Reply by October 20, 20142014-10-20
On Monday, October 20, 2014 4:00:56 AM UTC+1, Bill Bowden wrote:
> <meow2222@care2.com> wrote in message > news:e26709e0-9ecc-4465-a217-a125a0f9fff9@googlegroups.com... > > On Saturday, October 18, 2014 9:44:24 PM UTC+1, meow...@care2.com wrote: > >> On Saturday, October 18, 2014 12:10:47 AM UTC+1, meow...@care2.com wrote:
> >> > Hi folks. I'm looking to choose a couple of oscillators for 3rd world > >> > construction/use, and I'm very rusty on the properties of the numerous > >> > options. What's essential: > >> > - reasonably frequency stable with quite widely varying psu voltage, eg > >> > 5-9v > >> > - discrete parts only, ICs can't be counted on to be available > >> > - common parts only, no tapped inductors etc > >> > - the minimum of parts is a major choice factor > >> > Plusses would be: > >> > no inductors > >> > npn trs only > >> > The prime app is as a sig-gen. Frequncy range etc are determined more > >> > by BOM than anything else, its down to what can we manage with a few > >> > cheap parts. (I've used opamps for basic miniature pocket use sig gens, > >> > but can't do that here.) > >> > A 2nd app for an LED strobe might also be handy. This would need a > >> > mark/space of 10:1 or so to get decent clarity of speed measurements. > >> > Again its a question of what can we do at minimum cost. > >> > thank you, NT
> >> OK, I got spicy.... > > > >> But its suffering problems, and I'm not seeing why.
> > Have played with a multivibrator, and as someone suggested its pretty much > > bulletproof. Just the job! Thankyou everyone.
> Try a darlington for Q1 or add another 2N2222 so the emitter of the second > drives the base of the first.
I wondered about that, or adding an output stage so loading doesnt affect the osc. But once there are 2 trs, the multivibrator makes more sense.
> It will drive 50 ohms but it's a little > distorted and clipped at the bottom. You could lower R4 to 25 ohms and get a > cleaner sine wave, but the circuit would draw 140 mA.
Yes, but not compatible with running it off flat batteries found thrown out. Also would consume batteries much quicker. Everything's a tradeoff. NT
Reply by Bill Bowden October 20, 20142014-10-20
<meow2222@care2.com> wrote in message 
news:e26709e0-9ecc-4465-a217-a125a0f9fff9@googlegroups.com...
> On Saturday, October 18, 2014 9:44:24 PM UTC+1, meow...@care2.com wrote: >> On Saturday, October 18, 2014 12:10:47 AM UTC+1, meow...@care2.com wrote: >> > Hi folks. I'm looking to choose a couple of oscillators for 3rd world >> > construction/use, and I'm very rusty on the properties of the numerous >> > options. What's essential: >> > - reasonably frequency stable with quite widely varying psu voltage, eg >> > 5-9v >> > - discrete parts only, ICs can't be counted on to be available >> > - common parts only, no tapped inductors etc >> > - the minimum of parts is a major choice factor >> > Plusses would be: >> > no inductors >> > npn trs only >> > The prime app is as a sig-gen. Frequncy range etc are determined more >> > by BOM than anything else, its down to what can we manage with a few >> > cheap parts. (I've used opamps for basic miniature pocket use sig gens, >> > but can't do that here.) >> > A 2nd app for an LED strobe might also be handy. This would need a >> > mark/space of 10:1 or so to get decent clarity of speed measurements. >> > Again its a question of what can we do at minimum cost. >> > thank you, NT > >> OK, I got spicy.... > >> But its suffering problems, and I'm not seeing why. > > Have played with a multivibrator, and as someone suggested its pretty much > bulletproof. Just the job! Thankyou everyone. > > > NT
Try a darlington for Q1 or add another 2N2222 so the emitter of the second drives the base of the first. It will drive 50 ohms but it's a little distorted and clipped at the bottom. You could lower R4 to 25 ohms and get a cleaner sine wave, but the circuit would draw 140 mA. --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
Reply by David Eather October 19, 20142014-10-19
On Mon, 20 Oct 2014 06:06:41 +1000, <meow2222@care2.com> wrote:

> On Sunday, October 19, 2014 8:34:06 PM UTC+1, David Eather wrote: >> On Sun, 19 Oct 2014 05:50:21 +1000, <meow2222@care2.com> wrote: > >> > I assume they're marked BC547 because they meet all the specs, so >> should >> > be fine for all the usual apps. > >> That is the million dollar question. > > Why is it a question? > > > NT
Because I don't know if they meet all specs. If you screw up the doping what else changes.
