Question for the Oscilloscope Experts

rsfoto · Dec 17, 2015

audioguru said:
I think the 10uF output capacitor will take too long a time to charge. If the 10k output resistor is changed to 1M then the capacitor value can be reduced so that it charges much quicker.

I would say do not worry about those values as those 2 components will only be used if I want to use a DC flattened voltage as depicted in cowboybobs simulation.

cowboybob · Dec 17, 2015

That's true.

I'd be curious to see a 'scope display of the current circuit's output with the piezo input (may have to up the 1st OPA's gain).

rsfoto · Dec 17, 2015

cowboybob said:
That's true.

I'd be curious to see a 'scope display of the current circuit's output with the piezo input (may have to up the 1st OPA's gain).

How do I measure that with an Oscilloscope ?

cowboybob · Dec 18, 2015

rsfoto said:
How do I measure that with an Oscilloscope ?

Your 'scope's "Vert" (vertical) input(s) should have a switch with the options AC, Gnd and DC. Select the DC position plus a slow Horizontal (time base) of, say, 250 to 500mS and you should see a trace following the variable* DC signal coming from your signal conditioning circuit. Play with the settings (Horizontal and Vertical) to get a trace that makes sense.

By way of explanation, when in the AC position, there is a decoupling capacitor in the circuit to eliminate the DC component of the test signal. The gnd position grounds out the input to the 'scope's vertical circuitry (but NOT the signal you are feeding it). The DC position lacks the decoupling cap, so all DC signal biases are passed to the vertical curcuitry (as well as AC elements - makes for a messy trace).

*Use the "drumming fingers" excitation - the toothbrush would be a too consistent signal for this exercise.

KeepItSimpleStupid · Dec 18, 2015

CBB:

I wasn't sure what you meant either. I thought you meant to basically look at the RAW output of the first stage with likely more gain. i.e. with the cap shorted.
So, you replied with "how to use an oscilloscope. Confused.

cowboybob · Dec 18, 2015

Hey, KISS!

I meant for rsfoto to look at the full-wave rectified (therefore sort of compiled) piezo signal with the 'scope. I wanted him to be able to see the varying DC so as to demonstrate the difference in an AC vs. DC signals.

Since we don't know what he intends to do with the information he's generating, I thought it would be helpful for us all to have an idea of the quality of that data.

Admittedly, a little 'scope training was also on my mind...

rsfoto · Dec 18, 2015

cowboybob said:
That's true.

I'd be curious to see a 'scope display of the current circuit's output with the piezo input (may have to up the 1st OPA's gain).

Hi cbb,

You talk about Current at the first stage and I ask " how to measure that " because I know that measuring current with an Oscilloscope is not an easy task

By the way answering your question about what I want to do with the signal look in this same topic at message # 29, message # 90, message # 96, message # 101

rsfoto · Dec 18, 2015

cowboybob said:
Your 'scope's "Vert" (vertical) input(s) should have a switch with the options AC, Gnd and DC. Select the DC position plus a slow Horizontal (time base) of, say, 250 to 500mS and you should see a trace following the variable* DC signal coming from your signal conditioning circuit. Play with the settings (Horizontal and Vertical) to get a trace that makes sense.

By way of explanation, when in the AC position, there is a decoupling capacitor in the circuit to eliminate the DC component of the test signal. The gnd position grounds out the input to the 'scope's vertical circuitry (but NOT the signal you are feeding it). The DC position lacks the decoupling cap, so all DC signal biases are passed to the vertical curcuitry (as well as AC elements - makes for a messy trace).

*Use the "drumming fingers" excitation - the toothbrush would be a too consistent signal for this exercise.

Hi cbb,

My Oscilloscope cost me US $ 99.00 so nothing sophisticated and no, it has no adjustment possibility for AC and Ground.

I read about how to measure current with an Oscilloscope but I really doubt that by using a low resistor value this one could be able to measure the voltage drop and from there calculate the delivered current of the Piezo sensor ...

I might try it because as we are not dealing with huge Ampere loads I guess nothing will happen to my Oscilloscope and if I fry it then I ahce the excuse to buy a better one in the region of perhaps US $ 200.00 to 500.00

I like the ones which I can connect to a PC because of portability. I am thinking of the PICO brand for example

http://www.picotech.com/products/oscilloscope

**broken link removed**

etc.

KeepItSimpleStupid · Dec 18, 2015

cowboybob said:
That's true.

I'd be curious to see a 'scope display of the current circuit's output with the piezo input (may have to up the 1st OPA's gain).

Post #242. No mention of "conventional current" at all. "current" in this case means the last design iteration.

I told ya this thread is getting confusing. Too much spiked Egg Nog?

rsfoto · Dec 18, 2015

KeepItSimpleStupid said:
Post #242. No mention of "conventional current" at all. "current" in this case means the last design iteration.

I told ya this thread is getting confusing. Too much spiked Egg Nog?

ha ha ha not yet. Starting next Monday, but I do not like Egg Nog, I like your Maker's Mark

If you would have put actual circuit, I would have understood but as we are in an Electronic forum Current for me is Current eg. the electrones wandering from one side to the other due to a potential difference = voltage

rsfoto · Dec 18, 2015

KeepItSimpleStupid said:
Post #242. No mention of "conventional current" at all. "current" in this case means the last design iteration.

I told ya this thread is getting confusing. Too much spiked Egg Nog?

Hi cbb and kiss,

Your wishes are orders

Current circuit ... with a gain of 12

Here a video measuring on PIN 3 ( GREEN curve ) on Unit-1A and Yellow curve is on Output Unit-2B **broken link removed** (drumming fingers) You can see the voltage values for CH1 and CH2 on the lower part of the video

The next video is when a small screwdriver falls from about a height of 10cm on my table at a distance of 1 meter **broken link removed**

What do you think ?

rsfoto · Dec 18, 2015

Another one

Video as a message before but this time using a HiTec Vibration Generator

Video here **broken link removed**

cowboybob · Dec 18, 2015

rsfoto said:
That is exactly what I want to do. Measure the vibration of the pier on which the telescope mount is mounted in order to know when it is vibrating too much. More or less a simple seismograph

and
The others you noted pretty much reiterate the above quote.

And sorry about the "current" issue; at the time I was afraid it could be misinterpreted but I didn't go make and make it clear. My bad...
Anyway, it looks like all you need is some sort of "vibration intensity" display and, frankly, I think the most dramatic AND dynamic would be your PC oscilloscope! High tech, Real time and when you develop a vibration intensity scale based on voltage levels you'll have a very effective demonstration package.

Does you PC 'scope have memory? A pause Function? The .WMV file output is a very effective demo and could be used as a comparison SiesmoVID (just made that up ) when testing someone else's site.

You could "clean up" or smooth the output a bit with the cap/resistor circuit at the final output - your call.

As for the AC/Gnd/DC issue, it appears that you do, indeed, have those options on both vertical channels:
just not real switches. At my age I keep forgetting the virtual world stuff out there.

Your "HiTec Vibration Generator" is a gem of what we Hams call "Home Brew" gear... .

rsfoto · Dec 18, 2015

cowboybob said:
The others you noted pretty much reiterate the above quote.

Sorry

cowboybob said:
As for the AC/Gnd/DC issue, it appears that you do, indeed, have those options on both vertical channels:

No possibility to switch anything. Have gone through all menus at the top and nothing. Maybe I overlooked something and will do through it again

cowboybob said:
Does you PC 'scope have memory? A pause Function?

YES it does

cowboybob said:
You could "clean up" or smooth the output a bit with the cap/resistor circuit at the final output - your call.

Will play around with that. Thanks

cowboybob said:
The .WMV file output is a very effective demo and could be used as a comparison SeismoVID (just made that up ) when testing someone else's site

That is a very good idea

cowboybob said:
And sorry about the "current" issue; at the time I was afraid it could be misinterpreted but I didn't go make and make it clear. My bad...

Do not worry, can happen especially if the other person, me, English is not my mother language or somehow I did not understand it in that context

cowboybob said:
Your "HiTec Vibration Generator" is a gem of what we Hams call "Home Brew" gear... .

Thanks. That is a motor from a printer I ripped apart a few years ago and as I have some LiPo here I can take out 3.7V, 7.4V and 11.1V

CBB, are you a radio amateur ? ¿ HAM ?

cowboybob · Dec 18, 2015

rsfoto said:
CBB, are you a radio amateur ? ¿ HAM ?

Yes, I am - K4NFF (got my first ticket, KN4NFF, in 1959). Only tube type gear (HeathKit DX-60 & SB102) and not on the air much anymore.

BTW, I wasn't being critical in the first quote of yours above, just didn't see the need to quote all of the posts you noted. No need to apologize, I assure you.

rsfoto · Dec 18, 2015

cowboybob said:
You could "clean up" or smooth the output a bit with the cap/resistor circuit at the final output - your call.

Something like this ?

cowboybob · Dec 18, 2015

rsfoto said:
Something like this ?

View attachment 96211

Yes. It might not be necessary to make any circuit alterations. Just play with the scope settings to get the most useful and demonstrative examples of the vibrations being monitored.

rsfoto · Dec 18, 2015

cowboybob said:
Yes. It might not be necessary to make any circuit alterations.

I just added a 0.010μF cap and a 100K resistor and that is the result.

cowboybob said:
Just play with the scope settings to get the most useful and demonstrative examples of the vibrations being monitored.

Yes I have been doing that and at the moment I have some tiny helpers at home. My grandchildren 4 and 6 years old. I have put them to march here and so I see the vibrations of the floor

audioguru · Dec 18, 2015

1) The datasheet for your vibration sensor says, "Operation up to 40Hz" because it has a strong resonance at 75Hz. Your circuit has no lowpass filter at 40Hz.
2) You have C2 as a low value 220nF capacitor and R5 as a low value 10k resistor which cut frequencies below 73Hz but vibrations are much lower. If you use 220nF then the R4 should be 470k then for the same gain as now R5 should also be 470k and the pot should be 4.7M. Maybe you should use a 1uF film capacitor and these higher resistor values for even lower frequencies.
3) Your unshielded wiring or many wires on a solderless breadboard are picking up a lot of 60Hz mains electricity hum.
4) The first opamp has a gain of only 2 so it is it needed. Increase the gain of the second opamp instead with R1 at its input.
5) The outputs of opamps 2A and 2B alternate slamming as low as they can go because you do not have a correct fullwave rectifier circuit.

rsfoto · Dec 18, 2015

audioguru said:
1) The datasheet for your vibration sensor says, "Operation up to 40Hz" because it has a strong resonance at 75Hz. Your circuit has no lowpass filter at 40Hz.
2) You have C2 as a low value 220nF capacitor and R5 as a low value 10k resistor which cut frequencies below 73Hz but vibrations are much lower. If you use 220nF then the R4 should be 470k then for the same gain as now R5 should also be 470k and the pot should be 4.7M. Maybe you should use a 1uF film capacitor and these higher resistor values for even lower frequencies.
3) Your unshielded wiring or many wires on a solderless breadboard are picking up a lot of 60Hz mains electricity hum.
4) The first opamp has a gain of only 2 so it is it needed. Increase the gain of the second opamp instead with R1 at its input.
5) The outputs of opamps 2A and 2B alternate slamming as low as they can go because you do not have a correct fullwave rectifier circuit.

Hi ag,

Starting next monday I will be in vacation for 2 weeks ans then take the time to set up everything soldered on a board an test it in the Observatory. I already have a copper mesh with which I will build a Faraday cage and so I will see what comes out.

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