Path: ...!weretis.net!feeder9.news.weretis.net!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 19:06:50 -0400 Organization: BWH Usenet Archive (https://usenet.blueworldhosting.com) Lines: 162 Message-ID: References: <1cv15jdls60tjfcndqe9qm7bgjdtchv9u9@4ax.com> Injection-Date: Fri, 24 May 2024 23:06:51 -0000 (UTC) Injection-Info: nnrp.usenet.blueworldhosting.com; logging-data="81837"; mail-complaints-to="usenet@blueworldhosting.com" Cancel-Lock: sha1:4mBi1o4IsLY0kNfZyKzXGGCytGc= sha256:YrYwl0NKCqRhxIr07uvd+UC/VcKXqg8YhT9f2I92uBo= sha1:3VXO7xGu1CKOYWjrVKRM3SUAy+g= sha256:g/91zUr5ew604wlzi+vYHp4gY7FPLNSAGMnahqJEgiA= X-RFC2646: Format=Flowed; Original X-MSMail-Priority: Normal X-Priority: 3 X-Newsreader: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 Bytes: 7173 "Phil Hobbs" wrote in message news:v2r4od$2h9gp$1@dont-email.me... > 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. >> > > Oh, I haven't etched a PCB in forty-odd years. This is strictly dead-bug > stuff. 47 years ago in my case when I made an external keyboard because the one supplied by Sinclair was useless. https://en.wikipedia.org/wiki/MK14 > > Cheers > > Phil Hobbs > > > -- > Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC > / > Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics