I'd use a LED plus signal diode: LED (c) to ground, LED (a) to Vdd=20 via suitable resistor, diode (c) to LED (a), diode (a) to=20 signal_to_be_clamped. Pick the appropriate LED color for the desired=20 voltage drop (plus 0.6V for the diode drop). Bonus: you get a power indicator. I regularly use a/d over-sampling to increase my signal's resolution=20 but you need to be aware that accuracy does not increase at the same=20 rate as resolution. In other words, accumulating enough samples to=20 double your apparent resolution does NOT give the same increase in accuracy= .. dwayne At 01:24 AM 5/5/2016, Richard Prosser wrote: >Low voltage zeners tend to have a fairly soft turn on point - not what >you want. You may even find a LED of the right type could be better, >or a string of std. diodes. Better again might be an opamp to clamp >the maximum level. (And amplifiy). > >RP > > >On 5 May 2016 at 17:53, Neil wrote: > > Hi all, > > > > I'm looking for a way to get more resolution on a PIC32 A/D input (I'll > > actually be using a Chipkit board) for a low-voltage input signal. > > Official spec =3D as good as I can get it (in limited time). The > > sensor/amp puts out a 0-10V signal for 0-to-10 Kg force, but I only nee= d > > to measure about 0 to 0.5kg (up to 0.5V), so only 5% of the full range. > > Voltage-dividing the signal reduces the resolution/range, so I'll > > protect the A/D input with a zener to clamp the signal instead. > > > > Now, with a 2V external reference (lowest allowed by datasheet), 0 to > > 0.5V nets only 8-bit resolution. I'd really like to get better. Other > > than adding an op-amp into the circuit, is there any other trick to bum= p > > the resolution up? > > > > If I do happen to have a workable op-amp on hand (though I doubt) to > > amplify the signal x4, I know that the zener will affect the linearity > > of the signal as it gets close to the zener voltage, but would a 3-ish > > volt zener cause any noticeable error at around 2V? Or is there some > > parameter that indicates that a zener would have a "sharper" knee? > > > > Cheers, > > -Neil. --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA 780-489-3199 voice 780-487-6397 fax 888-489-3199 Toll Free www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .