Path: ...!Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Fri, 24 May 2024 23:59:58 +0000 From: john larkin Newsgroups: sci.electronics.design Subject: Re: An actual circuit Date: Fri, 24 May 2024 16:59:58 -0700 Message-ID: References: <1cv15jdls60tjfcndqe9qm7bgjdtchv9u9@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Lines: 146 X-Trace: sv3-Yjy25Q/7lcrmZ4RdBAjOeog9zXNKcSTymNX6ubUciHKXCb8G8OLpFbNpvN2D7lhvwJf2nBSD0XJgjf+!7J2EQ34FvD1BGDuf7tME07zXafd2BC7Xb5RilunRlZ3rly06B72KOloNm8gyg+DOBpqShHYF41xT!U55Rhg== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 6723 On Fri, 24 May 2024 22:35:57 -0000 (UTC), Phil Hobbs wrote: >Edward Rawde wrote: >> "Phil Hobbs" wrote in message >> news:v2r325$2h00c$1@dont-email.me... >>> john larkin wrote: >>>> On Fri, 24 May 2024 16:22:23 -0400, "Edward Rawde" >>>> wrote: >>>> >>>>> "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. >>>>>> >>>>> >>>> >>>> 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. >> > >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. >Cheers > >Phil Hobbs