Make a very simple test for me

_q12x_ · May 15, 2022

Im asking this question to everyone but in particular to my friend here mister @marconi .
I am a professional artist but I am not an electronist like you guys here. That doesnt mean I dont know anything. I know something but I can't raise to some of your standards and knowledge. I'm happy (sometimes fun) to learn something new here and there.
- Recently, it was suggested to me to buy a frequency counter, because I got into some crystal oscillators I have in my stock and they have no markings anymore and the reason is a bit too long story. I already buy a cheap one from ebay, exactly this yellow version (not the red one)

[ElectriciansForums.net] Make a very simple test for me

but it is on the road. I have about 2-3 months (usually) to wait, until it arrives.
I also have a dinky DSO138 osciloscope that is trembling of Parkinson all the time. So you can imagine, I can't put my 100% trust in it all the time.

So, my first circuit for testing a crystal oscillator I find is this:
"Oscillator Circuit of The First Quartz Wrist Watch"

I had high hopes for this circuit. I used 10k for both Rc(c=collector) and 1k for both Re(e=emitor). And I used BC548 for both Tr.I used a known value of a Quartz of 20MHz. And I used 2V (VB=Voltage Battery). But the oscilloscope just showed me some very weird and random readings that I can not even put head to tail. I build this circuit on my breadboard, and that may had influence the results.

---So this circuit didn't work for me---. But I bet my as it must be a good one and I blame my DSO138 for being crappy.
And also not having (yet) a frequency counter.
- In short, this is more a curiosity for me. I hope it is for you as well.
- My request for you is to help me with the following:
- Because you are a better electronist, you must have better tools than I have. So, using your normal oscilloscope and your normal frequency counter, (I say normal, comparative to my ebay measuring tools), please make this very quick and simple circuit and measure it for me. And confirm to me with some images or a short video, that everything is working as I imagine and hope. It must be. The idea is to measure 20MHz on the "out" pin in respect to the ground (if you used the same values as I used). That's it. Also, feel free to change the resistors or the transistors. It must be GPT (general purpose transistors), but the resistors I used I just guessed their values. I didnt had the values from the page with the circuit. So I had to invent something. And those values are my best guess.
Thank you and hope to hear good news from you.

pc1966 · May 18, 2022

marconi said:
PC1966: I had another try with Rc = 1kR and Re = 4.7kR, 10kR and 22kR over a range of voltages from 3-15V. Not a twitter at 20MHz. I also tried two other crystals.

Next I will try keeping Re at 4.7kR and reducing Rc but at the moment it is too hot in my shed to do so.

OK, I will see if I have the parts to try it as well.

At one point we had loads of stuff for this sort of experiment but sadly it was thrown out when my last work ended. We saved some stuff "just in case" but space did not permit all of the items I wish we had kept.

pc1966 · May 18, 2022

@marconi Was the DC bias condition much as expected? I guess around (Vcc - 0.7) / (Rc + Re) per transistor current, at 5V supply around 3.5V over emitter resistors?

marconi · May 18, 2022

pc1966 said:
@marconi Was the DC bias condition much as expected? I guess around (Vcc - 0.7) / (Rc + Re) per transistor current, at 5V supply around 3.5V over emitter resistors?

I will check tomorrow morning. We are heading for thunder and lightning this evening and it feels very muggy right now.

pc1966 · May 18, 2022

This is a handy web site for current activity:

Lightning & Thunderstorms - United Kingdom, England, Scotland, Wales, Ireland

Blitzortung.org provides lightning and thunderstorm information in real-time on maps for USA, United Kingdom, Australia, new Zealand, Europa, Africa, Asia and other Countries.

www.blitzortung.org

However we have seen the odd flash here that did not register on their detectors.

_q12x_ · May 18, 2022

Im loughing how everyone is preoccupied: me with the fv reading, marconi with lightning and pc1966 with stuff that doesnt find or have anymore. Hahaha.

marconi · May 18, 2022

Regarding the circuit Symmetrischer Oszillator I have included below again. I don't think this is the working circuit - it is an outline schematic of a circuit missing some key detail. I reckon the circuit idea is a classical astable transistor circuit - see second circuit - which has resistance and capacitance to make it oscillate at a frequency close to that of the quartz crystal as in the second image. The purpose of the crystal connected between emitters is to 'force' operation at its frequency. This is what I am going to pursue.

Lucien Nunes · May 18, 2022

I was just going to say, it looks like a circuit from a patent which shows enough to define the principle that is claimed, but not enough to construct a replica directly. I too would be inclined to provide AC feedback and bias in the usual way, and probably make the emitter coupling somewhat tunable.