Reply by October 19, 20142014-10-19
On Sunday, October 19, 2014 8:34:06 PM UTC+1, David Eather wrote:
> On Sun, 19 Oct 2014 05:50:21 +1000, <meow2222@care2.com> wrote:
> > I assume they're marked BC547 because they meet all the specs, so should > > be fine for all the usual apps.
> That is the million dollar question.
Why is it a question? NT
Reply by David Eather October 19, 20142014-10-19
On Sun, 19 Oct 2014 05:50:21 +1000, <meow2222@care2.com> wrote:

> On Saturday, October 18, 2014 6:26:02 PM UTC+1, David Eather wrote: >> On Sun, 19 Oct 2014 02:12:42 +1000, Tim Wescott <tim@seemywebsite.com> >> wrote: >> > On Sat, 18 Oct 2014 06:10:29 -0700, meow2222 wrote: >> >> On Saturday, October 18, 2014 2:30:27 AM UTC+1, Tim Wescott wrote: >> >>> On Fri, 17 Oct 2014 16:10:47 -0700, meow2222 wrote: > >> >>> > Hi folks. I'm looking to choose a couple of oscillators for 3rd >> world >> >>> > construction/use, and I'm very rusty on the properties of the >> >>> > numerous options. What's essential: >> >>> > - reasonably frequency stable with quite widely varying psu >> voltage, >> >>> > eg 5-9v - discrete parts only, ICs can't be counted on to be >> >>> > available - common parts only, no tapped inductors etc - the >> minimum >> >>> > of parts is a major choice factor >> >>> > > Plusses would be: >> >>> > no inductors npn trs only >> >>> > > The prime app is as a sig-gen. Frequncy range etc are determined >> >>> > > more by >> >>> > BOM than anything else, its down to what can we manage with a few >> >>> > cheap parts. (I've used opamps for basic miniature pocket use sig >> >>> > gens, but can't do that here.) >> >>> > > A 2nd app for an LED strobe might also be handy. This would >> need a >> >>> > mark/space of 10:1 or so to get decent clarity of speed >> measurements. >> >>> > Again its a question of what can we do at minimum cost. >> >>> > > > thank you, NT >> >> >> >>> It's cool that you're working on this. >> >>> I'd suggest that if you're going to be doing much of this, that you >> >>> start collecting electronics and amateur radio magazines from the >> >>> 1960's and '70's. There should be a rich supply there. >> >> >> >> Interesting. >> >> >> >>> You can make a reasonably stable 6V-ish zener from a reverse-biased >> BE >> >>> junction on a 2N2222-ish transistor. Then use that as a reference >> for >> >>> a regulated supply. >> >> >> >> Does that trick work with almost any npn tr? Its impractical to >> specify >> >> specific trs, but no problem to say 'this size npn.' Zeners should be >> >> available too, but its potluck what the voltages would be. >> > >> > It works with all the small-signal ones that I've tried. I think >> it's a >> > direct consequence of the doping profiles you need to get good >> transistor >> > action -- but I don't know. > >> I've got a bunch of BC547B's (jelly bean type npn with gain of 400) and >> they all zener (rBE) at just shy of 9v - I was wondering if I should >> post >> about them and ask if anyone has seen similar and what might be the >> other >> consequences of using these strange beasts. Normally(?) a BC547 zeners >> at >> 5-6 volts. > > I assume they're marked BC547 because they meet all the specs, so should > be fine for all the usual apps.
That is the million dollar question.
Reply by October 19, 20142014-10-19
On Saturday, October 18, 2014 9:44:24 PM UTC+1, meow...@care2.com wrote:
> On Saturday, October 18, 2014 12:10:47 AM UTC+1, meow...@care2.com wrote: > > Hi folks. I'm looking to choose a couple of oscillators for 3rd world construction/use, and I'm very rusty on the properties of the numerous options. What's essential: > > - reasonably frequency stable with quite widely varying psu voltage, eg 5-9v > > - discrete parts only, ICs can't be counted on to be available > > - common parts only, no tapped inductors etc > > - the minimum of parts is a major choice factor > > Plusses would be: > > no inductors > > npn trs only > > The prime app is as a sig-gen. Frequncy range etc are determined more by BOM than anything else, its down to what can we manage with a few cheap parts. (I've used opamps for basic miniature pocket use sig gens, but can't do that here.) > > A 2nd app for an LED strobe might also be handy. This would need a mark/space of 10:1 or so to get decent clarity of speed measurements. Again its a question of what can we do at minimum cost. > > thank you, NT
> OK, I got spicy....
> But its suffering problems, and I'm not seeing why.
