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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: An actual circuit
Date: Fri, 24 May 2024 23:19:03 -0400
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"john larkin" <jl@650pot.com> wrote in message 
news:phk15jlc055d4p4b1qlicodl16v85u00d9@4ax.com...
> On Fri, 24 May 2024 11:59:31 -0400, "Edward Rawde"
> <invalid@invalid.invalid> wrote:
>
>>"john larkin" <jl@650pot.com> wrote in message
>>news:bk815jh3skuecf1tap8o41rpgdh5kkq8o5@4ax.com...
>>> On Thu, 23 May 2024 13:06:46 -0700, john larkin <jl@650pot.com> wrote:
>>>
>>>>On Thu, 23 May 2024 15:35:00 -0400, "Edward Rawde"
>>>><invalid@invalid.invalid> wrote:
>>>>
>>>>>I was having a conversation with a younger person who seemed to be of 
>>>>>the
>>>>>view that to make an LED flash you would need something to decide when 
>>>>>it
>>>>>should be on or off. So that would be some kind of software or digital
>>>>>system.
....
>>
>>If R2 and R6 are both 3.3k then LTSpice says it slowly drifts into 
>>operation
>>after 40 seconds.
>>But why does it go one way and not the other?
>>Is that an artefact of asymmetry in the simulation?
>>Or is there some hidden asymmetry in the circuit I'm not seeing when R2 is
>>3.3k?
>>
>
> Yes, it is mysterious. Set both drain resistors to 3.3K and zoom way
> up on the two source voltages for the first 20 seconds.

Why the crossover at 15 seconds?
I think reliable startup of the simulated symmetrical version has to be a 
simulation artefact.

Now I'm curious what the real circuit would do.
I may have suitable parts.

>
> LT Spice may have some hidden asymmetry. It has to do math
> sequentially, maybe.
>
> In real life, parts will be plenty asymmetric. Especially jfets.
>