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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: An actual circuit
Date: Fri, 24 May 2024 13:56:49 -0700
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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.