Which oscillator?

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.

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.

Do you just need a wiggly line on a scope, do you need square waves, triangle waves, sine waves, what?

Why not just whistle into a speaker or earbud? Or fit a tuning fork with a magnet and a coil of wire?

A two transistor multivibrator might be a good choice if you don't need to go to very high frequencies and you don't need a sine wave output. For audio and low rf, almost any npn transistors will work. From what I remember of building these with salvaged transistors a very long time ago they are very forgiving circuits. The output is a square wave or pulse train depending on component values. The frequency does vary a bit with supply voltage. However, the circuit "just works" with almost any components and has no inductors or anything else special. Frequency can be tuned by varying one of the resistors giving a variable repetition rate pulse train.

John

On a sunny day (Fri, 17 Oct 2014 16:10:47 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

mm that last thing... I got a lot of UJTs from ebay a while back. Simpler is hard.

I showed a LED strobe with one here a while back.

by

Interesting.

Does that trick work with almost any npn tr? Its impractical to specify spe cific trs, but no problem to say 'this size npn.' Zeners should be availabl e too, but its potluck what the voltages would be.

It would be a real plus to be able to calibrate the frequency dial and/or s witching, and have it stay on target regardless of how many cells it runs o ff, or how flat they are.

Basically want a pocket tool thats useful to people learning and doing elec tronics in its various forms. So I guess there's room for minimal and more capable kit. I'm looking to start with something minimal as its quicker to design & write up, and quicker & cheaper to build, thus can benefit more pe ople. So for the first version, pretty much any wave would be of use.

NT

onstruction/use, and I'm very rusty on the properties of the numerous optio ns. What's essential:

That's 1 of the 2 possibles I've looked at. The main downside is the need t o change at least 2 component values to vary frequency, and practically 4. A ganged VR could change frequency over 10:1, but to shift decade would mea n switching 2 caps. And there is the varying with Vcc, but realistically I think that's going to happen with any basic 1 or 2 tr oscillator.

The other one I looked at is 1 tr with RCRC feedback. Again multiple value changes needed to change frequency, and the load would affect freq too. But its certainly basic, with just 1 tr. But the switching isn't.

NT

The need for a UJT would much reduce the ability to build the things. A UJT LED strobe does sound interestingly minimal, but I'm not convinced its practical due to the shortage of UJTs in scrap appliances.

NT

On a sunny day (Sat, 18 Oct 2014 06:51:56 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

Its probably cheaper to buy 100 UJTs on ebay than to get all that scrap, look for usable NPNs, get those out.. etc. I've build things from scrap PCBs, these days maybe the resitors are marked, but the capacitiors wont be, its all SMD, the transistors wont be marked either. Now you need a C and ohm meter too.

Depends a bit how old the scrap is. With modern SMD parts you can do cheaper with new, all you need is a soldering iron and a pair of pliers. Its not like an SMD resistor or capacitor is expensive. Then better buy for 10$ parts, and they can make a hundred of these things and get hands on feeling with SMD. Veroboard.

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 learned it from some ham radio electronics book or another.

I think that to start you want some sort of multivibrator, and you want to pull in your horns on stability and accuracy.

construction/use, and I'm very rusty on the properties

eg 5-9v

UJT LED strobe does sound interestingly minimal, but I'm

ces.

SMD.

This is primarily for people stuck in poverty rather than established busin esses. So fancy things like new parts, veroboard, electric irons etc are ou t of the question. Electronic scrap is found by the roadside and at tips. S oldering can be done with a nail, and a pointed screw works well for removi ng through hole parts.

For now I want to get as much bang for as little buck as possible, using ci rcuits that can be made from the widest possible range of tron scrap.

NT

On a sunny day (Sat, 18 Oct 2014 09:44:37 -0700 (PDT)) it happened snipped-for-privacy@care2.com wrote in :

I admire your good intentions, as a kid I have soldered with a screwdriver heated in the coal fireplace. Parts were a LOT bigger then, no transistors... The soldering was not reall reliable, no flux... :-) S39 flux (what plumbers use here) killed capacitors..

So somebody is going to go there and teach those kids or people how to do that. If it is you I would spend that same amount you spend on travel expenses on some electronics kits or ebay parts. Reality. They would have to know about that anyways if it is for their future. It would be a 'holding hand' lesson, with a million questions. I would donate the parts, that cost would be nothing compared to the cost of time and travel. If they can read they could use a good book on the subject as guide too.

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

you can use sensitive gate SCR's and make oscillators, so it isn't a horrible deal if UJT become in short supply..

Jamie

Thanks, handy to know

NT

I guess that's inevitably true. How can one have a fixed Vbe threshold plus variable Vcc, yet get consistent timing. I don't want to waste parts & battery power on a regulator stage.... unless I just zener regulate the feedback path?

Multivibrator:

RCRC osc:

Looks like the latter wins, unless it runs into some problem down the line. I think its spice time.

NT

I assume they're marked BC547 because they meet all the specs, so should be fine for all the usual apps. Unless I'm mistaken, Veb spec is a min figure. Only if you rely on Veb breakdown are you into not-fully specified territory.

NT

...

No. Once the circuit is worked out, it will go into a booklet that explains how to do it. Other booklets in the series will explain other aspects of things.

Books are the only real option when its to be accessible to over a billion people. I learnt electronics from books, for most of us there was no internet.

These will also go online for people that can access it. There its practical to include a FAQ, links to related info etc.

NT

struction/use, and I'm very rusty on the properties of the numerous options . What's essential:

-9v

BOM than anything else, its down to what can we manage with a few cheap par ts. (I've used opamps for basic miniature pocket use sig gens, but can't do that here.)

pace of 10:1 or so to get decent clarity of speed measurements. Again its a question of what can we do at minimum cost.

OK, I got spicy....

Version 4 SHEET 1 880 680 WIRE -400 -48 -480 -48 WIRE 128 -48 -400 -48 WIRE -480 -32 -480 -48 WIRE -400 -16 -400 -48 WIRE 128 -16 128 -48 WIRE -480 64 -480 48 WIRE -400 64 -400 48 WIRE 128 80 128 64 WIRE 128 80 -640 80 WIRE 208 80 128 80 WIRE 336 80 288 80 WIRE 416 80 400 80 WIRE 416 208 416 80 WIRE -640 240 -640 80 WIRE -512 240 -560 240 WIRE -448 240 -512 240 WIRE -304 240 -368 240 WIRE -256 240 -304 240 WIRE -128 240 -176 240 WIRE 64 240 -128 240 WIRE 128 256 128 80 WIRE -512 288 -512 240 WIRE -304 288 -304 240 WIRE -128 288 -128 240 WIRE 64 304 64 240 WIRE -512 400 -512 352 WIRE -304 400 -304 352 WIRE -304 400 -512 400 WIRE -128 400 -128 352 WIRE -128 400 -304 400 WIRE -48 400 -128 400 WIRE 128 400 128 352 WIRE 128 400 -48 400 WIRE 416 400 416 288 WIRE 416 400 128 400 WIRE -48 432 -48 400 FLAG -480 64 0 FLAG -48 432 0 FLAG -400 64 0 SYMBOL npn 64 256 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL voltage -480 -48 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL res 112 -32 R0 SYMATTR InstName R4 SYMATTR Value 330 SYMBOL cap -416 -16 R0 SYMATTR InstName C1

SYMBOL res -160 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -352 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL cap -320 288 R0 SYMATTR InstName C2

SYMBOL cap -144 288 R0 SYMATTR InstName C3

SYMBOL cap -528 288 R0 SYMATTR InstName C4

SYMBOL res -544 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res 304 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName Rout SYMATTR Value 10k SYMBOL cap 400 64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName Cout

SYMBOL res 400 192 R0 SYMATTR InstName Rload SYMATTR Value 1 TEXT -512 -88 Left 2 !.tran 0 1 0 10u startup

But its suffering problems, and I'm not seeing why. The quiescent point & a mplitude 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 iss ue fixed first.

NT

Phase retard oscillator: R, C, Q; collector waveform tends to be square wave, and base waveform tends to be sine (at reduced amplitude). Been ages, think min gain for oscillation is 29.