Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Phil Hobbs Newsgroups: sci.electronics.design Subject: Re: An actual circuit Date: Sat, 25 May 2024 00:45:31 -0000 (UTC) Organization: A noiseless patient Spider Lines: 153 Message-ID: References: <1cv15jdls60tjfcndqe9qm7bgjdtchv9u9@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Injection-Date: Sat, 25 May 2024 02:45:32 +0200 (CEST) Injection-Info: dont-email.me; posting-host="0f741b375bb12ae64014156dc1b373b1"; logging-data="2699690"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+Ikf7W7My2Iny0pk83TWda" User-Agent: NewsTap/5.5 (iPhone/iPod Touch) Cancel-Lock: sha1:YlY8zRsWiuxcBkYKph92ZDW9d5w= sha1:BSiVfPK84VoptfNB6fVd0foAfVs= Bytes: 7272 john larkin wrote: > 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. 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