Oscilloscope capability is expressed in MHz (20MHz .. 100MHz, etc.), usb acquisition card working as oscilloscopes have their capability expressed in samples/s, as far as I understood.
Is there a direct relationship between samples/s and MHz?
If the usb card acquisition is let's say 100ks/s, does it mean 100KHz? Kind of low compare to simple/old oscilloscopes rated for 5-10MHz.
Not having an oscilloscope, I am interested in the two following items:
- EspoTek Labrador Board (EspoTek Labrador – Official EspoTek Online Store),
- iCP12B - usbStick (iCP12B (1mV+) - usbStick (Micro USB DAQ, PC Oscilloscope, Data Logger, Frequency Generator, PIC18F2553 IO Board)).
Any member tried them?
How do you think they compare versus simple low end oscilloscopes?
Is there a direct relationship between samples/s and MHz?
If the usb card acquisition is let's say 100ks/s, does it mean 100KHz? Kind of low compare to simple/old oscilloscopes rated for 5-10MHz.
Not having an oscilloscope, I am interested in the two following items:
- EspoTek Labrador Board (EspoTek Labrador – Official EspoTek Online Store),
- iCP12B - usbStick (iCP12B (1mV+) - usbStick (Micro USB DAQ, PC Oscilloscope, Data Logger, Frequency Generator, PIC18F2553 IO Board)).
Any member tried them?
How do you think they compare versus simple low end oscilloscopes?
A waveform is a continuous locus of points. This means in theory an infinite number of samples is required. In reality, this is not possible, so we have to be contented with less points to describe a waveform. The more complex a waveform is the more points are required. If the waveform is known less points are required and extrapolation can be used.
So, the answer is it depends on what signal you want to display.
So, the answer is it depends on what signal you want to display.
>Is there a direct relationship between samples/s and MHz?
Theoretically, you want at least 2 samples per Hz, but I prefer 10. 10 is an easy number; if the channel samples at 1MHz, it's good for capturing a useful waveform up to 100KHz. Should be plenty good for audio waveforms.
The scope as a unit - versus a card or stick - has the advantage that it's a monolithic device; it'll still be available when you upgrade laptop / operating system. How many USB devices can you count that are now garbage because the manufacturer decided - for whatever reason - not to support "windows 10" drivers?
Theoretically, you want at least 2 samples per Hz, but I prefer 10. 10 is an easy number; if the channel samples at 1MHz, it's good for capturing a useful waveform up to 100KHz. Should be plenty good for audio waveforms.
The scope as a unit - versus a card or stick - has the advantage that it's a monolithic device; it'll still be available when you upgrade laptop / operating system. How many USB devices can you count that are now garbage because the manufacturer decided - for whatever reason - not to support "windows 10" drivers?
Last edited:
Even for audio work, you need more than 100 kHz bandwidth, ideally at least. I've seen many amplifiers oscillate above 5 MHz, and that includes tube stages. Op-amps can do it too.
I recently had a MOSFET amplifier that went into a fairly violent 15 MHz oscillation. So a real 20 MHz oscilloscope is sort of a minimum. You can get away with a sound card, but an analog oscilloscope can be picked up pretty cheap these days and is definitely a big improvement.
I recently had a MOSFET amplifier that went into a fairly violent 15 MHz oscillation. So a real 20 MHz oscilloscope is sort of a minimum. You can get away with a sound card, but an analog oscilloscope can be picked up pretty cheap these days and is definitely a big improvement.
There are cheap PC scopes with 100MSPS and more. They are mostly 8bit resolution so not the best for low level probing. Soundcards may have very low bandwidth but they have 16bit or more resolution.
But detecting hf oscillations and other details are most important imo. Besides a pc scope has a more practical interface and handles higher voltages than a usb soundcard.
But detecting hf oscillations and other details are most important imo. Besides a pc scope has a more practical interface and handles higher voltages than a usb soundcard.
I have a 1GHz 'usb scope', and I think that a 1GHz 'real' scope will be at least as expensive, probably more.
If you are starting with scopes, you will need some time and activity to get up to speed and comfortably with such a piece of equipment; there's much more than just looking at a sinewave.
So in that case you are better off with a traditional scope because you don't need the added complexity of learning software while also learning to use a scope.
After you get some experience you can decide how to move forward, you will know what you really need.
Again, in that case you'd be better off with starting on a used 200 or 300MHz MHz Tek or Agilent as they are available for a few 100 dollars.
Ohh, and get a 4-channel instead of a 2-channel if you can. You always need more channels to look at different points in your circuits.
Jan
If you are starting with scopes, you will need some time and activity to get up to speed and comfortably with such a piece of equipment; there's much more than just looking at a sinewave.
So in that case you are better off with a traditional scope because you don't need the added complexity of learning software while also learning to use a scope.
After you get some experience you can decide how to move forward, you will know what you really need.
Again, in that case you'd be better off with starting on a used 200 or 300MHz MHz Tek or Agilent as they are available for a few 100 dollars.
Ohh, and get a 4-channel instead of a 2-channel if you can. You always need more channels to look at different points in your circuits.
Jan
Thanks for your comment Jan.
In point of fact I was using oscilloscopes for my work. Had an old one at home too but had to discard it after years of no-use while abroad. Using one is not a problem I think.
Was using acquisition cards/softwares too at work.
Now it's for private use. Saw several usb-based scopes on the net. Wondering where to spend the money, and why specifications are not expressed the same way (Hz v. samples/s).
4 channels instead of 2. Can become handy. 2 channels in the labrador board.
In point of fact I was using oscilloscopes for my work. Had an old one at home too but had to discard it after years of no-use while abroad. Using one is not a problem I think.
Was using acquisition cards/softwares too at work.
Now it's for private use. Saw several usb-based scopes on the net. Wondering where to spend the money, and why specifications are not expressed the same way (Hz v. samples/s).
4 channels instead of 2. Can become handy. 2 channels in the labrador board.
That ratio of at least 2 to 1 (sampling frequency at least twice the maximum signal frequency) is no coincidence. You will see that in every system that samples analog signals.
The reason is the Shannon-Nyquist sampling theorem. (Nyquist–Shannon sampling theorem - Wikipedia)
Accurately reconstructing an analog signal from the sampled data requires at least two data points per cycle of the signal.
As a consequence, the maximum bandwidth of a sampled signal is half the sampling rate.
The practical limit is lower, and it depends on how sharp the filters are that remove the out of bounds content. A better filter lets you get closer to the theoretical bandwidth.
Sampling rate tells you how fast the samples are taken.
Bandwidth includes the cutoff frequency of the analog circuitry and filters before the analog to digital conversion.
Any decent oscilloscope or USB data acquisition (DAQ) card will tell you both.
-------
Besides sampling rate and bandwidth, you need to keep an eye on the input voltage range.
Microphone signals can be down in the single digit millivolt peak to peak range, while speaker signals can be many volts to tens of volts peak to peak.
You need to make sure that your scope can cover the voltage levels that you will be working with.
My old analog oscilloscope has (by modern standards) a low bandwidth of only around 15MHz. On the other hand, it has a stupidly high range of voltage settings - I can measure stuff from less than 100 microvolts up to a couple of hundred volts with it.
The reason is the Shannon-Nyquist sampling theorem. (Nyquist–Shannon sampling theorem - Wikipedia)
Accurately reconstructing an analog signal from the sampled data requires at least two data points per cycle of the signal.
As a consequence, the maximum bandwidth of a sampled signal is half the sampling rate.
The practical limit is lower, and it depends on how sharp the filters are that remove the out of bounds content. A better filter lets you get closer to the theoretical bandwidth.
Sampling rate tells you how fast the samples are taken.
Bandwidth includes the cutoff frequency of the analog circuitry and filters before the analog to digital conversion.
Any decent oscilloscope or USB data acquisition (DAQ) card will tell you both.
-------
Besides sampling rate and bandwidth, you need to keep an eye on the input voltage range.
Microphone signals can be down in the single digit millivolt peak to peak range, while speaker signals can be many volts to tens of volts peak to peak.
You need to make sure that your scope can cover the voltage levels that you will be working with.
My old analog oscilloscope has (by modern standards) a low bandwidth of only around 15MHz. On the other hand, it has a stupidly high range of voltage settings - I can measure stuff from less than 100 microvolts up to a couple of hundred volts with it.
OK I misread, apologies.
I got several USB scopes from TiePie engineering in Holland. The nice thing about them is that they are 8 or 10bit at the widest bandwidth, but can run 14 or 16 bit with reduced bandwidth. And that is exactly what comes handy in audio work, higher bit depth and a bandwidth less than light.
As a matter of fact I am selling my HS3-25MHz with arbitrary waveform generator ;-) . € 350 + shipping in case you (or anybody else) is interested.
Jan
Last edited:
It depends on how optimistic the USB scope seller is.
Some say MHz = Meg samples/second.
Usually its less MHz than Meg samples/second.
How many dots(samples) on the screen do you need to represent a sine wave for example?
For a decent sine wave I would reckon about a hundred dots.
So that means a 100 meg samples/sec scope can manage 1MHz sine wave.
While I design and sell USB scopes I rarely use one unless I want digital storage. I much prefer my analogue scope for every day use.
It has been suggested you need two points for a sine wave. Ok you can extrapolate the sine wave but what if its a triangle wave or square wave ?
Nigel, I think it depends on the architecture. You need only two points to recreate a sine wave, assuming your anti-aliasing is up to snuff.
You really don't need to individual dots to show on a digital display, just paint the wave.
For several reasons you may want to go a hit further, like 3 or 4 points per period to ease on the low pass, but 100 points seems excessive.
Jan
You really don't need to individual dots to show on a digital display, just paint the wave.
For several reasons you may want to go a hit further, like 3 or 4 points per period to ease on the low pass, but 100 points seems excessive.
Jan
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.