Maker Pro
Maker Pro

Homebrew membrane keypad

D

Dmitri

Jan 1, 1970
0
Hello everyone!

It looks like homebrew PCBs are a pretty well developed branch of the
electronics hobby these days, even I have (more or less successfully) made
them. How about membrane keyboards?
I'm looking for some info on whether or not anyone has attempted to make
membrane keyboards in a garage workshop environment. What materials may be
required? Anything that can be available to a non-pro?
I have a project that requires eight buttons under an LCD, and a membrane
keyboard would work extremely nice, especially if I can conceal the gutts
of the scheme beneath it. it would go on top of a plastic project box.

Any link, suggestion, info anyone?

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------



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S

Spehro Pefhany

Jan 1, 1970
0
Hello everyone!

It looks like homebrew PCBs are a pretty well developed branch of the
electronics hobby these days, even I have (more or less successfully) made
them. How about membrane keyboards?
I'm looking for some info on whether or not anyone has attempted to make
membrane keyboards in a garage workshop environment. What materials may be
required? Anything that can be available to a non-pro?
I have a project that requires eight buttons under an LCD, and a membrane
keyboard would work extremely nice, especially if I can conceal the gutts
of the scheme beneath it. it would go on top of a plastic project box.

Any link, suggestion, info anyone?

You can make a graphic overlay and put tact switches behind it. Many
high volume consumer appliances are made that way, while others have
custom-molded operators that work tact switches.


Best regards,
Spehro Pefhany
 
R

Roger Lascelles

Jan 1, 1970
0
Dmitri(Cabling-Design.com) said:
Hello everyone!

It looks like homebrew PCBs are a pretty well developed branch of the
electronics hobby these days, even I have (more or less successfully) made
them. How about membrane keyboards?
I'm looking for some info on whether or not anyone has attempted to make
membrane keyboards in a garage workshop environment. What materials may be
required? Anything that can be available to a non-pro?
I have a project that requires eight buttons under an LCD, and a membrane
keyboard would work extremely nice, especially if I can conceal the gutts
of the scheme beneath it. it would go on top of a plastic project box.

Any link, suggestion, info anyone?

Membrane keypads have silver or carbon tracks on a sheet of film - the
tracks expand to form switch contacts and form a film ribbon cable for the
external connection. A switch consists of a metal dome which gives way
suddenly when pressed, giving tactile feedback and completing the contact.
The domes are put in place and the whole thing stuck together - as 3 layers
of plastic. The process is critical - we got a lot of bad switches due to
silver migration, ribbon carbon tracks cracking, contact trouble, bad domes.

From my experience with membrane switches I will try to avoid them, even for
commercial products. The simple, quality alternative is a label with TACT
switches. Drill say 12 mm holes in the panel at each switch position, and
stick the label on top. The PCB with TACT switches sits underneath, with the
switch tops just touching the label. I know someone who produced broadcast
consoles that way, with a big sheet of lexan over the entire area of the
desk. You can get bigger TACT switches too, for a better feel. Has
advantage that you can pull PCB out of case and switches are still on the
PCB. If you find your switches are not close enough to label, put shiny
paper stickers over switch buttons and stick blobs of silastic on label,
just above switches. Put it all together for 12 hours and when you take it
apart, the blobs will stay on the label. Commercially printed Lexan is
expensive, so the hobbiest bit might be to find a nice tough label you can
print with a laser printer. Might want to stick a sheet of clear over the
laser printing ?

Roger
 
N

Nicholas O. Lindan

Jan 1, 1970
0
Dmitri(Cabling-Design.com) said:
I'm looking for some info on whether or not anyone has attempted to make
membrane keyboards in a garage workshop environment.

Usenet rule #12a: The answer to 'has anyone else...?' is 'yes'.
However, that does not mean it is a good thing to do. A DIY
membrane keyboard sounds like a lot of time and money for
a really bad keyboard.
I have a project that requires eight buttons under an LCD

Use a set of 8 real switches:

http://www.cherrycorp.com/english/switches/key/mx.htm

digikey etc.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Roger Lascelles
Commercially printed Lexan is expensive, so the
hobbiest bit might be to find a nice tough label you can print with a
laser printer. Might want to stick a sheet of clear over the laser
printing ?

Print in reverse on the lower side ('second-surface printing'). OHP film
works.
 
S

Spehro Pefhany

Jan 1, 1970
0
I read in sci.electronics.design that Roger Lascelles


Print in reverse on the lower side ('second-surface printing'). OHP film
works.

Only a very few inkjet (and maybe no laser) printers will print opaque
white. The colors are also quite transparent. I use screening methods,
but it involves some investment for materials and equipment, costs
money for each design (for screen and die(s)), and is very
messy/smelly.

Here's an example: http://www.speff.com/tachs.jpg



Best regards,
Spehro Pefhany
 
C

ChrisGibboGibson

Jan 1, 1970
0
Spehro said:
Only a very few inkjet (and maybe no laser) printers will print opaque
white. The colors are also quite transparent. I use screening methods,
but it involves some investment for materials and equipment, costs
money for each design (for screen and die(s)), and is very
messy/smelly.

