Touchpads
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Posts: 46,084
Hi stampers,
is there anyone out there who knows how to connect a simple metal plate to a
stamp and make the stamp recognize whenever someone touches it?
I have a solution right here but Mike says static voltage is gonna kill it
and I guess he might be right. (I just pull up the stamp input with 1 meg
ohm and then if you touch it it starts flickering between low and high and I
detect this by a count command).
Any suggestions? Doesnot have to be dead cheap because I am doing this for a
company, they pay! :-)
Thanks for suggestions,
Uli
[noparse][[/noparse]Non-text portions of this message have been removed]
is there anyone out there who knows how to connect a simple metal plate to a
stamp and make the stamp recognize whenever someone touches it?
I have a solution right here but Mike says static voltage is gonna kill it
and I guess he might be right. (I just pull up the stamp input with 1 meg
ohm and then if you touch it it starts flickering between low and high and I
detect this by a count command).
Any suggestions? Doesnot have to be dead cheap because I am doing this for a
company, they pay! :-)
Thanks for suggestions,
Uli
[noparse][[/noparse]Non-text portions of this message have been removed]
Comments
Kevin
ulibasic wrote:
>
> Hi stampers,
>
> is there anyone out there who knows how to connect a simple metal plate to a
> stamp and make the stamp recognize whenever someone touches it?
> I have a solution right here but Mike says static voltage is gonna kill it
> and I guess he might be right. (I just pull up the stamp input with 1 meg
> ohm and then if you touch it it starts flickering between low and high and I
> detect this by a count command).
> Any suggestions? Doesnot have to be dead cheap because I am doing this for a
> company, they pay! :-)
>
> Thanks for suggestions,
>
> Uli
>
> [noparse][[/noparse]Non-text portions of this message have been removed]
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
simply connect the input to 2 fast diodes as below.
Then the input voltage can never exceed Vss -0.7V or
Vdd +0.7V wich are safe for the BS.
Vdd |
-
^
|
In
|
-
^
|
Vdd
Regards
ECO
Original Message
From: "ulibasic" <ulibasic@r...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, September 21, 2001 9:53 AM
Subject: [noparse][[/noparse]basicstamps] Touchpads
> Hi stampers,
>
> is there anyone out there who knows how to connect a simple metal plate to a
> stamp and make the stamp recognize whenever someone touches it?
> I have a solution right here but Mike says static voltage is gonna kill it
> and I guess he might be right. (I just pull up the stamp input with 1 meg
> ohm and then if you touch it it starts flickering between low and high and I
> detect this by a count command).
> Any suggestions? Doesnot have to be dead cheap because I am doing this for a
> company, they pay! :-)
>
> Thanks for suggestions,
>
> Uli
>
>is there anyone out there who knows how to connect a simple metal plate to a
>stamp and make the stamp recognize whenever someone touches it?
>I have a solution right here but Mike says static voltage is gonna kill it
>and I guess he might be right. (I just pull up the stamp input with 1 meg
>ohm and then if you touch it it starts flickering between low and high and I
>detect this by a count command).
>Any suggestions? Doesnot have to be dead cheap because I am doing this for a
>company, they pay! :-)
>
>Thanks for suggestions,
>
>Uli
Hi Uli,
The solution you have there depends on having a fairly strong 60hz
electromagnetic field in the vicinity of the chip. Are you sure that
your customer can count on that? Say you take this from your office
out to some rural location, the fields will not be so strong. Or if
it gets installed under a high tension line, the fields might trigger
your circuit without a finger touching it. Another possible concern
is that of having a person directly touch a metal plate, if there
could be any possiblility of a fault in the equipment causing harm to
the person.
That said, the 60hz pickup idea could work with a high ohm value
resistor in series with the pin to protect it from static, and to
protect the person from shock too. I think you said you are using
100 ohms now. You could bump that up to 100 kohms, to limit current
to the PICs protection diodes.
|
+5---/\/\----o----/\/\----| plate
10 Mohm | 100kohm |
sensitivity |
|
p0 on Stamp
The chips from qprox <http://www.qprox.com> depend on capacitance
changes, not on 60hz pickup. They are very easy to use, and even
allow an insulating layer between the metal plate and the finger
touching it.
-- regards,
Tracy Allen
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com
ever worked with...Mike's on the money...
CL
>
Original Message
> From: ECO [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=tylsChQGPNOjzjlwZ4ggIhBAgq6PMycN7qOi6X9v9WoUVdxnTfwP0e3a16c4UAmfMbzCeZTB_cx2ZKQ]ecourt@b...[/url
> Sent: Friday, September 21, 2001 10:21 AM
> To: basicstamps@yahoogroups.com
> Subject: Re: [noparse][[/noparse]basicstamps] Touchpads
>
>
> Uli
> simply connect the input to 2 fast diodes as below.
