Searching \ for '[EE] Material suggestions for slide switch' 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/index.htm?key=material+suggestions
Search entire site for: 'Material suggestions for slide switch'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Material suggestions for slide switch'
2010\02\05@172630 by ivp

face picon face
Hi all,

I've got a project which involves selecting from a menu with a long
slide switch. It will be made of a piece of PCB about 200mm long
with 20 tracks going off to a PIC ADC. The user control is a slider,
which moves a finger to complete the circuit. The idea is that the
position of the circuit completion means a distinct voltage at the ADC,
like a 1-way 20-pole rotary switch rolled out

20 positions is a separation of 50 in the ADC. If that turns out to be
too fine then the 20 can be split into 4 groups of 5, using 4 ADC. The
PIC has nothing else to do except pass this information on so pins use
is not a problem

My concern is what material to use for the tracks. As this is a one-off,
and I haven't found out what expense is involved, I don't know whether
gold flashing or carbon would be an option. And might not be hard enough.
Bare copper is probably out, so too perhaps tinned tracks. I can imagine
poor contact and noise after a time

I've got some thin tin plate, as used for screening boxes, which might
do. Had it for a while and it still looks bright enough but don't know if
it would corrode if abraded by a moving contact. Maybe some brass
shim, but that gets a patina pretty readily

Any suggestions or experiences ?

wbr

2010\02\05@173401 by Bob Blick

face
flavicon
face

On Sat, 06 Feb 2010 11:25:50 +1300, "ivp" said:
> Hi all,
>
> I've got a project which involves selecting from a menu with a long
> slide switch. It will be made of a piece of PCB about 200mm long
> with 20 tracks going off to a PIC ADC. The user control is a slider,
> which moves a finger to complete the circuit. The idea is that the
> position of the circuit completion means a distinct voltage at the ADC,
> like a 1-way 20-pole rotary switch rolled out

Hi Jinx,

You may have already thought of using a rotary potentiometer with a
~100mm diameter pulley on it, and use a string attached to the slide, in
the style of a dial cord in old radios.

Just a thought.

Cheerful regards,

Bob

--
http://www.fastmail.fm - Choose from over 50 domains or use your own

2010\02\05@174359 by dpharris

picon face
Quoting ivp <spam_OUTjoecolquittTakeThisOuTspamclear.net.nz>:

{Quote hidden}

Why not a slide potentiometer?  If you need indents, then perhaps you could add
them.  Likely to hold up better and easy to obtain, eg
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PP1045SD-ND

David


2010\02\05@180216 by dpharris

picon face
Quoting .....dpharrisKILLspamspam@spam@telus.net:

{Quote hidden}

PS -- oops, these are not long enough for your application --- I like the rotary
pot with pulley idea of Bob's.

David


2010\02\05@180555 by ivp

face picon face
> Why not a slide potentiometer?

It really does need to be 200mm (8") long, possibly even 250mm
if more options are added. IME slide pots can turn out to be noisiest
pots of all, and this will get plenty of use. I have thought of using the
element from a bar heater. From memory I think they're about 70
ohms. Perhaps even resistance wire

wbr

2010\02\05@183024 by ivp

face picon face
> You may have already thought of using a rotary potentiometer with
> a ~100mm diameter pulley on it, and use a string attached to the slide,
> in the style of a dial cord in old radios.

If it's robust enough in the long term (got a bit of a downer on carbon pot
tracks but you can get conductive plastic, at a price) that might be a goer

The client has indicated he'd like the slider moved by a brass crank. !!!!
This probably means that the slider will be on a lead screw and several
turns of the crank will move the pointer from one item to the next

The reason being that this is a museum exhibit of a 1906 Edison cylinder
player, which has been motorised but originally was wound up with a
crank, so he wants to keep some of that feel to it. The selector is to pick
a song to play from a bank of WAV files

If the resolution proves too fine for the ADC to differentiate 20 positions
reliably I should be able to come up with a scheme to divide the pot travel
across more than 1 ADC

As the slider has to move a great deal further than the pot shaft some
step-down gearing would be needed to convert 200mm linear movement
via a lead screw to 270 degrees of pot rotation

I even thought of a stepper motor as a pulse-emiting encoder but can't
guarantee that it will keep track or be returned to an end stop to reset the
pulse count

My idea with a long PCB is that it would have fixed resistors and solid
detentes, thus turning the crank is a WYSIWYG. It's for public use and
something I'd rather not have to service or field complaints about

wbr

2010\02\05@184116 by Bob Blick

face
flavicon
face

On Sat, 06 Feb 2010 12:29:04 +1300, "ivp" <.....joecolquittKILLspamspam.....clear.net.nz>
said:
> > You may have already thought of using a rotary potentiometer with
> > a ~100mm diameter pulley on it, and use a string attached to the slide,
> > in the style of a dial cord in old radios.
>
> If it's robust enough in the long term (got a bit of a downer on carbon
> pot
> tracks but you can get conductive plastic, at a price) that might be a
> goer

Allen-Bradley makes long life pots that really are long life.

Back to the PC board slide switch idea, if everything is polished and
you grease the contact surfaces, it could last a long time. You could
even put rivets, screws, or other type of contact buttons on it. Or
crimp sheet metal around the edge of the board.

Cheerful regards,

Bob

--
http://www.fastmail.fm - Email service worth paying for. Try it for free

2010\02\05@185320 by sergio masci

flavicon
face


On Sat, 6 Feb 2010, ivp wrote:

{Quote hidden}

in that case what about an IR distance measuring widget in parallel with
the lead screw. IIRC these can measure distances upto about 20cm without
problems

Regards
Sergio Masci

2010\02\05@185334 by Isaac Marino Bavaresco

flavicon
face
Why don´t you simply use 20 pins of a PIC, with pull-ups, and a grounded
slider?

You could draw a sequence of copper rectangles on the board, stacked
end-to-end, each rectangle connected to one PIC pin. The slider makes
contact with just one at a time.


Regards,

Isaac


Em 5/2/2010 21:29, ivp escreveu:
{Quote hidden}

__________________________________________________
Faça ligações para outros computadores com o novo Yahoo! Messenger
http://br.beta.messenger.yahoo.com/

2010\02\05@203403 by ivp

face picon face
> even put rivets, screws, or other type of contact buttons on it. Or
> crimp sheet metal around the edge of the board.

That was my original idea, but I'm unsure about which metals will
still make good contact after some time. I guess to some extent the
action will help keep them clean if you used several point contacts
and reasonable pressure

wbr

2010\02\05@203404 by ivp

face picon face
> IR distance measuring widget

Hmmm, optical

wbr

2010\02\05@203404 by ivp

face picon face
> Why don´t you simply use 20 pins of a PIC, with pull-ups, and a
> grounded slider?

That's a thought. The processing PIC in there at the moment is a
16F88 and I was trying to multiplex a diode array as a decimal-to-
hex converter but it hasn't really 5 usable pins left without a lot of fuss.
Track selection is an after-thought addition (clients eh ?, bless 'em). As
it is now it starts at track 1 and just wraps around after track 20. If the
F88 is swapped for A PIC with one more port (eg F876) the multi-
plexing idea would work or a 40-pinner could do it on a one-to-one
basis

wbr

2010\02\05@210126 by Bob Ammerman

picon face
Well if you have a brass crank, why not just a rotary encoder on its shaft
and a zero position sensor at one end of the travel of the pointer.

-- Bob Ammerman

{Original Message removed}

2010\02\05@211914 by dpharris

picon face
Yes, that's a good suggestion.  Alternately, if you have a lead screw, then the
slider could activate a set of microswitches, which should give excellent
longevity, and be quite eay to construct and be eraltively inexpensive.    

David

with a crankQuoting Bob Ammerman <EraseMErammermanspam_OUTspamTakeThisOuTverizon.net>:

> Well if you have a brass crank, why not just a rotary encoder on its shaft
> and a zero position sensor at one end of the travel of the pointer.
>
> -- Bob Ammerman
>
> {Original Message removed}

2010\02\05@213325 by Marcel Duchamp

picon face
On 2/5/2010 6:19 PM, dpharrisspamspam_OUTtelus.net wrote:
> Yes, that's a good suggestion.  Alternately, if you have a lead screw, then the
> slider could activate a set of microswitches, which should give excellent
> longevity, and be quite eay to construct and be eraltively inexpensive.
>
> David
>
>   with a crankQuoting Bob Ammerman<@spam@rammermanKILLspamspamverizon.net>:
>
>> Well if you have a brass crank, why not just a rotary encoder on its shaft
>> and a zero position sensor at one end of the travel of the pointer.
>>
>> -- Bob Ammerman


Davids solution hits at the heart of the matter - you are digitizing the
position into discrete points (and not many of them) so although you
described an analog approach initially, thinking digitally makes some sense.

If a leadscrew nut travels along activating microswitches as it passes
them, you will always know where the contraption is set to.  The only
hurdle is power up out in the middle somewhere and knowing where you
are.  This could be handled by remembering the last place (nvram) or at
power up, always travel a bit until a microswitch gets activated and
then back up to where you just started from.

Plus requiring people to operate the hand-crank will slow their
enthusiasm for ripping back and forth on the system.

It sounds like a fun project so if possible, let us know what you final
system solution is and perhaps photos?

2010\02\05@222951 by PICdude

flavicon
face
If using a slide pot, you can change it's range mechanically ... think  
gear-shift in a car.

Alternatively, I saw a very nice (and quite reliable) "slide  
touch-switch" implementation using on of the enhanced PIC16F's at a  
microchip seminar recently.  I was quite impressed and tested it with  
a few sheets of paper between the contacts and my finger, which also  
worked beautifully.

If that's not an option, then how about using whatever mechanical  
switch mechanism you come up with, together with a belt plus 2 pulleys  
(in a loop) and mounting a quadrature encoder on one pulley.

Cheers,
-Neil.


Quoting KILLspamdpharrisKILLspamspamtelus.net:
>
> Why not a slide potentiometer?  If you need indents, then perhaps  
> you could add
> them.  Likely to hold up better and easy to obtain, eg
> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=PP1045SD-ND
>
> David


2010\02\05@223533 by PICdude

flavicon
face
Quoting ivp <RemoveMEjoecolquittTakeThisOuTspamclear.net.nz>:

> The client has indicated he'd like the slider moved by a brass crank. !!!!
> This probably means that the slider will be on a lead screw and several
> turns of the crank will move the pointer from one item to the next

Well, if you say lead-screw, then the CNC guys will tell you to stick  
an encoder on the end.

But then that also makes me think of a DRO scales.  The scales  
apparently put out serial info as to their position.  This is an  
example of one...  
http://littlemachineshop.com/products/product_view.php?ProductID=2016

Cheers,
-Neil.


2010\02\05@224045 by ivp

face picon face
> If a leadscrew nut travels along activating microswitches as it passes
> them, you will always know where the contraption is set to.  The only
> hurdle is power up out in the middle somewhere and knowing where
> you are.  This could be handled by remembering the last place (nvram)
> or at power up, always travel a bit until a microswitch gets activated
> and then back up to where you just started from.

'last played' is already held in EEPROM, but this new system means
that if the crank is turned when the power is off, then the PIC will lose
its bearings unless individual positions are uniquely identifiable

> Plus requiring people to operate the hand-crank will slow their
> enthusiasm for ripping back and forth on the system.

That is one concern, that some little wretch will spin the crank like
a foos ball game. And there is what to do at either end of the crank
travel so that the nut isn't jammed hard against the end stops. I've
suggested a felt or magnetic cluctch holding the crank to the screw so
that only a certain amount of force can be transmitted. Possibly the
thread could be tapered off so the nut is free-wheeling and re-threaded
by a spring but I imagine a cross-threading happening very easily

> It sounds like a fun project so if possible, let us know what you final
> system solution is and perhaps photos?

Hopefully I'll be doing that quite soon

wbr

2010\02\05@224434 by ivp

face picon face
> The scales apparently put out serial info as to their position

Absolute position is what's needed, more so than just the number
of transitions between fixed points. Unless the pointer is moved
to a home position (like a HDD) then a simple pulse system won't
be dependable

wbr

2010\02\05@224612 by Dave Tweed

face
flavicon
face
ivp wrote:
> The client has indicated he'd like the slider moved by a brass crank. !!!!
> This probably means that the slider will be on a lead screw and several
> turns of the crank will move the pointer from one item to the next
>
> The reason being that this is a museum exhibit of a 1906 Edison cylinder
> player, which has been motorised but originally was wound up with a
> crank, so he wants to keep some of that feel to it. The selector is to pick
> a song to play from a bank of WAV files

Interesting!

Did you know that there are people who are still making wax cylinders for
Edison machines? I recently saw a presentation in which they were re-creating
an old-time acoustic recording session. You wouldn't believe the gyrations
they went through while recording in order to get a decent-sounding playback.
Between the lousy dynamic range (high noise floor) and terribly non-flat
frequency response, you basically had to do a lot of "pre-compensation" of
the sound balance just to get something recognizable back out.

> My idea with a long PCB is that it would have fixed resistors and solid
> detentes, thus turning the crank is a WYSIWYG. It's for public use and
> something I'd rather not have to service or field complaints about

If I were you, I'd seriously consider non-contact solutions, such as
capacitive sensing.

For example, the brass crank could move a brass "pointer" along the surface
of the PCB, almost but not quite touching it. Sensor pads built into the PCB
artwork (sealed underneath the soldermask) would detect the presence of the
pointer at particular locations.

There are many ways to do multi-point capacitive sensing with low parts
count these days, anything from dedicated chips to ordinary I/O pins on
general-purpose microcontrollers. Usually, you just need one or two passive
components per point sensed, which compares favorably with your resistive
divider.

-- Dave Tweed

2010\02\05@225440 by ivp

face picon face

> If using a slide pot, you can change it's range mechanically ... think  
> gear-shift in a car.

The client is thinking 9mm or 10mm distance between track names in
the playlist (= 171mm or 190mm travel overall by the pointer) and a
pot is around 60mm so a 3:1 reduction gear would do the conversion.
He had a printout the other day on an A4 but I don't have a copy so
can't confirm the distance he picked

A good little thought exercise

wbr

2010\02\05@230017 by PICdude

flavicon
face
Quoting ivp <spamBeGonejoecolquittspamBeGonespamclear.net.nz>:

>> The scales apparently put out serial info as to their position
>
> Absolute position is what's needed, more so than just the number
> of transitions between fixed points. Unless the pointer is moved
> to a home position (like a HDD) then a simple pulse system won't
> be dependable
>
> wbr
> --


I'm pretty sure that it's absolute.  When I switch off/on a digital  
caliper, IIRC it comes back on with the last position.  I am not in  
the U.S. currently, so can't check.  FWIW, these scales are hacked  
digital calipers (the cheap chinese ones).  Someone figured out the  
output stream some years ago, and now these off-the-shelf DRO's use  
modified versions of those calipers as the scales.

I kinda like the IR distance-measuring solution someone else posted,  
but then why not just put some "special" paint/tape (like reflective  
perhaps) in an inconspicuous area and have a camera use edge-detection  
to find the position?  ...Rube Goldberg?

Cheers,
-Neil.



2010\02\05@230740 by PICdude

flavicon
face
Quoting ivp <TakeThisOuTjoecolquittEraseMEspamspam_OUTclear.net.nz>:

>> If using a slide pot, you can change it's range mechanically ... think
>> gear-shift in a car.
>
> The client is thinking 9mm or 10mm distance between track names in
> the playlist (= 171mm or 190mm travel overall by the pointer) and a
> pot is around 60mm so a 3:1 reduction gear would do the conversion.
> He had a printout the other day on an A4 but I don't have a copy so
> can't confirm the distance he picked
>
> A good little thought exercise
>
> wbr

Actually, if using a mechanical reduction, you might as well use a  
rotary pot for this.  Or wouldn't a rotary pot + encoder be better  
(the encoder will add accuracy to the rotary pot's info)?

That now makes me think of using a series of IR LED's in a line with  
one IR sensor under the "switch".  The IR LEDs would come on one at a  
time (cycling very rapidly) while checking the IR sensor to see which  
LED it is receiving the highest signal from it.  Ahhhh... memories of  
trying to implement a touch screen on a TRS-80 a few decades ago.

Cheers,
-Neil.



