The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: John Popelish
Organization: This space not available for advertising.
X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Humidity sensor - peculiar behavior
Date: Sun, 05 Jan 2003 02:13:10 GMT
NNTP-Posting-Date: Sat, 04 Jan 2003 21:13:10 EST
Steve Turner wrote:
> Spehro Pefhany wrote:
> >P.S. I see you've eliminated the possibility of oscillation of the
> >follower in your original post, but what about the sensor output?
> I've looked at both the sensor output and the follower output with a
> scope. The sensor output shows some noise, perhaps 10 mV p/p, plus
> very sharp spikes of about 400 mV p/p at about 5.9 KHz. The follower
> output shows a 5.9 KHz fundamental signal as well, attenuated (maybe
> 50 mV p/p), full of harmonics with a decaying envelope. I don't know
> if any of this is relevant to anything. It is definitely not square
> wave and looks nothing like oscillating op amps that I've seen in the
My guess is that the device contains a 5.9kHz internal oscillator and
a full bridge driver (probably CMOS) and a capacitance to voltage
converter circuit that drives the output but leaks some of the
oscillator edge to the output. This would imply that the chip should
have a but if bypass capacitor across the supply pins, and a low pass
filter between the output and the follower to keep the spikes from
causing any nonlinear effects with the opamp input. With a single
opamp follower it is very simple to produce up to a 3 pole low pass
voltage controlled voltage source (Sallen-Key) filter with a very
accurate gain of 1. But just a series resistor and shunt capacitor
before the follower may suffice.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup