Charge Transfer using a PIC

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Hello,

Can anybody provide any information on using the charge transfer =
technique using a PIC.

I have read a few papers that provide a brief explanation of how to =
impliment it using just one fixed capacitor (integrator) and two IO =
pins.

I have tried to re-create it but can't get it to work. I have no idea of =
the timings involved or even the value for the integrating capacitor.

There is an example in chapter 17 of 'Programming and customizing the =
Basic Stamp' but I am having trouble getting hold of this book at a =
sensible price in the UK (A3%59!!!!!!!!)

Best Regards,

Geoffrey.


Re: Charge Transfer using a PIC
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Are you looking for something like these Microchip application notes?

http://www.microchip.com/1010/suppdoc/appnote/all/an700/index.htm

http://www.microchip.com/1010/suppdoc/appnote/all/an863/index.htm

Rob Young
snipped-for-privacy@ieee.org

Re: Charge Transfer using a PIC
Thanks Rob for the links, but they're not quite what I had in mind.
Below is a link to the article that got me thinking, it also has a nice use
of the PIC rail diodes for RFID pick-up.

http://www.merl.com/papers/TR2002-21 /

I have emailled the authors but so far no response.

In the article they use two IO lines to charge the test capacitor (could be
PCB tracks or metal surface to act as a proximity detector) then share its'
charge with a known capacitor and measure this voltage for a threshold value
(being the digital input threshold of one of the IO lines). This process is
repeated until the unknown capacitor has charged the known capacitor to a
threshold. The number of times this charge process is repeated is
proportional to the ratio of the two capacitors.

It looks to be a great technique, only one external capacitor and the
sensitivity to use the capcitive plates as a proximity detector :
http://www.merl.com/papers/TR2003-35 /

The technique is known as charge transfer and is featured in chapter 17 of
'Programming and customizing the Basic Stamp' but it costs a fortune and I
will have to wait several weeks for a copy to be shipped. I just thought
someone might have some details.

If I do manage to get some details and get something working I will post it
on the internet as it looks like a useful technique.

Regards,

Geoffrey.

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