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tech / sci.electronics.design / If you want an accurate Schmitt function, rather than a fast one...

SubjectAuthor
* If you want an accurate Schmitt function, rather than a fast one...whit3rd
+- Re: If you want an accurate Schmitt function, rather than a fast one...jlarkin
+- Re: If you want an accurate Schmitt function, rather than a fast one...Spehro Pefhany
+- Re: If you want an accurate Schmitt function, rather than a fastbitrex
`* Re: If you want an accurate Schmitt function, rather than a fastPhil Hobbs
 `- Re: If you want an accurate Schmitt function, rather than a fastPhil Hobbs

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If you want an accurate Schmitt function, rather than a fast one...

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Subject: If you want an accurate Schmitt function, rather than a fast one...
From: whit...@gmail.com (whit3rd)
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 by: whit3rd - Thu, 13 Jan 2022 01:34 UTC

what do you use?

I want to know the high and low switch thresholds, precisely,
and for them not to drift.

A '555 relies on its power rails for thresholds, and an op amp
needs rail/rail output for the positive feedback to be accurate,
neither of which is ideal for a timing component.
The old LM322 had a regulator, at least. It's as dead
as the XR2206, though.

You can drive the '555 reference, but that's a tad messy.

So, what IS still available that's near ideal, in IC form?
Three resistors, a TL431, a dual comparator and an R/S flop
would be more messy.

Re: If you want an accurate Schmitt function, rather than a fast one...

<sf5vtg5uhdelpgv2vbnj0u22hdohqmve5t@4ax.com>

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From: jlar...@highlandsniptechnology.com
Newsgroups: sci.electronics.design
Subject: Re: If you want an accurate Schmitt function, rather than a fast one...
Date: Wed, 12 Jan 2022 19:04:46 -0800
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 by: jlar...@highlandsniptechnology.com - Thu, 13 Jan 2022 03:04 UTC

On Wed, 12 Jan 2022 17:34:26 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

>what do you use?
>
>I want to know the high and low switch thresholds, precisely,
>and for them not to drift.
>
>A '555 relies on its power rails for thresholds, and an op amp
>needs rail/rail output for the positive feedback to be accurate,
>neither of which is ideal for a timing component.
>The old LM322 had a regulator, at least. It's as dead
>as the XR2206, though.
>
>You can drive the '555 reference, but that's a tad messy.
>
>So, what IS still available that's near ideal, in IC form?
>Three resistors, a TL431, a dual comparator and an R/S flop
>would be more messy.

If you are doing timing with an RC, you can charge the cap through a
resistor from the same voltage that sets the thresholds. Then the
power supply voltage drifts don't matter much.

We use an RC and a dac+comparator to make programmable time delays. If
the charging supply is ratiometric on the DAC reference, it's stable.

--

I yam what I yam - Popeye

Re: If you want an accurate Schmitt function, rather than a fast one...

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From: speffS...@interlogDOTyou.knowwhat (Spehro Pefhany)
Newsgroups: sci.electronics.design
Subject: Re: If you want an accurate Schmitt function, rather than a fast one...
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 by: Spehro Pefhany - Thu, 13 Jan 2022 05:32 UTC

On Wed, 12 Jan 2022 17:34:26 -0800 (PST), whit3rd <whit3rd@gmail.com>
wrote:

>what do you use?
>
>I want to know the high and low switch thresholds, precisely,
>and for them not to drift.
>
>A '555 relies on its power rails for thresholds, and an op amp
>needs rail/rail output for the positive feedback to be accurate,
>neither of which is ideal for a timing component.
>The old LM322 had a regulator, at least. It's as dead
>as the XR2206, though.
>
>You can drive the '555 reference, but that's a tad messy.
>
>So, what IS still available that's near ideal, in IC form?

Available and near ideal (but requires an external reference and $$)
LTC1042

https://www.analog.com/media/en/technical-documentation/data-sheets/1042fa.pdf

>Three resistors, a TL431, a dual comparator and an R/S flop
>would be more messy.

I've used an non-RR op-amp switching a CMOS analog switch, say 1/3 of
a 4053. You can use a voltage divider from a reference for the
thresholds. Easy-peasy.
--
Best regards,
Spehro Pefhany

Re: If you want an accurate Schmitt function, rather than a fast one...

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 by: bitrex - Thu, 13 Jan 2022 05:38 UTC

On 1/12/2022 8:34 PM, whit3rd wrote:
> what do you use?
>
> I want to know the high and low switch thresholds, precisely,
> and for them not to drift.
>
> A '555 relies on its power rails for thresholds, and an op amp
> needs rail/rail output for the positive feedback to be accurate,
> neither of which is ideal for a timing component.
> The old LM322 had a regulator, at least. It's as dead
> as the XR2206, though.
>
> You can drive the '555 reference, but that's a tad messy.
>
> So, what IS still available that's near ideal, in IC form?
> Three resistors, a TL431, a dual comparator and an R/S flop
> would be more messy.

Cheep and cheerful:

<https://www.dialog-semiconductor.com/products/greenpak/slg46120>

Re: If you want an accurate Schmitt function, rather than a fast one...

<e87769ba-77a1-f744-f084-2a10b683a442@electrooptical.net>

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Newsgroups: sci.electronics.design
Subject: Re: If you want an accurate Schmitt function, rather than a fast
one...
Date: Thu, 13 Jan 2022 11:34:35 -0500
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 by: Phil Hobbs - Thu, 13 Jan 2022 16:34 UTC

whit3rd wrote:
> what do you use?
>
> I want to know the high and low switch thresholds, precisely,
> and for them not to drift.
>
> A '555 relies on its power rails for thresholds, and an op amp
> needs rail/rail output for the positive feedback to be accurate,
> neither of which is ideal for a timing component.
> The old LM322 had a regulator, at least. It's as dead
> as the XR2206, though.
>
> You can drive the '555 reference, but that's a tad messy.
>
> So, what IS still available that's near ideal, in IC form?
> Three resistors, a TL431, a dual comparator and an R/S flop
> would be more messy.
>

An RRO comparator such as a TLV7031 and two resistors. Run the op amp
off an LP2951 to get decent rails.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Re: If you want an accurate Schmitt function, rather than a fast one...

<47372594-1b17-9a4d-2430-2fcea5dd55be@electrooptical.net>

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From: pcdhSpam...@electrooptical.net (Phil Hobbs)
Newsgroups: sci.electronics.design
Subject: Re: If you want an accurate Schmitt function, rather than a fast
one...
Date: Thu, 13 Jan 2022 11:42:13 -0500
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 by: Phil Hobbs - Thu, 13 Jan 2022 16:42 UTC

Phil Hobbs wrote:
> whit3rd wrote:
>> what do you use?
>>
>> I want to know the high and low switch thresholds, precisely,
>> and for them  not to drift.
>>
>> A '555 relies on its power rails for thresholds, and an op amp
>> needs rail/rail output for the positive feedback to be accurate,
>> neither of which is ideal for a timing component.
>> The old LM322 had a regulator, at least.   It's as dead
>> as the XR2206, though.
>>
>> You can drive the '555 reference, but that's a tad messy.
>>
>> So, what IS still available that's near ideal, in IC form?
>> Three resistors, a TL431, a dual comparator and an R/S flop
>> would be more messy.
>>
>
> An RRO comparator such as a TLV7031 and two resistors.  Run the

comparator
> off an LP2951 to get decent rails.
>
> Cheers
>
> Phil Hobbs
>

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

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