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46

You should never float a scope with an isolation transformer! This is reckless and dangerous advice from your professor, and he/she needs a reality check. The accepted procedure for doing work that requires isolation is to ISOLATE THE UNIT UNDER TEST, NOT THE TEST EQUIPMENT. Why? It's much easier to remember that the unit under test is what's unsafe and ...


34

Here's how you read the oscilloscope waveform. I took the time to edit your waveform picture and annotate it to show which bit is which. The microcontroller sends 10 bits per character; START, which is always 0, 8 data bits and STOP which is always 1. The line also rests at 1, so the first START falling edge alerts the receiver that a bytes is coming. The ...


33

I'd firstly agree with other posters as to economics of scale. Consumer devices are produced in the millions whereas such a market does not exist for digital oscilloscopes. Secondly, oscilloscopes are precision devices. They need to undergo rigorous quality control to ensure they live up to expected standards. This further increases costs. As for bandwidth....


29

Oscilloscope probes aren't just pieces of wire with pointy end attached to them. Typical probe will in addition to the pointy stick and the alligator clip have the input attenuation circuitry and impedance matching circuitry inside. Basically the oscilloscope input front-end has its own internal capacitance and its own internal resistance. In order to ...


26

System bandwidth is a combination of probe bandwidth and oscilloscope input bandwidth. Each can be approximated by an RC lowpass circuit, which means delays add geometrically: t_system^2 = (t_probe^2 + t_scope^2) f_system = 1/sqrt((1/f_probe)^2 + (1/f_scope)^2) This means that a 10MHz 'scope with 60MHz probes can measure sinusoids of frequency 9.86MHz ...


26

Bulk transfers do not lose data, but they have no guaranteed minimum bandwidth. (On the other hand, they can reach higher speeds, because they are able to use all the bandwidth not actually used by any other transfers.) What happens when your oscilloscope's data transfers are delayed (either because of errors, or because of other devices), and new data is ...


25

The DSO Nano is a poor choice for a hobbyist's oscilloscope. Capabilities It's really only good for audio bandwidth signals - anything above 100kHz is going to be visible, but unmeasurable. By most standards you want the sampling rate to be 10x the bandwidth of the signal in order to get close to measuring significant parameters of the signal (peaks, rise ...


25

Yes, that's normal. Due to its high impedance the probe acts as an antenna for the 50Hz field from the mains which fills the space surrounding the wiring (i.e. any room in your house). You'll notice that touching the probe will even show a stronger signal, indicating that your body is even a better antenna.


25

You should check the datasheet to be sure, but the usual cause would be that ultracaps are often quite limited in terms of current they can provide. You're trying to draw about 100 mA, while most ultracaps are rated at 1-10 mA discharge current. BTW, I suggest you stop your experiments if you need that cap later on. You can easily damage an ultracap by an ...


24

The alligator clip on the scope probe: (image source) is connected, through the power cord, to Earth. If you clip it to something that isn't at Earth potential, you get a large current, and things go boom. That said, an isolation transformer on the scope isn't the way to go. There's a reason the engineers built the scope like this, and it has to do with ...


23

Economy of scale -- the other items you mentioned are consumer devices, manufactured in the millions. Oscilloscopes will be manufactured in the thousands (or less), which makes a huge difference in amortized R&D, BOM (bill of material) and assembly costs.


22

Oscilloscopes usually require significant power and are physically big. Having a chassis that size, which would include exposed ground on the BNC connectors and the probe ground clips, floating would be dangerous. If you have to look at waveforms in wall-powered equipment, it is generally much better to put the isolation transformer on that equipment ...


22

This comes down to a question of bandwidth and latency. For a simple system let's assume one probe with 100 MHz bandwidth with 1GS/s sampling rate and an 10-bit A/D converter (I've had bad experiences with 8-bit scopes). I want a real-time display on the PC with a minimum sampling window of let's say 10ns - 1 cycle of a 100MHz sine wave and a maximum ...


21

Sounds like the scope is expecting a 10x probe (which attenuates the signal 10x), but you are using a 1x probe instead, therefore the scope is multiplying the signal by 10 when it shouldn't be. Check your settings.


20

The first thing I would do is read some literature on how scopes work. Tektronix has a good white paper called XYZs of Oscilloscopes. Next, you should hook up a function generator and figure out how the different display controls work. This includes the Y scale [Volts] and the X scale [Time]. Once you feel comfortable with those get comfortable using ...


20

At it's heart, a (digital) oscilloscope is just an ADC, along with some memory to hold the samples. The samples are then read out of the memory and displayed. The practical implementation issues make commercial oscilloscopes complicated. The input signal needs to be scaled appropriately for the range of the ADC, which means that you need to have attenuators ...


20

USB 3.0 runs the extra lanes at 5Gbps, which equates to a clock of 2.5GHz. So you will probably need at least 3GHz bandwidth, at an absolute minimum. Quite pricey! To see anything clearly, you'll want even more bandwidth as the signals have multiple harmonics - you would need at least the 3rd at 7.5GHz and preferably the 5th harmonic at 12.5GHz to see ...


19

Nothing. That is, you'll just see a flat line, as if there's no signal. It's too high frequency to see. The input stage on a 50 MHz scope is not configured to pass a 2.4 GHz signal. It'll be filtered out, and you'll be left looking at the (probably nonexistent) low-frequency components of the signal.


18

You don't mention exactly what work you do, but a good digital storage oscilloscope (DSO) will last you a while (and I guarantee it won't go out of date for a while). Sure, you can grab a secondhand Tektronix analog oscilloscope, but my storage scope has saved my frustration bacon more than once. I have a Rigol DS1052E (a good review from a proper ...


18

Lower production volumes are a major cause and secondly, you're buying test equipment which is something special. If you only look at the teardown of a cheap DSO like a Rigol DS1052 you will see what's required just to make a low-entry scope. They have 5 dual ADC's (overclocked, so that already reduces pricing!). If those ADC's were $4 each (a random guess, ...


18

It's a "Probe tip ground clip" (or something very similar like the examples below) An example of it being named as such is here. It's called "Probe tip ground" here. It is also called a "Probe tip spring adapter" here. Whatever it's exact name, I think the main thing is to have "tip" in there, as it differentiates from the standard ground clip by implying ...


18

Don't ground the data lines. They are above ground. Beyond Logic says USB uses a differential transmission pair for data. This is encoded using NRZI and is bit stuffed to ensure adequate transitions in the data stream. On low and full speed devices, a differential ‘1’ is transmitted by pulling D+ over 2.8V with a 15K ohm resistor pulled to ground ...


17

The ground clip on your o-scope is actually tied to ground. it is a hard short and rather low resistance. This means that you are shorting the 3.3 rail to ground with your ground probe. To fix this there are two options, Put the resistor in the return path so that one side of it is ground. That way the ground probe does not hurt it. Use two probes, one ...


16

Use a transformer (12V, say), it will be much safer even if your scope will handle the mains voltage. That particular scope will probably be damaged, DO NOT connect it to the mains! 230 V is the rms voltage, the peak voltage is 230 * 1.412 V.


16

WARNING: Means of being less likely to die or to kill others is discussed below. Reading may be considered useful.. Consider this "informed opinion" rather than holy writ. In an oscilloscope you want the best result you can get for the money and it's far easier to build a single ended amplifier rather than a differential one when you want ruler flat gain ...


15

There are a few reasons for this: Nyquist's theorem applies to reconstruction of sinusoidal signals of infinite duration from jitter-free, perfectly accurate samples. Real measurement device clocks have jitter and fixed frequencies, real samples have measurement error and real signals are not infinite sinusoids. Jitter is the difference between a sample'...


15

I'm not sure what the distinction is between the two choices in your question, but the real answer is that the gain of the amplifier(s) inside the scope is "flat" up to that frequency. In other words, the voltage measurements you make on the screen will be "accurate" up to that frequency. Above that frequency, the values will appear smaller than they ...


15

If it's a good scope, you'll see nothing at all, just a flat line representing DC.. Ironically if it's an inferior scope with incompetently designed input amplifiers and the signal strength is high enough, you may see a step in the flat line when the poorly filtered RF carrier is demodulated by nonlinearities in the amplifier, but that will only tell you ...


15

Put the ground clips of two scope probes on the ground of the circuit (the one denoted with ground symbol). Then put Channel A on point A, channel B on point B, and then use the Math function of the scope to display the difference between two signals.


15

Please see this very useful explanation why USB D- is not a GND. If you want to probe USB data pairs; you need to connect your scope between GND and USB D- and/or D+. Also remember that in most PCs the "GND" is earthed; and so is your scope GND lead. This is likely the behaviour of shutting down because you are effectively connecting USB D- to GND (via ...



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