Searching \ for '[EE] Touch swtich options for automotive-based PIC' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/microchip/devices.htm?key=pic
Search entire site for: 'Touch swtich options for automotive-based PIC'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Touch swtich options for automotive-based PIC'
2008\01\18@184911 by picdude2

flavicon
face
Hi all,

I want to replace a tact-switch in an automotive PIC application with some type
of touch-switch, and wondering what options exist.  Currently that application
has an acrylic front, which has a small hole for the stem of the tact switch
(plus some LED displays etc on the inside).  The touch switch would need to be
small and low cost.  I don't expect it to be $0.10 as the tact switch is, but I
figure up to $1 would be nice (in quantity).  Also, PCB-space is limited, so it
needs to be not much larger than a 6mm x 6mm tact switch.  Say 10mm x 10mm would
be acceptable.

In my basic investigation so far (quite some time ago), I found specialized chips
that are a bit pricey and larger (such as Q-Prox), so I'm looking for some other
option or other technology, such as a discrete circuit option.  I'm envisioning
being able to do this with a spare PIC I/O (or two?) and some minimal protection
circuitry to that I/O pin.  Capactive, light-sensing, etc would be fine.

Any thoughts, pointers, etc?

Cheers,
-Neil.




2008\01\18@203806 by Dwayne Reid

flavicon
face
At 04:48 PM 1/18/2008, spam_OUTpicdude2TakeThisOuTspamavn-tech.com wrote:
>Hi all,
>
>I want to replace a tact-switch in an automotive PIC application
>with some type
>of touch-switch, and wondering what options exist.  Also, PCB-space
>is limited, so it
>needs to be not much larger than a 6mm x 6mm tact switch.  Say 10mm
>x 10mm would
>be acceptable.

My favorite is still the old cmos 555 timer in soic8.  My touch
switches use a single tlc555 or similar per touch pad: pins 2 & 6
tied together, then to a 10K resistor, other side of resistor is back
side surface of touch pad.  Pin 3 has 470K resistor also connected to
back side surface of touch pad; pin 3 feeds PIC.  Pin 1 is gnd, pin 8
is Vdd, pin 4 is either tied HI (timer runs continuously) or is gated.

Top side pad is floating - not connected to anything.  It is
capacitively coupled to the bottom side pad.

I gate each touch switch in turn if there is more than 1: all of the
output pins (pin 3) are diode-coupled into the clock buss.  Most of
my touch pads have LEDs associated with them - the LED sticks through
a hole in the PCB and either illuminates the covering label or shines
through a hole in the label.

Most of my touch pads are fairly large - about 0.5" square or 0.6"
square.  I leave about 0.075" space around each top-side pad between
the pads and the ground plane that otherwise covers the top side of the PCB.

I picked the feedback resistor (470K) such that the free-running
period was about 6us.  That increases to about 12us when the top pad
is touched.  The reasons are as follows:

The shortest (2 instruction) delay loop (PIC 12 bit or 14 bit core)
takes 767 cycles to execute (255*3 +2).  I used that as a timebase to
accumulate pulses into TMR0 via its external clock input.  TMR0 will
wrap if the pulse period drops below about 3us: choosing 6us minimum
period gives lots of leeway even with normal manufacturing tolerances.

TMR0 result for each pad is averaged by 2 different filters: a 256
times filter (long term average) and a short 8 times filter.  Touch
is detected when there is a significant difference between the filtered values.

This results in an extremely robust and reliable touch switch that
self-tunes to changes in operating conditions.

Not a single switch has failed in use due to ESD or any other
external event other than physical damage (smashed with a
hammer).  The main reason for that reliability, of course, is the
extremely high breakdown voltage of the FR4 substrate that separates
the top and bottom touch pads.  The series resistors connecting the
bottom surface of the touch pad to the TLC555 are also an important
part of the ESD reliability.

FWIW - the TLC555 is about $0.30 in small to medium quantities.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam@spam@planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2008\01\18@205324 by Jinx

face picon face
part 1 736 bytes content-type:text/plain; (decoded 7bit)

> I want to replace a tact-switch in an automotive

I think capacitive would work best in a car. Around the home
you can generally use mains pick-up. Touch switches I've made
have a CMOS oscillator, around 75kHz, which feeds into a
bridge rectifier. The touch pad is part of the bridge. When a
finger is brought in proximity, the voltage from the bridge goes
down and a comparator changes state. A small pad would
probably need direct touch, but a larger pad (100mm square)
will detect a hand through 80mm of wood

The circuit attached might be a bit big for you, but you get the
idea

A similar technique can be used with a flip-flop or counter for a
reciprocating output ie touch-on, touch-off



part 2 2458 bytes content-type:image/gif; (decode)


part 3 35 bytes content-type:text/plain; charset="us-ascii"
(decoded 7bit)

2008\01\18@220143 by Bob Axtell

face picon face
picdude2@avn-tech.com wrote:
{Quote hidden}

I had a successful design using a built-in optical IR RCVR/XMTTR. The
device is designed  to be used  to
detect reflective strips, but I noticed that they worked on glass and
plastic; the finger placed above the sensor
caused a better reflection than the sensor alone, although I had to
drive it harder so I  pulsed it, taking readings
every 100mS.. These are very small, smaller than a PS2501-1 DIP device.