It seems a very long time ago that I had the opportunity to make with circuits that might not function, to see whether something can be done some particular way. In my work I am so often against time pressure that the solution has to be guaranteed to work first time even it is technically ridiculous or extravagant. I have used a 14-bit 40-pin PIC running at 20MHz as a monostable to generate a 10 second pulse, because it was already built and reprogramming took 2 minutes vs. 5 minutes to make something specific.

If you asked me to test the frequency of a vanilla-flavour crystal now I would reach for the PIC prototyping board again and have an answer in 20 seconds.

_q12x_ · May 18, 2022

We know that is a symbol of a BJT NPN but try with 2 N-ch Mosfets.
Also... Im thinking to use different types of npn's. 1 BC548 and another BD139. To induce a instability in the circuit...
Just putting some ideas on the table.

pc1966 · May 18, 2022

A crude simulation attempt, did not work at 20MHz with 2N2222 but OK with BC548, also used low-Q crystal model so faster to build up (along with 1mV kick at t=0)

Time-domain for test point in Tr1 collector:

Lucien Nunes · May 18, 2022

I gave myself 5 minutes to do this, just to prove we can all build a discrete transistor crystal oscillator that doesn't work...
First transistors I came to - ZTX753s - should have enough zing to work. The circuit has a name but I can't remember it, a common-base stage driving an emitter follower. I made the values up as I went along, they won't be far out but it still doesn't work. I've no interest in simulating it or debugging it, time's up!

Lucien Nunes · May 18, 2022

So then I decided to give myself another 5 minutes to build a crystal oscillator the way I would have done if somebody had said: "Build a simple crystal oscillator." I.e. with an 'HC00. Of course this one works just fine. I didn't bother tuning it, I used the first capacitors that I picked up from the drawer, which turned out to be 22pF. Build time was just under 3 minutes including stripping some wire to make links.

Lucien Nunes · May 18, 2022

And this is how it looks with a 4MHz xtal.

*BONUS POINTS for anyone who noticed I had the scope's 20MHz bandwidth limiting switched on. The actual output waveform is very ringy because I did a lousy job of decoupling the power supply (stood a ceramic 0.1 across the IC without chopping its leads down). You can change the W/F just by bending this component about. It could be fixed but... time's up!

E2A, I semi-fixed it (relocated the bypass cap and poked the probe direct into the breadboard)

_q12x_ · May 18, 2022

very interesting update.
I managed to split 1/10 of my test PWM original fv. From its 850Hz down to 85Hz
Now Im playing with some capacitors values to bring it down to 1/100.
My target end result will be 1/1000.
And, I did managed to --average-- the 1/100 values. I say average because the fv counter is jumping a couple of Hz up and down. It should be 8.5Hz but is heavily fluctuating with diverse values between 10Hz and 6Hz. So I am theoretically at 8 but because is jumping all around these values, it was hard in the beginning to understand where I stand. But staying and watching these values for a while, a couple of minutes, I concluded it is jumping around these margins. That might be from the High resolution of the splitting, all the circuit(s) combined might present some tolerances, especially the capacitors and resistors and why not the chip(s).
At 1/10, it does not jump at all, it stays put at that fv. So.... I think im good at this point.
I might have to make a second circuit that will split another 1/10 from this one that is 1/100 and in the final output will get 1/1000. And I expect it will be extremely jumpy at that Very High resolution. If it is a way of "average" all these jumping, especially at 1/100 stage I am right now. That will give a good clear chance for the 1/1000 stage. Hmmm. But it is in plan. For now, I have to reach that 1/1000 target and Im GOOD, literally. Haha.

marconi · May 19, 2022

pc1966 said:
A crude simulation attempt, did not work at 20MHz with 2N2222 but OK with BC548, also used low-Q crystal model so faster to build up (along with 1mV kick at t=0)
View attachment 97652

Time-domain for test point in Tr1 collector:
View attachment 97653

I had another go this morning after thinking about the small signal model of this circuit and why the ratio of Rc to Re matters so much- see first attachment. I tried Rc = 1kR and Re = 4.7kR and even exchanged the BC549s for two new but in my construction it did not oscillate. Not enough feedback methinks so I swapped Rc for 100R and the symmetrischer oszillator found its 20MHz voice. We did it Sir and self starting to boot!

pc1966 · May 19, 2022

marconi said:
Not enough feedback methinks so I swapped Rc for 100R and the symmetrischer oszillator found its 20MHz voice. We did it Sir and self starting to boot!

Excellent!

While the E-E impedance should be roughly -2*Rc quite possibly the higher Rc values along with stray capacitance might cause too much phase shift. I seem to recall that 10-20MHz crystals are below 100R series resistance so indeed 100R values for Rc would be adequate, as you have so well demonstrated!

Make a very simple test for me

_q12x_

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pc1966

Lightning & Thunderstorms - United Kingdom, England, Scotland, Wales, Ireland

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