Tiny SMD switches or tact switches for silly emulator project?

[[email protected]]

Tried this in comp.arch.embedded, moving my search further afield...

I'm trying to build a PDP-1 emulator on a 90x55mm business card. As
readers skilled in the art will appreciate, this is an eminently
practical project, the general applicability and consumer utility of
which are precisely commensurate with the profits I expect to realize
from the endeavor.

The front side of the card contains the front panel. 0603 LEDs for the
lamps are fine, but I am having trouble finding switches small enough.
Smallest tact switches I can find are 6x3mm. Can anyone point me to
smaller tact switches? My other option is 0.050" spacing DIP switches,
which are harder to operate and have a shorter lifespan.

An old photo of the original:

http://www.dbit.com/~greeng3/pdp1/PDP1.10.jpg

my current mechanical test layout (missing address and test word
switches):

http://www.larwe.com/pdpcard.gif

and a 1:1 scale printout of the layout in my hand:

http://www.larwe.com/PDRM1836.JPG

(As with the real computer, the electronics and power supply are behind
the front panel. The emulator is implemented in a 60MHz ARM7).

 

[Mike Harrison]

Tried this in comp.arch.embedded, moving my search further afield...

I'm trying to build a PDP-1 emulator on a 90x55mm business card. As
readers skilled in the art will appreciate, this is an eminently
practical project, the general applicability and consumer utility of
which are precisely commensurate with the profits I expect to realize
from the endeavor.

The front side of the card contains the front panel. 0603 LEDs for the
lamps are fine, but I am having trouble finding switches small enough.
Smallest tact switches I can find are 6x3mm. Can anyone point me to
smaller tact switches? My other option is 0.050" spacing DIP switches,
which are harder to operate and have a shorter lifespan.

Omron do some 4mm dia. domes (B3D-4112).
ITT Cannon do a side-actuated one with a 1.66x3.5mm profile x 5.5mm wide - if you could find a way
to stack these maybe they would be worth a look. KSS221G

Also look at people like ALPS, but obtaining small qtys may be tricky. Perhaps investigate dead
digital cameras/mobile phones....

 

[Mike Harrison]

Tried this in comp.arch.embedded, moving my search further afield...

I'm trying to build a PDP-1 emulator on a 90x55mm business card. As
readers skilled in the art will appreciate, this is an eminently
practical project, the general applicability and consumer utility of
which are precisely commensurate with the profits I expect to realize
from the endeavor.

The front side of the card contains the front panel. 0603 LEDs for the
lamps are fine, but I am having trouble finding switches small enough.
Smallest tact switches I can find are 6x3mm. Can anyone point me to
smaller tact switches? My other option is 0.050" spacing DIP switches,
which are harder to operate and have a shorter lifespan.

An old photo of the original:

http://www.dbit.com/~greeng3/pdp1/PDP1.10.jpg

my current mechanical test layout (missing address and test word
switches):

http://www.larwe.com/pdpcard.gif

and a 1:1 scale printout of the layout in my hand:

http://www.larwe.com/PDRM1836.JPG

(As with the real computer, the electronics and power supply are behind
the front panel. The emulator is implemented in a 60MHz ARM7).

As the device is likely to be hand-held, how about using pcb touch pads, in conjunction with a
conductive stylus (grounded via the users body where they old it).
A PCB pad with a LED next to it would get the size down significantly. Probably wouldn't need any
extra circuitry - just some 1M or so pullups, maybe a couple of diodes and a series resistor for ESD
protection.

 

[Spehro Pefhany]

Tried this in comp.arch.embedded, moving my search further afield...

I'm trying to build a PDP-1 emulator on a 90x55mm business card. As
readers skilled in the art will appreciate, this is an eminently
practical project, the general applicability and consumer utility of
which are precisely commensurate with the profits I expect to realize
from the endeavor.

The front side of the card contains the front panel. 0603 LEDs for the
lamps are fine, but I am having trouble finding switches small enough.
Smallest tact switches I can find are 6x3mm. Can anyone point me to
smaller tact switches? My other option is 0.050" spacing DIP switches,
which are harder to operate and have a shorter lifespan.

An old photo of the original:

http://www.dbit.com/~greeng3/pdp1/PDP1.10.jpg

my current mechanical test layout (missing address and test word
switches):

http://www.larwe.com/pdpcard.gif

and a 1:1 scale printout of the layout in my hand:

http://www.larwe.com/PDRM1836.JPG

(As with the real computer, the electronics and power supply are behind
the front panel. The emulator is implemented in a 60MHz ARM7).

These are a bit smaller and easily available:
http://www3.alps.co.jp/WebObjects/catalog.woa/PDF/E/Switch/Tact/SKRK/SKRK.PDF

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

 

[Mike Harrison]

These are a bit smaller and easily available:
http://www3.alps.co.jp/WebObjects/catalog.woa/PDF/E/Switch/Tact/SKRK/SKRK.PDF

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.

You could use a sounder click to provide pseudo-tactile feedback.

 

[Spehro Pefhany]

You could use a sounder click to provide pseudo-tactile feedback.

Might even be tactile rather than auditory if you could whack the
board hard enough. ;-)


Best regards,
Spehro Pefhany

 

[[email protected]]

These are a bit smaller and easily available:
http://www3.alps.co.jp/WebObjects/catalog.woa/PDF/E/Switch/Tact/SKRK/SKRK.PDF

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

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

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.

 

[DJ Delorie]

It would also be cool to use a stylus-operated membrane switch with

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.

 

[Spehro Pefhany]

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.

*whatever durometer that turns out to be


Best regards,
Spehro Pefhany

 

[Joerg]

Smallest tact switches I can find are 6x3mm. Can anyone point me to
smaller tact switches? My other option is 0.050" spacing DIP switches,
which are harder to operate and have a shorter lifespan.

These are a wee bit smaller but not by much:
http://www.panasonic.com/industrial/components/pdf/atk0000ce6.pdf

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

 

[[email protected]]

These are a wee bit smaller but not by much:
http://www.panasonic.com/industrial/components/pdf/atk0000ce6.pdf

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.

"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.

 

[Joerg]

Hello ZWS,

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

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

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

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

 

[carl0s]

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

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

 

[[email protected]]

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

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.

 

[[email protected]]

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

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.

If you can afford the space look for gull wing parts. They take a

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.

 

[Joerg]

Hello Lewin,

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.

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

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. ...

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

Regards, Joerg

 

[[email protected]]

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

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

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

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.

 

[Rich Grise]

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.

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

 

[Matthias Melcher]

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).

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

 

[[email protected]]

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.