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.

marconi · May 19, 2022

q12x. : My next step is to take the small amplitude 20MHz sine wave and turn it into 20MHz pulse stream of TTL logic 0 and 1s to feed into the divider circuit.

_q12x_ · May 19, 2022

Congratulation mister @marconi I am really happy you made it !
But I am not sure I understand completely your values.
So I grabbed all the information you provided so far:

marconi said:
Rc for 100R and the symmetrischer oszillator found its 20MHz voice.

marconi said:
did not work at 20MHz with 2N2222 but OK with BC548

marconi said:
I tried Rc = 1kR and Re = 4.7kR

and I redraw the circuit with the new values:
- Are these the values you used?

marconi · May 19, 2022

_q12x_ said:
Congratulation mister @marconi I am really happy you made it !
But I am not sure I understand completely your values.
So I grabbed all the information you provided so far:

and I redraw the circuit with the new values:
- Are these the values you used?
View attachment 97682

Yes. VB is 5 Volts not 1.35V. The npn transistors are BC548B types. the letter A, B or C after BC548 indicates the so-called direct current gain of the transistor - the hFE - and relates the emitter-collector current flow to the base-emitter current flow eg: Ice/Ibe. Which BC548s do you have? Cs have higher gain than Bs than As so I used the mid-range gain type.

See top of page 2 of:

BC548B datasheet - https://datasheetspdf.com/pdf-file/1292183/Kingtronics/BC548B/1

marconi · May 19, 2022

Which operational amplifiers do you have please and I will use the same ones to amplify the small amplitude 20MHz sine wave.

_q12x_ · May 19, 2022

Mine are BC548 B - coincidence! like yours.
I have uA741(not that used anymore) and LM358(most used)
Updated circuit after your last specifications:
Ive added + and 5V and gnd symbol. Also B after tr name.

_q12x_ · May 19, 2022

My last night progress:

The fv Counter is reading the output of the frequency divider and is reading 1/100 = (around) 8.5Hz
(The osciloscope reading is intermittent for this 8.5Hz output, not the same every time)
The osciloscope shown here is reading the output of the PWM at 850Hz

And now, Im building the board of the frequency divider:

_q12x_ · May 19, 2022

Mister @marconi and @pc1966 , in my post #73 I had a problem:
"..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 jumpings, 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.. "
- Can you give me an answer to this problem?
I have an idea but I think is a bit too complicated.... and is incomplete as well.
I want to see what are your thoughts.

marconi · May 19, 2022

Impressive progress and great dedication.

_q12x_ · May 19, 2022

deleted post ______

_q12x_ · May 19, 2022

marconi said:
Impressive progress and great dedication.

True, true,
The same to you
haha

marconi · May 19, 2022

To use a 555 as a frequency divider of a known and constant frequency pulse train you have to make sure that the 555 is ready to be triggered again after n input pulses where n is the division factor.

This means that one has to ensure the 555 output (shown in green) has changed to zero after a further n input pulses (shown in yellow) since it was last triggered so the 555 is ready to be triggered again by first pulse of the next group of n pulses.

The way the 555 retriggerable monostable circuit operates to divide by n means that the time constant/period of the monostable 555 - x - must satisfy this equation:

(n x T) - t < x < (n x T)

What this says is the 555 output must transition to zero after the trailing edge of the nth pulse and before the leading edge of the (n+1)th pulse - that is in the gap between them when the input is zero.

Attached is an example for a divide by 3 scheme which shows the meaning of n, T, t and x.

It is probable better then for your PWM input to keep t short with respect to T so that there is a relatively big time gap between input pulses so that variations in the 555 timer function which creates the interval x will generally fall clearly after n pulses and nicely before the (n+1)th.

Or something close to this explanation - I am bit rushed.

_q12x_ · May 19, 2022

So... no answer. Ok.
And I finished the board. it took me exactly 3h to make it (continuous work, no brakes).

Is the small right (card)board

Not bad !
Now I can make another division, 1/10 to get a total of 1/1000.
It would be nice if you could look over the "average" problem, but... you are busy as well I guess.
I will probably not implement it, but it will had give me a very clean result in the final stage....
As I said, we'll see after I finish the whole 1/1000 process then.

marconi · May 19, 2022

So... no answer. Maybe not the complete answer you were expecting but something for you to consider. The explanation suggests pointers on what you might do to 'tweak' your design so that division by n actually occurs in the real circumstances of the circuit when the input period T and pulse duration t are varying randomly and the monostable duration x is subject to random lengthening and shortening in time. In plain English/Romanian make sure the on to off ratio of the input pulse stream is less than 5%(say) and n is high.

_q12x_ · May 19, 2022

I still don get it.... make me a clear circuit... or a continuation of the one that I have already, Like another module to add after the last 1/100 output (that Im actually measure with the fv counter).
Draw on paper and make a picture and post it.

marconi · May 19, 2022

I and you do not know whether the variation in division result is due to variation of the input from your PWM circuit or in your 555 divider circuit or both. All I can say is the variation becomes less significant if the mark-space ratio of the input is low and n is higher. That is how the mathematics works.

To do the averaging one would need to store values over an interval which can be done but at the moment I do not think you have the ics to do that. When my parcel arrives maybe but then you can do the division in a much more practical way to not bother.