or ZX-81 emulator. Unfortunately, "due to other licensing arrangements" (cellphone ports of 8-bit games, I believe), Amstrad cannot license their firmware for this use.

If your stylus happens to be metal, a simple copper grid might suffice. A pair of interleaving comb patterns, with trace/space small enough so that the stylus will touch both adjacent traces without the tip radius bottoming out in the gap. Add an 0402 cap to debounce.

It's all the extra parts for ESD protection that I'd be worried about. The debounce wouldn be best done in firmware. Perhaps a stylus could be made with a softish* conductive rubber button at the end, but insulated from a plastic shaft. Maybe a zebra strip surgically modified-- cut to size and sliced horizontally to expose a conductive strip, then glued to squared-off end of an insulating rod.

Best regards, Spehro Pefhany

"Production" on this device might add up to 50 pieces, total. My BOM limit is about $60 per unit.

The smaller tacts Spehro pointed out look as if they might just work, I'm juggling stuff on the layout right now.

I will not be selling them. Hand-built units will be given away to select clients, colleagues and acquaintances. I guess if a DEC user group was interested, I'd give them one.

I _MAY_ make PCBs available for sale on my web site, and point to a Digi-Key BOM to populate it. However selling commercial goods in the United States is a terribly complicated thing to do; it's vast paperwork and pain and involves enormous sales tax forms for the seller. I'd rather have someone else make and sell them.

This is only the first one of several such projects I am working on (the others have ROM licensing problems that I'm working through, however). The other projects will have keyboards built in - the front will be a custom membrane keyboard (I'm not sure if I'm going to make it myself or buy it), and the back will be the electronics.

Well, that's because my limit is self-imposed; this is a fun personal project (which is more or less entirely deductible as a promotional expense). That limit is _really_ easy to reach, by the way - the micro alone is $12, and in the quantities I will buy them, the switches will be $30-odd. I think I'll get Olimex to do the PCBs.

BTW, at work I would be a company hero (probably rating a mention in the worldwide monthly newsletter) if I could save $1.00 on the highest-volume project for which I'm responsible.

Good tip, thanks. The wings tend to stick up and down rather than side to side, which is good because I have plenty of vertical room but not much horizontal.

These are a wee bit smaller but not by much:

Digikey has them but they are expensive if this is for a production run. Spehro's idea regarding rubber contact areas sounds good. If this is a one off demo prject you might be able to cut something from an old remote pad.

Regards, Joerg

Hello ZWS,

That's a pretty cushy BOM limit. Drool. Mine right now is $7 including assembly and test. But higher qties.

If you can afford the space look for gull wing parts. They take a beating better than J-lead, in my experience. Especially if the card might be flexed a bit.

Regards, Joerg

I'll buy one if the selling price is reasonable.. say, $100. Looks really neat. Nerdy and wierd. I like it!

I said "a" user group, not "every" user group :P

Hey, if you have the infrastructure to sell these things, go ahead with my blessing; make 'em, sell 'em, profit enormously, give me no money - as long as you leave my name and URL on the board.

If, in fact, you have "plenty of vertical room", then I'd strongly recommend toggle-handle DIP switches, maybe with a little switch clicker stylus thingie on a lanyard. They'd be much more like the front panel I saw in that image somewhere, which had actual toggle switches.

And if they're to be handed out as a promo, the switch lifetime issues shouldn't come up, but if that's _really_ a worry, then a low- profile dip switch in a low-profile socket might fit the bill. :-)

I wonder how many of Guy Macon's BCD R-C substitution boxes are in the field, and how they're holding up? ;-)

Good Luck! Rich

Hello Lewin,

So, folks, start a DEC user group quickly...

Sad. That appears to be one reason that is impeding progress in our country. Things need to be made simpler, big time.

Regards, Joerg

No worries. I can upload the ZX Spectrum ROM myself. Will it have video-out and a microdrive (or SD/MMC card)? ;-)

It's a worthless project to me if it is not plug-n-play though.

Amstrad said, and I quote almost verbatim, "due to other business arrangements we are no longer able to give our permission to distribute our copyrighted material". This was carefully worded, I think - note that he didn't say "and we will pursue violators to the ends of the earth and wreak vengeance unto the seventh generation".

The "other business arrangements", if I recall my news stories correctly, consist of Amstrad licensing its 8-bit micro intellectual property en masse to somebody developing games for cellphones.

I'm not sure how to handle the video on the Spectrum.

Yes, good point. Their Sinclair ROM's including documented assembler have been out there for soo long now that I am surprised that they bother. But as soon as lawyers get involved... ;-)

You'd need a second processor that uses the Z80 instruction cycles to read RAM and generate the image. Kind of interleaving Z80 vs. video processor access. That's why all those early homecomputers up to the Amiga had so funny clocks like 3.6MHz or 7.16MHz .... .

How about a PDA like [transparent] sensor over your card?

Actually interleaving CPU accesses with video accesses started with the Apple II [Ca 1972] and most any related patent is expired.

My kids are reaching the age where they are ready to start learning about the fiddly little bits inside a computer, and some recent talk of the switches-and-lights computers has me interested in getting such a thing.

Does anyone make a commercially-available (real or emulated) processor with switches and lights like we all learned on in The Good Old Days?

I've found

Thanks!