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From: Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>
Newsgroups: sci.electronics.design
Subject: Re: An actual circuit
Date: Sat, 25 May 2024 00:45:31 -0000 (UTC)
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john larkin <jl@650pot.com> wrote:
> On Fri, 24 May 2024 22:35:57 -0000 (UTC), Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
> 
>> Edward Rawde <invalid@invalid.invalid> wrote:
>>> "Phil Hobbs" <pcdhSpamMeSenseless@electrooptical.net> wrote in message 
>>> news:v2r325$2h00c$1@dont-email.me...
>>>> john larkin <jl@650pot.com> wrote:
>>>>> On Fri, 24 May 2024 16:22:23 -0400, "Edward Rawde"
>>>>> <invalid@invalid.invalid> wrote:
>>>>> 
>>>>>> "john larkin" <jl@650pot.com> wrote in message
>>>>>> news:uts15jlh0oo1hin58uu4a574kg5q3j9q5b@4ax.com...
>>>>>>> On Fri, 24 May 2024 14:50:19 -0400, "Edward Rawde"
>>>>>>> <invalid@invalid.invalid> wrote:
>>>>>>> 
>>>>>>>> "Jeroen Belleman" <jeroen@nospam.please> wrote in message
>>>>>>>> news:v2qmeq$2eknc$1@dont-email.me...
>>>>>>>>> On 5/24/24 17:59, Edward Rawde 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.
>>>>>>>>>> ...
>>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> The classic NPN astable circuit can hang up, with both transistors
>>>>>>>>>>> saturated. I wonder if he jfet circuit can hang too, with Idss
>>>>>>>>>>> grounding both drains and not enough gain to oscillate out of that
>>>>>>>>>>> state.
>>>>>>>>>>> 
>>>>>>>>>>> Even when they have a hang state, luck usually kicks them off into
>>>>>>>>>>> oscillation. Your source resistors and  asymmetric drain resistors
>>>>>>>>>>> help it start up. Try making both drain resistors 3.3K.
>>>>>>>>>>> 
>>>>>>>>>>> If you make the source resistors lower, it will hang up.
>>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> Yes I noticed both points when I was designing it.
>>>>>>>>>> I wanted to have it start up by itself, preferably without a 
>>>>>>>>>> kickstart
>>>>>>>>>> capacitor.
>>>>>>>>>> So I had a complicated circuit with two more diodes and a transistor 
>>>>>>>>>> in
>>>>>>>>>> the
>>>>>>>>>> hope that I could detect the hang state and force it off balance.
>>>>>>>>>> I couldn't get that to work
>>>>>>>>>> Then I accidentally made R2 3,3k and R6 3.3k and I didn't see how it
>>>>>>>>>> could
>>>>>>>>>> start so quickly with no other help.
>>>>>>>>>> Eventually I noticed 3,3k which maybe LTSpice takes as 3k.
>>>>>>>>>> 
>>>>>>>>>> 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?
>>>>>>>>> 
>>>>>>>>> Below are a pair of astable circuits. The left one is like yours,
>>>>>>>>> with a hangup state. I start it by specifying an initial condition.
>>>>>>>>> The right one will start all by itself.
>>>>>>>>> 
>>>>>>>> 
>>>>>>>> Thanks for that. I guess I'm biased towards components I could easily 
>>>>>>>> get
>>>>>>>> in
>>>>>>>> the 70s. And also through hole components I can easily build a real
>>>>>>>> circuit
>>>>>>>> with.
>>>>>>>> 
>>>>>>>> 
>>>>>>> 
>>>>>>> I like to use surface-mount parts on a Dremeled PCB.
>>>>>>> 
>>>>>>> https://www.dropbox.com/s/7bihbjbaojvta0z/Z382_1.JPG?raw=1
>>>>>>> 
>>>>>>> https://www.dropbox.com/s/zaftysxtgclxj82/Z412_Proto.JPG?raw=1
>>>>>>> 
>>>>>>> You can do fast, 50-ohm picosecond stuff this way too.
>>>>>>> 
>>>>>> 
>>>>>> Thanks I probably do have some copper clad board I could do that with.
>>>>>>> 
>>>>>> 
>>>>> 
>>>>> Use a round-end carbide dental burr. They are cheap on ebay.
>>>>> 
>>>>> It's cool, kind of an art form. Takes some practice.
>>>>> 
>>>>> I have a few square feet of gold-plated copperclad FR4, which is even
>>>>> nicer. Regular copperclad looks grungy after a few months.
>>>>> 
>>>>> 
>>>> 
>>>> I'm not nearly as posh as you are
>>> 
>>> Not sure why that made me laugh.
>>> 
>>>> , so for my purposes a spritz of Krylon
>>>> clear acrylic on a clean board is a ticket.
>>>> 
>>>> You can solder right through it, and it keeps the copper looking nice for 
>>>> a
>>>> long time.
>>> 
>>> I seem to remember, a long long time ago using copper clad board, some clear 
>>> sticky tape and a very sharp knife.
>>> Followed by Ferric Chloride.
>>> An etch resist pen could also be used if the tape removal didn't go exactly 
>>> as planned.
>>> 
>>> But yes it's true that after removing the etch resist you might want 
>>> something to keep the copper looking nice and shiny.
> 
> Soft Scrub. It's basically an optical polish.

I generally use Barkeeper’s Friend on a damp paper towel. (That’s what’s
under the bathroom sink at the lab. )

>> Oh, I haven’t etched a PCB in forty-odd years. This is strictly dead-bug
>> stuff. 
>> 
> 
> Insect cruelty. Plus you have to count their tiny feets backwards.

The only good bugs is dead bugs. ;)
> 
Cheers 

Phil Hobbs 


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