Here's an example: http://www.speff.com/tachs.jpg

I've had good results for prototypes printing on the reverse of OHP film using
3 colour plus black ink jet then spraying the remainder white. That way you can
have any colour you want. It's then glued using aerosol glue.

Gibbo
 
S

Spehro Pefhany

Jan 1, 1970
0
I've had good results for prototypes printing on the reverse of OHP film using
3 colour plus black ink jet then spraying the remainder white. That way you can
have any colour you want. It's then glued using aerosol glue.

Gibbo

I have a client who does that except with yellow spray on the back,
and punched on a little press. Pretty labor-intensive, but the results
look very professional unless you look very closely. He uses a special
professional film available only in huge rolls or sheets.

With screen techniques, I can pick any thickness or surface finish
(pebble or hardcoat or plain) of polycarbonate or polyester film I can
get ahold of, print transparent colors or opaque and so on. I use a
vinyl type ink compatible with both polycarbonate and polyester. UV
curing would be a somewhat more pleasant process to work with, but the
cost of the inks and equipment would be much higher.


Best regards,
Spehro Pefhany
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Spehro Pefhany <speffSNIP@interlog
Only a very few inkjet (and maybe no laser) printers will print opaque
white. The colors are also quite transparent.

Naturally; for OHP they wouldn't work if opaque!
I use screening methods,
but it involves some investment for materials and equipment, costs money
for each design (for screen and die(s)), and is very messy/smelly.

I print only the legends and use a coloured paper or plastic sheet for
the background colour.
 
J

John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that ChrisGibboGibson
I've had good results for prototypes printing on the reverse of OHP film
using 3 colour plus black ink jet then spraying the remainder white.
That way you can have any colour you want. It's then glued using aerosol
glue.

I've done that, too, but of course it doesn't work with inkjet printing
because the spray solvent re-dissolves the ink. For black legends only,
a photocopy works.
 
K

Ken Smith

Jan 1, 1970
0
Hello everyone!

It looks like homebrew PCBs are a pretty well developed branch of the
electronics hobby these days, even I have (more or less successfully) made
them. How about membrane keyboards?

I knew someone who did it. I won't say it is a good idea but here's what
he did:

There was a PCB layout where each button was a interdigitated pattern like
this:



------------- The trace width and spacing was the
! -------------! finest he could do with the tape on
!------------ ! copper clad etching method
! -------------!

... etc ..


I think he had one of those "plating pens" that hook up to a battery. I
don't know for a fact how he plated the pattern but it was shiny when I
saw it. Both sides of each switch pattern was connected to traces that
went out past the edge of the keyboard area.

Over this PCB he placed a sheet of Mylar with about 1CM diameter holes
where the buttons were. He used the 3M "transfer film" to stick the Mylar
in place.

Over this he stuck the metalized plastic film that was used in
electro-static speakers. I think it was nickle on Mylar.

At one time 3M made this film that was intended for front panels etc. It
used a photographic process. You had to tape up the pattern you wanted on
some Mylar and run the sheets through a blue print machine. This was then
wided down with developer and then dryed and sprayed with mat finish
Krylon.


He reported that the resulting keypad worked well. I think however that
he spent more time on making it than it really was worth.
 
K

Ken Smith

Jan 1, 1970
0
I read in sci.electronics.design that ChrisGibboGibson


I've done that, too, but of course it doesn't work with inkjet printing
because the spray solvent re-dissolves the ink. For black legends only,
a photocopy works.

I'll suggest the 3M transfer stuff or a sheet of sticky backed Mylar to
stick to it without disolving the ink.
 
S

Spehro Pefhany

Jan 1, 1970
0
I read in sci.electronics.design that ChrisGibboGibson


I've done that, too, but of course it doesn't work with inkjet printing
because the spray solvent re-dissolves the ink.

Maybe if you Krylon the ink before spraying the background, or
experiment with different paints. The inkjet stuff seems to be
water-based and the spray paints generally have petroleum type
solvents. Oil and water.
For black legends only, a photocopy works.

I've seen ads from a company in Quebec who will prototype overlays for
about $400 US (before the dollar plummeted, so maybe $500 now). This
is still a ways above proto prices for PCBs.


Best regards,
Spehro Pefhany
 
C

ChrisGibboGibson

Jan 1, 1970
0
John said:
I read in sci.electronics.design that ChrisGibboGibson


I've done that, too, but of course it doesn't work with inkjet printing
because the spray solvent re-dissolves the ink. For black legends only,
a photocopy works.

Cellulose spray destroys the actual substrate, water based (quite common now
for cars, especially 2 pack) destroys the ink, 1 pack polyeurethane works fine
with normal ink jet cartridges.