2010\02\05@232002 by ivp

face picon face
part 1 1732 bytes content-type:text/plain; format=flowed; charset="iso-8859-1"; (decoded 7bit)

> Did you know that there are people who are still making wax cylinders for
> Edison machines?

Yes, he has a reproduction plastic cylinder on the machine now with a
crystal stylus. Because this will be used so many times he's chosen to
remove the stylus and play WAV files. There are hundreds of cylinder
mp3 on the web, 100-odd of which we've sweeten up for tone and
edited for time. I put him on to

http://www.tinfoil.com/

and someone locally who was selling genuine antiques

> If I were you, I'd seriously consider non-contact solutions, such as
> capacitive sensing.

When Bob mentioned using a pulley and string like a radio the image that
popped into my head was "tuning" with the pointer and measuring the
frequency but that's way OTT

> For example, the brass crank could move a brass "pointer" along the
> surface of the PCB, almost but not quite touching it. Sensor pads built
> into the PCB artwork (sealed underneath the soldermask) would detect
> the presence of the pointer at particular locations

I've made capacitive proximity sensors like that (attached) but hadn't
thought about them in this application. The logic makes a 75kHz signal
that changes amplitude via a capacitive divider (made of the bridge
capacitances and the human body). It will detect a hand through several
centimetres of wood with a big enough pad, say 50mm x 100mm of
aluminium foil. The op-amp amplifies the amplitude change and an
integrator + Schmitt trigger removes the noise to produce a clean logic
output

I'd be interested to see any schematic you have of a simpler sensor, as
anything that has no touching parts would have a servicing advantage

wbr

part 2 2274 bytes content-type:image/gif; (decode)


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

2010\02\05@232924 by dpharris

picon face
How about optical interrupter switches?  Eg:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=H22LOI-ND

The slide would simply occlude each of the optical switches in turn.  

If it interrupts one or two at all times, then it will have a position.  To
detect n positions, you only need n/2 switches, eg for 3 switches you get 6
positions sensed: none, 1 only, 1&2, 2 only, 2&3, 3 only.  

David

Quoting Dave Tweed <RemoveMEpicspamTakeThisOuTdtweed.com>:

{Quote hidden}

> --

2010\02\05@233102 by Info

flavicon
face

> For example, the brass crank could move a brass "pointer" along the
> surface of the PCB, almost but not quite touching it. Sensor pads built
> into the PCB artwork (sealed underneath the soldermask) would detect
> the presence of the pointer at particular locations

Ok, scifi is neat i am the first to say so, but KISS still rulez the
world IMHO :-)

How about a few optocouplers C-style. Move your slider between
the "C" and you get a non-conctact and a dirt cheap solution.

Ok, next problem :-)

2010\02\05@233637 by ivp

face picon face
> Actually, if using a mechanical reduction, you might as well use a  
> rotary pot for this

I guess, although the track in a slider pot would be a little longer

> That now makes me think of using a series of IR LED's in a line with  
> one IR sensor under the "switch"

I've added a reflective IR sensor to the motor train and painted the
drive pulley half-white half-black so that the PIC can tell if the cylinder
is turning before it enables the sound

If each LED had its own individual and accurate frequency that could
be quite easily determined with CCP

Another detail - the machine has two lead screws. One is the same
fine pitch as the grooves on the cylinder. This is used to move the stylus
along, rather than the grooves themselves, which is what would have
happened originally. The other lead screw is much coarser and is used
to return the stylus back to the home position. When playing, a spring
pulls a plastic guide (which has a fine thread on one side and a coarse
thread on the other) onto the fine screw. At the end of travel, a micro-
switch, via the PIC, energises a solenoid to pull the guide off the fine
thread and onto the return thread, which is rotating the opposite way
because of the gearing

Something like that could be done with the selection thread, with a
solenoid enabling song selection only at a particular time. Any other
time the crank could be spun around without the pointer moving

wbr

2010\02\05@234405 by ivp

face picon face
> How about a few optocouplers C-style. Move your slider between
> the "C" and you get a non-conctact and a dirt cheap solution.

Yes, that would be an acceptable solution

There's a trade-off here between methods to detect position in a one-
to-one fashion (one position per PIC pin or similar) and just one PIC
pin with an analogue signal

Am I nerd or pragmatist ?

wbr

2010\02\06@001045 by Info

flavicon
face
Maybe you could add another 'finger' that selects hi/low
section of the slider and do it binary style to get more
selections from fewer pins.

I am not explaining this very good but you get the picture
or rather general idea I hope :-)

-----Ursprungligt meddelande-----
> How about a few optocouplers C-style. Move your slider between
> the "C" and you get a non-conctact and a dirt cheap solution.

Yes, that would be an acceptable solution

There's a trade-off here between methods to detect position in a one-
to-one fashion (one position per PIC pin or similar) and just one PIC
pin with an analogue signal

Am I nerd or pragmatist ?

wbr

2010\02\06@021155 by cdb

flavicon
face


:: That is one concern, that some little wretch will spin the crank
:: like
:: a foos ball game. And there is what to do at either end of the
:: crank
:: travel so that the nut isn't jammed hard against the end stops.
:: I've
:: suggested a felt or magnetic cluctch holding the crank to the
:: screw so
:: that only a certain amount of force can be transmitted.

I think what you might need is what Practical Wireless back in 1980
published something called a Polyaphon. This was totally analogue but
consisted of an etched patterned round PCB - it played like a digital
record - the 'sheet music' being encoded in the PCB patterns.

From a digital point of view it would be a binary encoded disc - have
a start mark and an end marker for positioning, and some sort of
binary encoding for the track to be played. The sensor could be
inductive or  maybe being modern, have LED's in a binary formation and
opto sensors.

Sadly I don't have the PW issues that the Polyaphon was in, just a
hazy memory.

Ah just recalled, the senors in the original were metal fingers that
'read' the track patterns. Old pianolo mechanism anyone?

Colin
--
cdb, colinEraseMEspam.....btech-online.co.uk on 2/6/2010

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

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







2010\02\06@032723 by ivp

face picon face
> I think what you might need is what Practical Wireless back in 1980
> published something called a Polyaphon

I know the issue and have it around here somewhere

wbr

2010\02\06@110029 by Peter

picon face
Simply use a long throw linear potentiometer. Up to 1 foot is not a problem and
you can use a shorter stroke unit with a cable and pulley demultiplication (one
pulley and spring = half the throw, for 20cm input output will be 10cm which is
in range for existing potentiometers). That will also decouple any violent input
from the sensor. Sensor life is also a question. The potentiometer will outlive
your switch for sure but other solutions are more durable. As someone noticed
you could use a digital caliper head and connect its output to the micro. Of
course the head would be stationary and the other jaw would move.

 Peter


2010\02\06@133157 by graham foulkes

picon face
Hi All
Capacitive pickup seems the best solution so far, especially as you have
the luxury of large areas of track. No ohmic contacts can outlast the non
contacting methods. Ohmic contacts, however ingenious, even microswitches
will eventually wear out or jam, and are degraded by environmental effects
acting on either the contact surface or the mechanics. Think moisture
(coffee), corrosion, vibration etc. A solid dielectric cover above the
tracks with the finger moving over the track positions would fit the bill.


On Fri, Feb 5, 2010 at 5:33 PM, Bob Blick <EraseMEbobblickspamftml.net> wrote:

{Quote hidden}

> -

2010\02\06@145410 by YES NOPE9

flavicon
face

For one project I built a long optical track that used 3 reflective  
opto sensors to detect black and white markings.  Quadrature  
determined where you were and every so often there was a 3rd mark that  
indicated an absolute position code would re-establish where the  
sensors were.

Optical or capacitive sensors could track position by looking at a  
digital code.  5 tracks would give you 32 positions.  The track could  
be laid out on PCB material.

You could also build a variable capacitor.   Either the plate distance  
could be varied as the crank turned or different plate size could be  
located at each position.

 Or perhaps the plate size could be determined by tracking down a  
triangular strip of copper.  If plate distance proved to be a problem  
you could reference strips on each side of the triangle

Gus.


2010\02\06@171147 by Dave Tweed

face
flavicon
face
ivp wrote:
> > For example, the brass crank could move a brass "pointer" along the
> > surface of the PCB, almost but not quite touching it. Sensor pads built
> > into the PCB artwork (sealed underneath the soldermask) would detect
> > the presence of the pointer at particular locations
>
> I'd be interested to see any schematic you have of a simpler sensor, as
> anything that has no touching parts would have a servicing advantage

There's a very clear writeup of the general-purpose I/O technique in
this contest entry:

http://www.circuitcellar.com/microchip2007/winners/DE/MT2239.html

Microchip also has some dedicated chips for multiple proximity sensors,
and pretty much any cheap PC keyboard these days uses capacitive sensing
internally -- it may be possible to hack the circuitry out of one of those.

YES NOPE9 wrote:
> Or perhaps the plate size could be determined by tracking down a  
> triangular strip of copper.  If plate distance proved to be a problem  
> you could reference strips on each side of the triangle

Mow that's actually a very interesting idea. There's a very simple technique
for converting a differential variable capacitance (even a tiny one) directly
into a DC voltage that varies by about a couple of volts or so. You could
arrange your brass finger to span across two triangular copper areas on a
PCB, such that when it moves, it covers more of one area and less of the
other. (Think of a long rectangular area with a diagonal split through it.)

I wrote the circuit up for a Circuit Cellar EQ question a while back
(INK #124, November 2000), but unfortunately, it's no longer avaialble
online. There was also information about the technique in the INK #61
(August 1995) ConnecTime column. If you're interested in pursuing this,
let me know.

(Note to self: One of these days, I need to put all of the old EQ material
up on my own website.)

-- Dave Tweed

2010\02\06@191654 by ivp

face picon face
> There's a very clear writeup of the general-purpose I/O technique in
> this contest entry:
>
> http://www.circuitcellar.com/microchip2007/winners/DE/MT2239.html

Thanks. I've downloaded the entry and will work through it

> There's a very simple technique for converting a differential variable
> capacitance (even a tiny one) directly into a DC voltage that varies
> by about a couple of volts or so

> If you're interested in pursuing this, let me know

If it's convenient for you I'd like to know more. A method I wasn't
expecting and would like to experiment

wbr

2010\02\07@134818 by Alan B. Pearce

face picon face
>My concern is what material to use for the tracks. As this is a
>one-off, and I haven't found out what expense is involved, I don't
>know whether gold flashing or carbon would be an option. And might
>not be hard enough.
>Bare copper is probably out, so too perhaps tinned tracks. I can
>imagine poor contact and noise after a time

The answer is do not use a contact slider. Microchip have a capacitive
sensor where one of the demonstration sensors is a slider. IIRC they have
one that uses 4 capacitive sensors to get a 256 position slider. When I saw
the development kit I figured it was an ideal way to make an IP67 slider ...

2010\02\07@143250 by Alan B. Pearce

face picon face
>I'd be interested to see any schematic you have of a simpler
>sensor, as anything that has no touching parts would have a
>servicing advantage

I would just buy the Microchip development kit. Get
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1406&dDocName=en541143
and use the slider examples directly in your application.

2010\02\07@160544 by ivp

face picon face
> I would just buy the Microchip [mTouch] development kit

Not sure if the client will go for that. For a variety of reasons,
99% not mine, the project is overdue and over-budget enough
already. However, the slider issue is still to be solved of course
and mTouch or sumfink like it may ultimately involve no more or
less time and money than other solutions

I notice there are a few mTouch PICs that I'd like to look at
personally one day

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2695

wbr

2010\02\07@203410 by ivp

face picon face
I wrote

> I notice there are a few mTouch PICs that I'd like to look at
> personally one day
>
> http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2695

My ooops. I thought they were PICs with built-in sensors but it's
implementations on ordinary parts

wbr

2010\02\07@213100 by Bob Blick

face
flavicon
face

On Mon, 08 Feb 2010 14:34:01 +1300, "ivp" said:
> I wrote
>
> > I notice there are a few mTouch PICs that I'd like to look at
> > personally one day
> >
> > www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2695
>
> My ooops. I thought they were PICs with built-in sensors but it's
> implementations on ordinary parts

My experience with capacitive sensing is that you must use it in a
digital format, as an encoder rather than a potentiometer. Furthermore,
in an industrial application I would rate it less reliable than optical.

I would place a lot of faith in an Allen Bradley type J potentiometer. I
bet you get 10000 operating hours from one of them.

Cheerful regards,

Bob


--
http://www.fastmail.fm - Faster than the air-speed velocity of an
                         unladen european swallow

2010\02\07@213230 by PICdude

flavicon
face
The enhanced 16F devices (such as 16F1936) have built-in capacitive  
touch-sensing capability.  AFAIK, inductive touch sensing is a future  
feature.

Cheers,
-Neil.



Quoting ivp <RemoveMEjoecolquittEraseMEspamEraseMEclear.net.nz>:

{Quote hidden}

> -

2010\02\08@002154 by ivp

face picon face
> I would place a lot of faith in an Allen Bradley type J potentiometer.
> I bet you get 10000 operating hours from one of them.

TBH I'm still inclined towards contacts or resistance / voltage, simply
because to me they're a known quantity and I think will help to get
this project finished ASAP. Other methods are just fine and I'll sample
some 16F193x to investigate the mTouch for future reference, perhaps
even swapping it for whatever goes into the project to get it going

wbr

2010\02\08@012343 by dpharris

picon face
I don't think you commented on my suggestion to use optical interruptors.  It
would seem these combine simplicity and robustness.  
David


Quoting ivp <RemoveMEjoecolquittspam_OUTspamKILLspamclear.net.nz>:

> > I would place a lot of faith in an Allen Bradley type J potentiometer.
> > I bet you get 10000 operating hours from one of them.
>
> TBH I'm still inclined towards contacts or resistance / voltage, simply
> because to me they're a known quantity and I think will help to get
> this project finished ASAP. Other methods are just fine and I'll sample
> some 16F193x to investigate the mTouch for future reference, perhaps
> even swapping it for whatever goes into the project to get it going
>
> wbr
> --

2010\02\08@030658 by ivp

face picon face
> I don't think you commented on my suggestion to use optical
> interruptors. It would seem these combine simplicity and robustness.  

Apologies. I'm thinking though about position information and what
can happen when the power is off. That also rules out simple physical
contacts. For example, if each position produces just one pulse then
the s/w has no idea of the relative position. That takes information
and that probably means driving each LED with its own frequency,
and that will mean a greater component count and some extra cost

If optos were to be used, I might make something like a circular PCB
with 5 LEDs shining through a binary pattern of holes into 5 receivers.
This would possibly become more attractive than a pot as the number
of discrete positions increased. It could even be arranged as a drum,
LEDs shining through holes rather like a tape reader

wbr

2010\02\08@044151 by cdb

flavicon
face
Folks, you are aware that uChip also do inductive touch sensing kits?
Might be closer to the current setup than changing to capacitive.

Colin


--
cdb, RemoveMEcolinTakeThisOuTspamspambtech-online.co.uk on 2/8/2010

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

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








2010\02\08@053502 by dpharris

picon face
My idea gives absolute position on start-up, but perhaps I did not explain
sufficiently.  

Construct the slider a linear slider that can move though co-linear equally-
spaced optical interruptors.  The slider is longer than the distance between
two of the interruptors, such that at any position it covers one or two of the
interrupters.  Its position is determined by the state of the interrupters.  At
one end of the slide, it is acceptable that the slide covers none of the
interrupters, since that is a unique condition.  

Eg, consider 4 interrupters A, B, C, and D, then the slider can cover none, A,
A&B, B, B&C, C, C&D, or D --- 8 positions.  

Generally, n interruptors will give 2n positions.  

Obviously this would work as well with optical reflector sensors, or contacts,
such as microswitches.    

David
Example of interrupter: http://www.fairchildsemi.com/ds/H2/H21LOI.pdf
Example of reflective sensor: http://www.fairchildsemi.com/ds/QR/QRE1113.GR.pdf



Quoting ivp <EraseMEjoecolquittspamspamspamBeGoneclear.net.nz>:

{Quote hidden}

> --

2010\02\08@072342 by ivp

face picon face

> Eg, consider 4 interrupters A, B, C, and D, then the slider can cover
> none,
> A, A&B, B, B&C, C, C&D, or D --- 8 positions.

Ah, got it

wbr

More... (looser matching)
- Last day of these posts
- In 2010 , 2011 only
- Today
- New search...