Have played with a multivibrator, and as someone suggested its pretty much bulletproof. Just the job! Thankyou everyone. NT
Reply by John S October 19, 20142014-10-19
On 10/19/2014 7:35 AM, meow2222@care2.com wrote:
> On Sunday, October 19, 2014 12:11:11 PM UTC+1, John S wrote: >> On 10/18/2014 3:44 PM, meow2222@care2.com wrote: > >>> But its suffering problems, and I'm not seeing why. The quiescent >>> point & amplitude are rather low, and no tweak of R values seems >>> to fix either - in fact most such tweaks result in oscillation >>> failing entirely. Ditto raising Vcc. Drop Rout to 1k and it fails >>> to oscillate. I'm missing something here... what? >>> >>> Haven't added battery R yet, will do that later. Just want to get >>> a key issue fixed first.
The battery R is 330 ohms.
>> The circuit can't drive a 1 ohm load. > > Rout is 10k, so its driving 10k. much less and it stops oscillating.
Yes, so Rout is now 1K when you change it and complain. The feedback from collector back through the net into the base is insufficient to maintain oscillation when you load the collector that much.
> It needs to at least keep oscillating with any load, hence the 1 ohm > test load.
Fine, so leave Rout high enough to continue oscillating. You have no other choice with all the other constraints you have imposed. It seems there's not much gain margin, as all sorts of
> tweaks result in oscillation failure. So I'll try the multivibrator. > > > NT >
Reply by Bill Sloman October 19, 20142014-10-19
On Sunday, 19 October 2014 14:37:52 UTC+11, Robert Baer  wrote:
> Tim Wescott wrote: > > On Fri, 17 Oct 2014 16:10:47 -0700, meow2222 wrote=20
<snip>
> Well, almost all transistors zener in the 8-9V region; doubt the =20 > 2N2222 is that different.
Gold-doped switching transistor tend to zener around 5.6V, where the temper= ature coefficient of break-down voltage is about 2mV/C . If you exploit the= collector-base diode as a forward diode in series with the reverse-based b= ase-emitter junction you getting something very close to Motorola's 1N821 = - 1N829 series of nominally 6.2V reference diodes. The zero-temperature coe= fficient current isn't 7.5mA, but somewhere around a few mA. Back in the 1960's there was a paper in the UK Journal of Scientific Instru= ments (now Measurement Science and Technology) which spelled out how to use= a popular gold-doped switching transistor - probably the 2N2369 - instead = something out of the 1N821-9 series. It could be this paper http://iopscience.iop.org/0950-7671/39/2/428 --=20 Bill Sloman, Sydney
Reply by October 19, 20142014-10-19
On Sunday, October 19, 2014 12:11:11 PM UTC+1, John S wrote:
> On 10/18/2014 3:44 PM, meow2222@care2.com wrote:
> > But its suffering problems, and I'm not seeing why. The quiescent point=
& amplitude are rather low, and no tweak of R values seems to fix either -= in fact most such tweaks result in oscillation failing entirely. Ditto rai= sing Vcc. Drop Rout to 1k and it fails to oscillate. I'm missing something = here... what?
> > > > Haven't added battery R yet, will do that later. Just want to get a key=
issue fixed first.
> The circuit can't drive a 1 ohm load.
Rout is 10k, so its driving 10k. much less and it stops oscillating. It nee= ds to at least keep oscillating with any load, hence the 1 ohm test load. I= t seems there's not much gain margin, as all sorts of tweaks result in osci= llation failure. So I'll try the multivibrator. NT
Reply by John S October 19, 20142014-10-19
On 10/18/2014 3:44 PM, meow2222@care2.com wrote:
> On Saturday, October 18, 2014 12:10:47 AM UTC+1, meow...@care2.com wrote: > >> Hi folks. I'm looking to choose a couple of oscillators for 3rd world construction/use, and I'm very rusty on the properties of the numerous options. What's essential: >> - reasonably frequency stable with quite widely varying psu voltage, eg 5-9v >> - discrete parts only, ICs can't be counted on to be available >> - common parts only, no tapped inductors etc >> - the minimum of parts is a major choice factor >> Plusses would be: >> no inductors >> npn trs only >> The prime app is as a sig-gen. Frequncy range etc are determined more by BOM than anything else, its down to what can we manage with a few cheap parts. (I've used opamps for basic miniature pocket use sig gens, but can't do that here.) >> A 2nd app for an LED strobe might also be handy. This would need a mark/space of 10:1 or so to get decent clarity of speed measurements. Again its a question of what can we do at minimum cost. >> thank you, NT > > > OK, I got spicy.... > > Version 4
(snip)
> > But its suffering problems, and I'm not seeing why. The quiescent point & amplitude are rather low, and no tweak of R values seems to fix either - in fact most such tweaks result in oscillation failing entirely. Ditto raising Vcc. Drop Rout to 1k and it fails to oscillate. I'm missing something here... what? > > Haven't added battery R yet, will do that later. Just want to get a key issue fixed first. > > > NT
The circuit can't drive a 1 ohm load.