Gibbo
 
G

Guy Macon

Jan 1, 1970
0
Spehro said:
Only a very few inkjet (and maybe no laser) printers will print opaque
white. The colors are also quite transparent. I use screening methods,
but it involves some investment for materials and equipment, costs
money for each design (for screen and die(s)), and is very
messy/smelly.

So is Rich, but we still like him... :)
 
J

john jardine

Jan 1, 1970
0
ChrisGibboGibson said:
I've had good results for prototypes printing on the reverse of OHP film using
3 colour plus black ink jet then spraying the remainder white. That way you can
have any colour you want. It's then glued using aerosol glue.

Gibbo

I've used the OHP film. Reverse printed Black, sprayed with art-mount glue
and some metallic foil stuck on to show thru the clear bits. (that thin,
red/blue/gold/silver etc, mirror finish stuff for wrapping Christmas
presents.
regards
john
 
R

Rich Grise

Jan 1, 1970
0
Hello everyone!

It looks like homebrew PCBs are a pretty well developed branch of the
electronics hobby these days, even I have (more or less successfully) made
them. How about membrane keyboards?
I'm looking for some info on whether or not anyone has attempted to make
membrane keyboards in a garage workshop environment. What materials may be
required? Anything that can be available to a non-pro?
I have a project that requires eight buttons under an LCD, and a membrane
keyboard would work extremely nice, especially if I can conceal the gutts
of the scheme beneath it. it would go on top of a plastic project box.

Any link, suggestion, info anyone?

Have you ever taken apart a PC keyboard? If you can connect to the traces,
(probably with some kind of clip - I haven't tried to solder to one), you
could just use the plastic membrane switch thing from one of them. Or make
something in the same style.
http://rich_grise.tripod.com/images/Keyboard1.jpg

Good Luck!
Rich
 
D

Dmitri

Jan 1, 1970
0
Spehro Pefhany wrote:

Only a very few inkjet (and maybe no laser) printers will print opaque
white. The colors are also quite transparent. I use screening methods,
but it involves some investment for materials and equipment, costs
money for each design (for screen and die(s)), and is very
messy/smelly.
Here's an example: http://www.speff.com/tachs.jpg


Best regards,
Spehro Pefhany

Man, the panel looks awesome! I understand that it is on a flat surface,
so it is not exactly the same as the keyboard-type setup I'm after, but it
is certainly the way to go. Would you mind giving more details about the
equipment for the screening?

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------





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D

Dmitri

Jan 1, 1970
0
Ken said:
There was a PCB layout where each button was a interdigitated pattern
like
this:
------------- The trace width and spacing was the
! -------------! finest he could do with the tape on
!------------ ! copper clad etching method
! -------------!
... etc ..

Thanks for the info, Ken!

I was thinking along the same lines, glad to see that some brave soul has
already gone through it ;-).

There are couple critical points here as far as I can tell. Well, as
usual, you find more and more critical points as you go deep into it, but
these two seem obvious for me now:

1. The pattern needs to be silver plated to prevent oxidizing, and I'm not
sure about details of the process.
2. The conductive film that would go on top of the Mylar sheet is a
mystery for me, have no idea where to get it. On the other hand, it only
needs a small patch of conductive material to overlap couple of those
traces, so maybe a small round piece of (silver plated?) copper peeled off
a PCB will do.
He reported that the resulting keypad worked well. I think however
that
he spent more time on making it than it really was worth.

The entire thing about this hobby is to ejoy time doing it, so it does not
really matter how long it takes, as long as the result is achievable.

I am, however, leaning toward putting a tactile switches behind a legend,
printed on transparency as suggested by other posters here. It seems like
the actual electrical contact, which is a heart of the keyboard is going
to be unreliable, which would defeat the whole purpose of making it. I
just have to figure out the white background for spaces, not printed by my
color laser printer.

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------

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D

Dmitri

Jan 1, 1970
0
I wanted to thank everyone responded to my message. I now realize that the
problem is a bit more complex than I originally thought, although I may
attempt to make a model in the future. For now on, I would rather take
Spehro's and Roger's suggestion and put a tact switches behind a printed
legend. I think, in my case, it will have to be two layers - one laser
printed transparency (with holes punched above the switches) to cover the
LCD and another printed on a sticky 1" tape by a Brother P-Touch graphic
label printer I have. P-Touch does not have the problem of transparent
spots where white was intended as it has its own background color, and you
get to choose one. Besides, it has a very uniform and sticky adhesive
later on the bottom, and is very widely available (though not too cheap ;-)

While researching for the membrane keyboards, found this nice resource
with lots of illustrations and other useful info:
http://www.membraneswitchtech.com/layers.htm
Check it out, my be useful to somebody who's into homebrew keyboards.

--
Dmitri Abaimov, RCDD
http://www.cabling-design.com
Cabling Forum, color codes, pinouts and other useful resources for
premises cabling users and pros
http://www.cabling-design.com/homecabling
Residential Cabling Guide
-------------------------------------


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