Re: Re: Led-switch Alternative

[ian.bird@xxxxxxxxxxxxxxxxxxxxxxx]

Hi Gary

As I mentioned I have the QT160 6 button version and their demo board which
runs off a PP3 9 volt battery. I also have one of the older 4 button ones
but that too used a 9 volt battery. In demo mode and sitting on a bench
they seem to be very reliable. Pick it up though and it all goes to pot as
the capacitance varies wildly with how tight you hold it and where. Since I
am not planning a hand held device this is not really an issue.

Other points to note are the power supply. Give the complete circuit its
own power regulator and associated decoupling circuitry etc. They are very
sensitive to power fluctuations. Observe their design notes on tracking and
where and where not to run it. Have a ground plane (meshed will do as well
as solid) around the chip and associated circuitry. Finally smt stuff makes
these work much better. Some of them are only available in smt anyway now.

If you can make your own circuitboards then smt is not a big problem. There
are a couple of rules of thumb for good results but it is well within the
capabilities of the home setup. I have started writing a page on how I do
this and whilst it on my site all the pictures are missing and some of the
hints stuff - basically it is not finished. Must do that soon ;-))

Ian






"Gary"
<questuk1@hotmail        To:       ukha_d@xxxxxxx
.com>                    cc:       (bcc: Ian Bird/CV/Novartis)
Subject:  [ukha_d] Re: Led-switch Alternative
19/03/2005 14:12
Please respond to
ukha_d








Hi,

I once tried the qprox touch buttons, using there demo board and i
found it very unreliable, sometimes worked sometimes didn't, it was
powered by 2 AAA batteries.

How reliable have you found them?

I must admit i only played with them for 10 mins as i was
dissapointed. Any tips on how to get them working reliably?


Thanks


Gary


--- In ukha_d@xxxxxxx, ian.bird@c... wrote:
> Hi Frank
>
> I am also experimenting with these for some touch buttons I am
building. I
> am using the QT160 parts (6 buttons), which ones are you looking at?
>
> If you are going to have your LED's in the same plate you are using
for
> touch sensing you will need to capacitively decouple every component
of
> the LED i.e. one cap before the LED, one after it and another after
the
> resistor. I also asked Quantum about dimming using PWM for LED's in
this
> situation and they did not know as they had never tried it. The
potential
> problem being the continual switching of the LED on and off might
upset
> the capacitance field sensing circuitry. I guess the alternative
would be
> something like a digital pot but I don't know whether that would
work or
> not.
>
> From what I can see it would not be too difficult to make a one or
up to
> six button switch plate and give it the driving logic to switch low
> voltage coils in relays. These relays could then control the LD11
units as
> Gareth would like to do.








______________________________________________________________________
The CIBA Vision email address format has changed to
firstname.lastname@xxxxxxx.  Please update your address book
accordingly.
______________________________________________________________________