Make sure to use the BAV199 or something similar. 5nA leakage guaranteed at 75V reverse (room temp), tough to beat that and you get a dual-diode for under 5c a pop in reels.
-- Regards, Joerg http://www.analogconsultants.com/
Why would you do that? Capacitive sensing isn't that hard to get right with the chips available. There must be something else you are doing wrong. Maybe switch to a different brand. From what I've heard the capacitive touch chips from Cypress are the best. This chip was highly recommended:
I never got round to testing it myself because the client choose to use a touchscreen + TFT.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Indeed, though the voltage drop is kind of high. A subsequent series resistor will easily cushion the leftovers against the uC's input diodes.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
That's the trick, the "subsequent resistor". Then it won't matter whether the diode drops 1.5V or 2V.
-- Regards, Joerg http://www.analogconsultants.com/
I know I'm 'preaching to the choir' but the plane is a capacitor at low enough frequency. Higher frequencies it's actually more like a transmission line whose characteristic impedance starts out as a function of plane separation [that's why thinner is better, because this Zo is THE limiting factor] It's like transmission lines in 3D, in parallel, so difficult to envision. At high frequency there's not much area involved so the capacitance is low, then at lower frequency as the wave spreads, there is more area and there is more capaictance. Think like a transmission line whose Zo drops as the wave spreads, kind of like Zo(f) When f is high, Zo goes to some value, then when f is low, the Zo is dropping like a rock 10 ohm, 1 ohm, 0.1 ohm etc depending on size of the board. The trick with caps is to place them judiciously so that the board planes 'look' like they continue out to infinity.
From reading your posts, I thinkyou know this stuff already. Has anybody calculated the Zo(f) for PCB planes?
If you can get a copy of the AppNote from Ansoft describing using their HFSS to reduce number of bypass caps it's worth reading. Going from something like 60 caps down to 12 and placing them properly [may have misremembered] substantially IMPROVED the performance of the PCB by reducing noise on the planes.
Aha, thanks!
Thanks to you as well. I have a TL431, I think I will put that into the device.
Things are starting to sound rather difficult, e.g. in Roberts analysis... I suddenly remember why I gave up electronic engineering a long time ago and switched to technical software engineering ;-), I do not like all these physics, why can't components not just behave as ideal components? Again ;-) (but I *am* glad that I usually do not have with these matters - and all the more gratefull for the assistance of the members of this group).
Thanks again to all of you!
Yours sincerely, Rene
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