It would probably work better with the hole... but sealing it might be a
problem.

--Bob A

2008\01\18@232214 by cdb

flavicon
face
No one has mentioned the uChip touch/capacitive sensing idea.

Colin

:::: I want to replace a tact-switch in an automotive PIC application
:::: with some type
:::: of touch-switch, and wondering what options exist.  Also, PCB-
:::: space
:::: is limited, so it
--
cdb, colinspamKILLspambtech-online.co.uk on 19/01/2008

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







--
No virus found in this outgoing message.
Checked by AVG.
Version: 7.5.516 / Virus Database: 269.19.7/1232 - Release Date: 1/18/2008 7:32 PM


2008\01\18@233943 by Mohit Mahajan (Lists)

picon face
www.microchip.com/mtouch

cdb wrote:
{Quote hidden}

2008\01\19@013652 by Justin Richards

face picon face
I always wanted to experiment using a LED in a bezel as a touch switch
(if there was enough ambient light, which may not be the case for
automotive applications).

The idea was that when a finger was placed over the bezel it could
detect the drop in light and then drive the led on with pulses. Again
measure light levels between the pulses to see if it has been
'pressed' again.

I suspect that if the LED has just been pulsed on will take some
settling time before it is sensitive to changes in ambient light.

Justin

On Jan 19, 2008 1:39 PM, Mohit Mahajan (Lists) <EraseMEmohit.listsspam_OUTspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

2008\01\19@020651 by cdb

flavicon
face
For your idea, why not just use a reflective opto switch? Optek have one with a Schmitt trigger TTL output.

Colin

:: I always wanted to experiment using a LED in a bezel as a touch
:: switch
:: (if there was enough ambient light, which may not be the case for
:: automotive applications).
::
:: The idea was that when a finger was placed over the bezel it could
:: detect the drop in light and then drive the led on with pulses.
:: Again
:: measure light levels between the pulses to see if it has been
:: 'pressed' again.
--
cdb, @spam@colinKILLspamspambtech-online.co.uk on 19/01/2008

Web presence: http://www.btech-online.co.uk  

Hosted by:  http://www.1and1.co.uk/?k_id=7988359







--
No virus found in this outgoing message.
Checked by AVG.
Version: 7.5.516 / Virus Database: 269.19.7/1232 - Release Date: 1/18/2008 7:32 PM


2008\01\19@030915 by Justin Richards

face picon face
Thanks,

I always wandered what they were called.  I used to refer to them as a
pig-snout pairs as the ones I found in Video Records looked like a pig
snout.  I tried googling for pig-snout pair when I was looking for
shaft speed encoder but didnt get very far.

I liked the idea of using a LED because you get a touch switch and
On/Off indicator in the same part (if it works).

Might go and play with a cro and LED to see what I get.

Cheers Justin


On Jan 19, 2008 4:06 PM, cdb <KILLspamcolinKILLspamspambtech-online.co.uk> wrote:
{Quote hidden}

2008\01\19@101618 by Brendan Gillatt

flavicon
face
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

spamBeGonepicdude2spamBeGonespamavn-tech.com wrote:
| Hi all,
|
| I want to replace a tact-switch in an automotive PIC application with
some type
| of touch-switch, and wondering what options exist.  Currently that
application
| has an acrylic front, which has a small hole for the stem of the tact
switch
| (plus some LED displays etc on the inside).  The touch switch would
need to be
| small and low cost.  I don't expect it to be $0.10 as the tact switch
is, but I
| figure up to $1 would be nice (in quantity).  Also, PCB-space is
limited, so it
| needs to be not much larger than a 6mm x 6mm tact switch.  Say 10mm x
10mm would
| be acceptable.
|
| In my basic investigation so far (quite some time ago), I found
specialized chips
| that are a bit pricey and larger (such as Q-Prox), so I'm looking for
some other
| option or other technology, such as a discrete circuit option.  I'm
envisioning
| being able to do this with a spare PIC I/O (or two?) and some minimal
protection
| circuitry to that I/O pin.  Capactive, light-sensing, etc would be fine.
|
| Any thoughts, pointers, etc?
|
| Cheers,
| -Neil.

Believe me, the Q-Prox chips are fantastic! I can see them being a bit
expensive for long runs but if you're doing a project or less than a
thousand units it's probably not worth the effort in developing a new system.

If you replace more than one switch the price per switch goes down
dramatically with the Q-Prox chips.

Microchip offer some capacitive sensing examples in an application note
somewhere, along with some assembly.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (MingW32)

iD8DBQFHkhRXuv4tpb9qDZQRAhENAJ9uqTF4Cl9iscrkb5fbQPzcakl4cACeLzT+
WQEetiuVO6/Zrj6901WcZ+U=
=LNGE
-----END PGP SIGNATURE-----

2008\01\21@095320 by Eoin Ross

flavicon
face
Cypress Semi also make a big noise about their CapSense systems.

http://www.onfulfillment.com/cypressstore/Product.aspx?d=30&p=987&sid=205

CY3270              PSoC FirstTouch Starter Kit           US$30

The CY3270 PSoC FirstTouch Starter Kit provides a quick, easy, and
affordable way to evaluate the integration, flexibility and real
mixed-signal programmability of PSoC mixed-signal arrays. Without
writing or debugging a single line of "C" or assembly code, you can
experience the power of PSoC mixed-signal arrays performing the
following four out of the box designs with two thumb-drive form factor
boards:
# CapSense* Touch Sensing controlling the color of LEDs
# Temperature Sensing controlling the color and blinking rate of 3 LED
and the sound of a buzzer
# Light Sensing controlling the intensity of a LED
# CapSense Proximity Sensing controlling the color of LEDs
Other features optimized for PSoC evaluation are as follows:
# Additional designs possible utilizing above sensing and control
functionality
# Functional pins are accessible for further evaluation and
development
# Detachable multifunction expansion card enables adding the kit to
system boards
# USB connectivity for convenient plug and play operation


>>> TakeThisOuTbrendanEraseMEspamspam_OUTbrendangillatt.co.uk 19 Jan 08 10:16:39 >>>
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

RemoveMEpicdude2spamTakeThisOuTavn-tech.com wrote:
| Hi all,
|
| I want to replace a tact-switch in an automotive PIC application
with
some type
| of touch-switch, and wondering what options exist.  Currently that
application
| has an acrylic front, which has a small hole for the stem of the
tact
switch
| (plus some LED displays etc on the inside).  The touch switch would
need to be
| small and low cost.  I don't expect it to be $0.10 as the tact
switch
is, but I
| figure up to $1 would be nice (in quantity).  Also, PCB-space is
limited, so it
| needs to be not much larger than a 6mm x 6mm tact switch.  Say 10mm
x
10mm would
| be acceptable.
|
| In my basic investigation so far (quite some time ago), I found
specialized chips
| that are a bit pricey and larger (such as Q-Prox), so I'm looking
for
some other
| option or other technology, such as a discrete circuit option.  I'm
envisioning
| being able to do this with a spare PIC I/O (or two?) and some
minimal
protection
| circuitry to that I/O pin.  Capactive, light-sensing, etc would be
fine.
|
| Any thoughts, pointers, etc?
|
| Cheers,
| -Neil.

Believe me, the Q-Prox chips are fantastic! I can see them being a bit
expensive for long runs but if you're doing a project or less than a
thousand units it's probably not worth the effort in developing a new
system.

If you replace more than one switch the price per switch goes down
dramatically with the Q-Prox chips.

Microchip offer some capacitive sensing examples in an application
note
somewhere, along with some assembly.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.7 (MingW32)

iD8DBQFHkhRXuv4tpb9qDZQRAhENAJ9uqTF4Cl9iscrkb5fbQPzcakl4cACeLzT+
WQEetiuVO6/Zrj6901WcZ+U=
=LNGE
-----END PGP SIGNATURE-----

2008\01\22@135104 by Walter Banks

picon face


"picdude2EraseMEspam.....avn-tech.com" wrote:

> I want to replace a tact-switch in an automotive PIC application with some type
> of touch-switch, and wondering what options exist.

http://www.bytecraft.com/Touch_Sensitive_Switch

We built several special purpose keypads  using this technology
in weather resistant cases.

w..


2008\01\22@175258 by alan smith

picon face
Microchip now has an inductive sense switch.  Its pretty new, so it might not even be on the website but talk to your local rep or FAE about it.  There is a demo kit floating around for it.
     
---------------------------------
Be a better friend, newshound, and know-it-all with Yahoo! Mobile.  Try it now.

More... (looser matching)
- Last day of these posts
- In 2008 , 2009 only
- Today
- New search...