> Then the input voltage can never exceed Vss -0.7V or
> Vdd +0.7V wich are safe for the BS.
>
Vdd |
> -
> ^
> |
>
In
> |
> -
> ^
> |
>
Vdd
>
> Regards
> ECO
>
> ----
Original Message
> From: Chris Loiacono [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=v15khoRd1q8C_-HxIXk0bZESzgrh6a-7wYPoXNFmolzOFqkEcNzZxE4cwFWL3BgCFUkfNo_oJ8ZT6w]chris@m...[/urlOn Behalf Of
> chris@t...
> Sent: Friday, September 21, 2001 9:43 AM
> To: 'basicstamps@yahoogroups.com'
> Subject: RE: [noparse][[/noparse]basicstamps] Touchpads
>
>
> Uli:
>
> If you already have a solution for this, great. If not, about
> 25 years ago I made a simple touch switch based on a small
> Darlington pair that was nearly indestructible. Today I would
> use opto's to keep the input pins and people touching the switches safe.
Your input model may
> suffice if it is isolated from the stamp as well (to be
> honest, I didn't read all the previous messages on this
> subject). I'm stuck on optically isolating inputs and outputs
> as a habit (I guess it comes from working with uC's and AC so
> often) that isolating your input scheme from the stamp pins
> may let you sleep. If you want to really isolate it, you may
> think about using a second supply for the inputs, this way,
> only the optoisolator output is on the same ground as the
> stamp. Just say so and I will attempt to dig up something on
> the Darlington touch switch. There are many, many choices in
> opto chips, from single to 4-up types. I would think almost
> any with transistor output will do. I think I would use a
> second fast diode across (inversely parallel to) each opto's
> LED to protect against reverse voltage spikes - that's the
> one thing that can hurt the opto's LED's.
>
> Chris
>
> >
Original Message
> > From: ulibasic [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=qH4JjLqVUfo2POLDnWq7TooOpRpxjxtKk4ROiDpEn5SU0_6O3TX7U9xWncSFoA_wTw5ffbM4d7GgseCYVzA1Pzaot1ObKwuN]ulibasic@r...[/url
> > Sent: Friday, September 21, 2001 3:54 AM
> > To: basicstamps@yahoogroups.com
> > Subject: [noparse][[/noparse]basicstamps] Touchpads
> >
> >
> > Hi stampers,
> >
> > is there anyone out there who knows how to connect a simple
> > metal plate to a
> > stamp and make the stamp recognize whenever someone touches it?
> > I have a solution right here but Mike says static voltage is
> > gonna kill it
> > and I guess he might be right. (I just pull up the stamp
> > input with 1 meg
> > ohm and then if you touch it it starts flickering between low
> > and high and I
> > detect this by a count command).
> > Any suggestions? Doesnot have to be dead cheap because I am
> > doing this for a
> > company, they pay! :-)
> >
> > Thanks for suggestions,
> >
> > Uli
> >
> >
> >
> >
> >
> > [noparse][[/noparse]Non-text portions of this message have been removed]
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
> > Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
> >
>
My original comments about ESD protection networks probably aren't too far
off target, but you could simplify things a bit by using Schottky
protection diode arrays such as Zetex' SDAxx series, connected as above,
and eliminating the downstream resistor. I think Motorola (On?) and Micrel
make similar components, and they might offer app notes that would help you.
One of the functions of the input side resistor is to help limit the rise
time of incoming voltage spikes, so the diode has time to start conducting.
This function, as well as its current-limiting function, is defeated if the
resistor arcs internally. That's why it's important to limit applied
voltage somehow (perhaps a spark gap designed into the PCB artwork), and
size that resistor to take the punishment.
>Not necessarily so. ESD events are much faster than any 'fast ' diode I've
>ever worked with...Mike's on the money...
>> simply connect the input to 2 fast diodes as below.
>> Then the input voltage can never exceed Vss -0.7V or
>> Vdd +0.7V wich are safe for the BS.
>>
Vdd |
>> -
>> ^
>> |
>>
In
>> |
>> -
>> ^
>> |
>>
Vdd
Mike Hardwick, for Decade Engineering -- <http://www.decadenet.com>
Manufacturer of the famous BOB-II Serial Video Text Display Module!
check out the QProx website (www.qprox.com). They sell a variety of
touch sensors that can be easily interfaced with the basic stamp, or
used as stand-alone devices.
Good luck,
peter