[sdiy] Schmitt Trigger Questions

[Scott Gravenhorst]

harrybissell <harrybissell at prodigy.net> wrote:
>Ok a sort of answer...
>
>the CMOS schmitt triggers give you NO control over the thresholds...

Actually, that's not entirely true.  You are probably referring to built in ST
stuff like the clock conditioning input circuit of a 4027, or schitt trigger
gates.  I'm talking about using two CMOS inverters with an input resistor and a
feedback resistor.  Take a look at the data sheet for a 4069UB, the schematic
with programming maths are there.

>they are quite fast but they vary from unit to unit and VERY (vary) from
>manufacturer to manufacturer.

Given, but I'm not really considering using them.

>
>I remember one chip (national imho) where the schmitt trigger input to
>a counter was the SECOND stage... so a slow moving input would get
>trashed by the first stage, then the trash would be squared up by the
>schmitt trigger. VERY dumb... I only hope it was to avoid a patent and not
>just sheer stupidity. Imagine how well THAT worked when they switched to that
>chip in production...

Geeziz crap unmighty...

>
>H^) harry
>
>Scott Gravenhorst wrote:
>
>> The discussion of the 3080 schmitt trigger induces a question or two:
>>
>> Can anyone comment on a comparison between the 3080 and LM13x00 OTA schmitt
>> triggers?
>>
>> What about CMOS inverter based schmitt triggers?
>>
>> 4069UB and 4007UB show a 30 or 40 nanosecond propagation delay (10 volts)
>> in general, but there's nothing given about a schmitt trigger arrangement.
>>  Are these as fast, faster or slower than OTAs when used as schmitt triggers?
>>
>> ---------------------------------------------------------
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>> -- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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>

---------------------------------------------------------
- Where merit is not rewarded, excellence fades.
- Hydrogen is pointless without solar.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- The only good terrorist is a dead terrorist.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/FatMan/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- Autodidactic Master of Arcane and Hidden Knowledge.