>Hi,
>  I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
>anyone tried out the circuit on that page? Does it work?
>  Even better - does anyone know if there's a way to reduce the number of I/O
>lines in a similar way to a matrix of pushbuttons? I want something small,
>with at least 12 keys, hooked up to a 16F628A (eventually). The whole
>device - including the 3x4 keypad array - is going to be around the size of a
>credit card.
>  Am I stuck with normal mechanical switches?
>
>Thanks.
>  
>

> Hi,
>   I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
> anyone tried out the circuit on that page? Does it work?
>   Even better - does anyone know if there's a way to reduce the number of
> I/O lines in a similar way to a matrix of pushbuttons? I want something
> small, with at least 12 keys, hooked up to a 16F628A (eventually). The
> whole device - including the 3x4 keypad array - is going to be around the
> size of a credit card.
>   Am I stuck with normal mechanical switches?
>
> Thanks.

>Hi,
>  I've just been looking at <http://www.bytecraft.com/touchsw.html> - has
>anyone tried out the circuit on that page? Does it work?
>  Even better - does anyone know if there's a way to reduce the number of I/O
>lines in a similar way to a matrix of pushbuttons? I want something small,
>with at least 12 keys, hooked up to a 16F628A (eventually). The whole
>device - including the 3x4 keypad array - is going to be around the size of a
>credit card.
>  Am I stuck with normal mechanical switches?
>
>Thanks.
>  
>

>-----Original Message-----
>From: @spam@piclist-bouncesKILLspammit.edu [KILLspampiclist-bouncesKILLspammit.edu]
>On Behalf Of RemoveMEolin_piclistTakeThisOuTembedinc.com
>Sent: 07 September 2004 12:09
>To: Microcontroller discussion list - Public.
>Subject: Re: [PIC]: Touch sensitive switches?
>
>
>Cwebber wrote:
>>> One of the best ways to connect switches to minimize PIC pins is to
>>> wire the switches so that when pressed, they present a different
>>> voltage level on a PIC analog input pin.
>>
>> If I remember correctly microchip has an appnote called "trick's and
>> tips" for the 12F628 that includes the method that Bob describes
>> above.
>
>That would be a good trick, considering that there is no
>12F628 in the first place, and neither the 12F629 nor 16F628
>have A/D inputs anyway.

>In message <009c01c494dd$148e7460$7c01a8c0@y2k>
>          Russell McMahon <RemoveMEapptechEraseMEEraseMEparadise.net.nz> wrote:
>
>  
>
>> Is that the one they are bringing out in TO92 ?
>>
>>(Power version in TO220 with 2 amp I/O)
>>    
>>
>
>Sounds nice, but how are you supposed to program it if it only has one I/O
>pin? :)
>

> At 03:35 PM 9/6/2004, Philip Pemberton wrote:
>>Hi,
>>   I've just been looking at <http://www.bytecraft.com/touchsw.html> -
>> has
>>anyone tried out the circuit on that page? Does it work?
>>   Even better - does anyone know if there's a way to reduce the number
>> of I/O
>>lines in a similar way to a matrix of pushbuttons? I want something
>> small,
>>with at least 12 keys, hooked up to a 16F628A (eventually). The whole
>>device - including the 3x4 keypad array - is going to be around the size
>> of a
>>credit card.
>
> Have you looked at Motorola's "e-field" sensing chips?  They might do what
> you need.  In addition, Qprox has touch sensitive matrix keypad chips that
> work well.  I haven't used the Motorola stuff yet but I think highly of
> Qprox.
>
> I've been using a couple of different approaches for most of my touch
> stuff
> - one is loosely based upon Don Lancaster's touch switch as described in
> his "CMOS Cookbook", the other uses a CMOS 555 timer in free-running
> astable mode.  Both techniques have worked very well in many public
> displays (museums and interpretive centres) that we've built controls for
> over the past 20 years.
>
> The 555 timer version works particularly well - there is no direct contact
> to the circuit, allowing for pretty darned good ESD protection.  Our
> standard demo involves getting the client to try destroying the unit with
> anything he can think of - we give him the largest piezo sparker I've been
> able to find - it easily generates 1" sparks.  The unit glitches when hit
> with that nasty fellow but recovers all by itself.  No units have ever
> failed in the field.
>
> The downside of the '555 version is the relatively large footprint
> required
> - the touch switches I've been building have pads that are almost 0.75"
> square.  I'd think the smallest size that would work is about 0.5" square.
>

>
> The circuit at the provided URL seems like it'd have ESD sensitivity
> problems.
> Harold
>
> > At 03:35 PM 9/6/2004, Philip Pemberton wrote:
> >>Hi,
> >>   I've just been looking at <http://www.bytecraft.com/touchsw.html> -
> >> has
> >>anyone tried out the circuit on that page? Does it work?

>On Mon, 06 Sep 2004 15:59:11 -0700, Bob Axtell <KILLspamengineerspamBeGonecotse.net> wrote:
>  
>
>>One of the best ways to connect switches to minimize PIC pins is to wire
>>the switches so that when pressed, they present a different voltage
>>level on a
>>PIC analog input pin. I've sucessfully used 8 switches on a single PIC
>>analog input. Just hook 'em up so that a each different resistor value
>>causes the
>>voltage at the analog pin to be 1/8FS, 1/4FS, 3/8FS, etc etc. A reading
>>of FS means NO switch is pressed. If I had 12 switches, I'd connect them to
>>2 PIC A/D pins, 6 on each pin.
>>    
>>
>
>Bob, can you explain how you handle simultaneous keypresses?
>
>Regards,
>another Bob
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>  
>