Re: 4001 as Schmitt

Jim Thompson <To-Email-Use-The-Envelope-Icon@xxxxxxxxxxxxxxx> wrote:

On Sun, 25 Jun 2006 00:11:22 GMT, "Tom Del Rosso"
<td_01@xxxxxxxxxxxxxxx> wrote:

"bruce varley" <bxvarley@xxxxxxxxxxxxxxx> wrote in message
news:449d62a0@xxxxxxxxxxxxxxxxxxx


Terry, Spehro's right on the money in terms of a solution. Put simply, it
looks like your problem is the fact that with the 10u cap on the input if
the gate, the input voltage can only change slowly, so the gate spends
significant time in the noise-prone region, and what you're seeing is
noise-induced switching during that time. Hysteresis works by being fast.

Shouldn't the feedback resistance also be much lower to speed-up switching?
Even if he changes the PI to a T like Spehro said, 10Mohms times the input
capacitance alone would produce a long switching interval like that
observed.

Use...

http://analog-innovations.com/SED/CMOS-Osc-NoClip.pdf

Eliminate U4A and R5. Change R4 to a short. Input via R1.

Then you get both noise integration, yet snap at the threshold.

...Jim Thompson

Thanks Jim. I'll try adapting that circuit and maybe use it next time.
Present circuit is already built on stripboard, with several other
sections, so want to fix it with existing 4001/4011/4013.

--
Terry Pinnell
Hobbyist, West Sussex, UK
.

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