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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!news.misty.com!weretis.net!feeder9.news.weretis.net!panix!usenet.blueworldhosting.com!diablo1.usenet.blueworldhosting.com!nnrp.usenet.blueworldhosting.com!.POSTED!not-for-mail From: "Edward Rawde" Newsgroups: sci.electronics.design Subject: Re: An actual circuit Date: Fri, 24 May 2024 16:22:23 -0400 Organization: BWH Usenet Archive (https://usenet.blueworldhosting.com) Lines: 86 Message-ID: References: Injection-Date: Fri, 24 May 2024 20:22:25 -0000 (UTC) Injection-Info: nnrp.usenet.blueworldhosting.com; logging-data="23936"; mail-complaints-to="usenet@blueworldhosting.com" Cancel-Lock: sha1:wk7ZvM9ZBaUK1GT5Y4yyuqrUEsU= sha256:qB1Bea7XTYJQqDVNqFrKe8dghIOKV33TUyuISj74eLU= sha1:ElfT51UQi3afICc4rt1rTKQgVDE= sha256:Yud70nBTyxmBMxpo255r5I1Hl284RJH8Te+EAqqePb4= X-MSMail-Priority: Normal X-Priority: 3 X-RFC2646: Format=Flowed; Original X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 Bytes: 4520 "john larkin" wrote in message news:uts15jlh0oo1hin58uu4a574kg5q3j9q5b@4ax.com... > On Fri, 24 May 2024 14:50:19 -0400, "Edward Rawde" > wrote: > >>"Jeroen Belleman" wrote in message >>news:v2qmeq$2eknc$1@dont-email.me... >>> On 5/24/24 17:59, Edward Rawde wrote: >>>> "john larkin" wrote in message >>>> news:bk815jh3skuecf1tap8o41rpgdh5kkq8o5@4ax.com... >>>>> On Thu, 23 May 2024 13:06:46 -0700, john larkin wrote: >>>>> >>>>>> On Thu, 23 May 2024 15:35:00 -0400, "Edward Rawde" >>>>>> 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. >